Lead

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Lead,  82Pb
Lead electrolytic and 1cm3 cube.jpg
Lead
Pronunciation /ˈlɛd/ (LED)
Appearancemetallic gray
Standard atomic weight Ar, std(Pb)207.2(1) [1]
Lead in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Sn

Pb

Fl
thalliumleadbismuth
Atomic number (Z)82
Group group 14 (carbon group)
Period period 6
Block p-block
Element category   Post-transition metal
Electron configuration [ Xe ] 4f14 5d10 6s2 6p2
Electrons per shell
2, 8, 18, 32, 18, 4
Physical properties
Phase at  STP solid
Melting point 600.61  K (327.46 °C,621.43 °F)
Boiling point 2022 K(1749 °C,3180 °F)
Density (near r.t.)11.34 g/cm3
when liquid (at m.p.)10.66 g/cm3
Heat of fusion 4.77  kJ/mol
Heat of vaporization 179.5 kJ/mol
Molar heat capacity 26.650 J/(mol·K)
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)97810881229141216602027
Atomic properties
Oxidation states −4, −2, −1, +1, +2, +3, +4 (an  amphoteric oxide)
Electronegativity Pauling scale: 1.87 (+2)
Ionization energies
  • 1st: 715.6 kJ/mol
  • 2nd: 1450.5 kJ/mol
  • 3rd: 3081.5 kJ/mol
Atomic radius empirical:175  pm
Covalent radius 146±5 pm
Van der Waals radius 202 pm
Color lines in a spectral range Lead spectrum visible.png
Color lines in a spectral range
Spectral lines of lead
Other properties
Natural occurrence primordial
Crystal structure face-centered cubic (fcc)
Cubic-face-centered.svg
Speed of sound thin rod1190 m/s(at r.t.)(annealed)
Thermal expansion 28.9 µm/(m·K)(at 25 °C)
Thermal conductivity 35.3 W/(m·K)
Electrical resistivity 208 nΩ·m(at 20 °C)
Magnetic ordering diamagnetic
Magnetic susceptibility 23.0×10−6 cm3/mol(at 298 K) [2]
Young's modulus 16 GPa
Shear modulus 5.6 GPa
Bulk modulus 46 GPa
Poisson ratio 0.44
Mohs hardness 1.5
Brinell hardness 38–50 MPa
CAS Number 7439-92-1
History
Discovery in the Middle East (7000 BCE)
Main isotopes of lead
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
204Pb1.4% stable
206Pb24.1%stable
207Pb22.1%stable
208Pb52.4%stable
Isotopic abundances vary greatly by sample
| references

Lead ( /ˈlɛd/ ) is a chemical element with the symbol Pb (from the Latin plumbum) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, lead is silvery with a hint of blue; it tarnishes to a dull gray color when exposed to air. Lead has the highest atomic number of any stable element and three of its isotopes are endpoints of major nuclear decay chains of heavier elements.

Chemical element a species of atoms having the same number of protons in the atomic nucleus

A chemical element is a species of atom having the same number of protons in their atomic nuclei. For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have 8 protons.

Symbol (chemistry) an arbitrary or conventional sign used in chemical science to represent a chemical element

In chemistry, a symbol is an abbreviation for a chemical element. Symbols for chemical elements normally consist of one or two letters from the Latin alphabet and are written with the first letter capitalised.

Latin Indo-European language of the Italic family

Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets and ultimately from the Phoenician alphabet.

Contents

Lead is a relatively unreactive post-transition metal. Its weak metallic character is illustrated by its amphoteric nature; lead and lead oxides react with acids and bases, and it tends to form covalent bonds. Compounds of lead are usually found in the +2 oxidation state rather than the +4 state common with lighter members of the carbon group. Exceptions are mostly limited to organolead compounds. Like the lighter members of the group, lead tends to bond with itself; it can form chains and polyhedral structures.

Post-transition metal Category of metallic elements

Post-transition metals are a set of metallic elements in the periodic table located between the transition metals to their left, and the metalloids to their right. Depending on where these adjacent groups are judged to begin and end, there are at least five competing proposals for which elements to include: the three most common contain six, ten and thirteen elements, respectively. All proposals include gallium, indium, tin, thallium, lead, and bismuth.

Lead oxides are a group of inorganic compounds with formulas including lead (Pb) and oxygen (O).

Acid type of chemical substance that reacts with a base

An acid is a molecule or ion capable of donating a proton (hydrogen ion H+), or, alternatively, capable of forming a covalent bond with an electron pair (a Lewis acid).

Lead is easily extracted from its ores; prehistoric people in Western Asia knew of it. Galena, a principal ore of lead, often bears silver, interest in which helped initiate widespread extraction and use of lead in ancient Rome. Lead production declined after the fall of Rome and did not reach comparable levels until the Industrial Revolution. In 2014, the annual global production of lead was about ten million tonnes, over half of which was from recycling. Lead's high density, low melting point, ductility and relative inertness to oxidation make it useful. These properties, combined with its relative abundance and low cost, resulted in its extensive use in construction, plumbing, batteries, bullets and shot, weights, solders, pewters, fusible alloys, white paints, leaded gasoline, and radiation shielding.

Ore rock with valuable metals, minerals and elements

An ore is a natural occurrence of rock or sediment that contains sufficient minerals with economically important elements, typically metals, that can be economically extracted from the deposit. The ores are extracted at a profit from the earth through mining; they are then refined to extract the valuable element or elements.

The metals of antiquity are the seven metals which humans had identified and found use for in prehistoric times: gold, silver, copper, tin, lead, iron, and mercury. These seven are the metals from which the modern world was forged; until the discovery of arsenic in the 13th century, these were the only known elemental metals, compared to the 86 known today.

Galena Rocksalt group, sulfide mineral

Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver.

In the late 19th century, lead's toxicity was recognized, and its use has since been phased out of many applications. However, many countries still allow the sale of products that expose humans to lead, including some types of paints and bullets. Lead is a neurotoxin that accumulates in soft tissues and bones; it damages the nervous system and interferes with the function of biological enzymes, causing neurological disorders, such as brain damage and behavioral problems.

Lead poisoning Poisoning by lead in the body, especially affects the brain

Lead poisoning is a type of metal poisoning caused by lead in the body. The brain is the most sensitive. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, inability to have children, and tingling in the hands and feet. It causes almost 10% of intellectual disability of otherwise unknown cause and can result in behavioral problems. Some of the effects are permanent. In severe cases anemia, seizures, coma, or death may occur.

Neurotoxin substance poisonous or destructive to nerve tissue

Neurotoxins are toxins that are destructive to nerve tissue. Neurotoxins are an extensive class of exogenous chemical neurological insults that can adversely affect function in both developing and mature nervous tissue. The term can also be used to classify endogenous compounds, which, when abnormally contacted, can prove neurologically toxic. Though neurotoxins are often neurologically destructive, their ability to specifically target neural components is important in the study of nervous systems. Common examples of neurotoxins include lead, ethanol, glutamate, nitric oxide, botulinum toxin, tetanus toxin, and tetrodotoxin. Some substances such as nitric oxide and glutamate are in fact essential for proper function of the body and only exert neurotoxic effects at excessive concentrations.

Nervous system the entire nerve apparatus of the body

The nervous system is a highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes that impact the body, then works in tandem with the endocrine system to respond to such events. Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago. In vertebrates it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers or axons, that connect the CNS to every other part of the body. Nerves that transmit signals from the brain are called motor or efferent nerves, while those nerves that transmit information from the body to the CNS are called sensory or afferent. Spinal nerves serve both functions and are called mixed nerves. The PNS is divided into three separate subsystems, the somatic, autonomic, and enteric nervous systems. Somatic nerves mediate voluntary movement. The autonomic nervous system is further subdivided into the sympathetic and the parasympathetic nervous systems. The sympathetic nervous system is activated in cases of emergencies to mobilize energy, while the parasympathetic nervous system is activated when organisms are in a relaxed state. The enteric nervous system functions to control the gastrointestinal system. Both autonomic and enteric nervous systems function involuntarily. Nerves that exit from the cranium are called cranial nerves while those exiting from the spinal cord are called spinal nerves.

Physical properties

Atomic

A lead atom has 82 electrons, arranged in an electron configuration of [ Xe ]4f145d106s26p2. The sum of lead's first and second ionization energies—the total energy required to remove the two 6p electrons—is close to that of tin, lead's upper neighbor in the carbon group. This is unusual; ionization energies generally fall going down a group, as an element's outer electrons become more distant from the nucleus, and more shielded by smaller orbitals. The similarity of ionization energies is caused by the lanthanide contraction—the decrease in element radii from lanthanum (atomic number 57) to lutetium (71), and the relatively small radii of the elements from hafnium (72) onwards. This is due to poor shielding of the nucleus by the lanthanide 4f electrons. The sum of the first four ionization energies of lead exceeds that of tin, [3] contrary to what periodic trends would predict. Relativistic effects, which become significant in heavier atoms, contribute to this behavior. [lower-alpha 1] One such effect is the inert pair effect: the 6s electrons of lead become reluctant to participate in bonding, making the distance between nearest atoms in crystalline lead unusually long. [5]

Atom smallest unit of a chemical element

An atom is the smallest constituent unit of ordinary matter that constitutes a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small; typical sizes are around 100 picometers. They are so small that accurately predicting their behavior using classical physics – as if they were billiard balls, for example – is not possible. This is due to quantum effects. Current atomic models now use quantum principles to better explain and predict this behavior.

Electron subatomic particle with negative electric charge

The electron is a subatomic particle, symbol
e
or
β
, whose electric charge is negative one elementary charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, ħ. Being fermions, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy.

Electron configuration property of an atom

In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals. For example, the electron configuration of the neon atom is 1s2 2s2 2p6, using the notation explained below.

Lead's lighter carbon group congeners form stable or metastable allotropes with the tetrahedrally coordinated and covalently bonded diamond cubic structure. The energy levels of their outer s- and p-orbitals are close enough to allow mixing into four hybrid sp3 orbitals. In lead, the inert pair effect increases the separation between its s- and p-orbitals, and the gap cannot be overcome by the energy that would be released by extra bonds following hybridization. [6] Rather than having a diamond cubic structure, lead forms metallic bonds in which only the p-electrons are delocalized and shared between the Pb2+ ions. Lead consequently has a face-centered cubic structure [7] like the similarly sized [8] divalent metals calcium and strontium. [9] [lower-alpha 2] [lower-alpha 3] [lower-alpha 4]

Congener (chemistry) related chemicals

In chemistry, congeners are related chemical substances "related to each other by origin, structure, or function".

Covalent bond chemical bond that involves the sharing of electron pairs between atoms

A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding. For many molecules, the sharing of electrons allows each atom to attain the equivalent of a full outer shell, corresponding to a stable electronic configuration. In organic chemistry covalent bonds are much more common than ionic bonds.

Diamond cubic three-dimensional repeating pattern formed by the atoms of a diamond crystal

The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. While the first known example was diamond, other elements in group 14 also adopt this structure, including α-tin, the semiconductors silicon and germanium, and silicon/germanium alloys in any proportion.

Bulk

Pure lead has a bright, silvery appearance with a hint of blue. [14] It tarnishes on contact with moist air and takes on a dull appearance, the hue of which depends on the prevailing conditions. Characteristic properties of lead include high density, malleability, ductility, and high resistance to corrosion due to passivation. [15]

A sample of lead solidified from the molten state Lead-2.jpg
A sample of lead solidified from the molten state

Lead's close-packed face-centered cubic structure and high atomic weight result in a density [16] of 11.34 g/cm3, which is greater than that of common metals such as iron (7.87 g/cm3), copper (8.93 g/cm3), and zinc (7.14 g/cm3). [17] This density is the origin of the idiom to go over like a lead balloon. [18] [19] [lower-alpha 5] Some rarer metals are denser: tungsten and gold are both at 19.3 g/cm3, and osmium—the densest metal known—has a density of 22.59 g/cm3, almost twice that of lead. [20]

Lead is a very soft metal with a Mohs hardness of 1.5; it can be scratched with a fingernail. [21] It is quite malleable and somewhat ductile. [22] [lower-alpha 6] The bulk modulus of lead—a measure of its ease of compressibility—is 45.8  GPa. In comparison, that of aluminium is 75.2 GPa; copper 137.8 GPa; and mild steel 160–169 GPa. [23] Lead's tensile strength, at 12–17 MPa, is low (that of aluminium is 6 times higher, copper 10 times, and mild steel 15 times higher); it can be strengthened by adding small amounts of copper or antimony. [24]

The melting point of lead—at 327.5 °C (621.5 °F) [25] —is very low compared to most metals. [16] [lower-alpha 7] Its boiling point of 1749 °C (3180 °F) [25] is the lowest among the carbon group elements. The electrical resistivity of lead at 20 °C is 192 nanoohm-meters, almost an order of magnitude higher than those of other industrial metals (copper at 15.43 nΩ·m; gold 20.51 nΩ·m; and aluminium at 24.15 nΩ·m). [27] Lead is a superconductor at temperatures lower than 7.19  K; [28] this is the highest critical temperature of all type-I superconductors and the third highest of the elemental superconductors. [29]

Main isotopes of lead (82Pb)
Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
202Pb syn 5.25(28)×104 y ε 202Tl
204Pb1.4% stable
205Pb trace 1.73(7)×107 yε 205Tl
206Pb24.1%stable
207Pb22.1%stable
208Pb52.4%stable
209Pbtrace3.253(14) h β 209Bi
210Pbtrace22.3(22) yβ 210Bi
211Pbtrace36.1(2) minβ 211Bi
212Pbtrace10.64(1) hβ 212Bi
214Pbtrace26.8(9) minβ 214Bi
Isotopic abundances vary greatly by sample
Standard atomic weight Ar, standard(Pb)

Isotopes

Natural lead consists of four stable isotopes with mass numbers of 204, 206, 207, and 208, [30] and traces of five short-lived radioisotopes. [31] The high number of isotopes is consistent with lead's atomic number being even. [lower-alpha 8] Lead has a magic number of protons (82), for which the nuclear shell model accurately predicts an especially stable nucleus. [32] Lead-208 has 126 neutrons, another magic number, which may explain why lead-208 is extraordinarily stable. [32]

With its high atomic number, lead is the heaviest element whose natural isotopes are regarded as stable; lead-208 is the heaviest stable nucleus. (This distinction formerly fell to bismuth, with an atomic number of 83, until its only primordial isotope, bismuth-209, was found in 2003 to decay very slowly.) [lower-alpha 9] The four stable isotopes of lead could theoretically undergo alpha decay to isotopes of mercury with a release of energy, but this has not been observed for any of them; their predicted half-lives range from 1035 to 10189 years [35] (at least 1025 times the current age of the universe).

Three of the stable isotopes are found in three of the four major decay chains: lead-206, lead-207, and lead-208 are the final decay products of uranium-238, uranium-235, and thorium-232, respectively. [36] These decay chains are called the uranium chain, the actinium chain, and the thorium chain. [37] Their isotopic concentrations in a natural rock sample depends greatly on the presence of these three parent uranium and thorium isotopes. For example, the relative abundance of lead-208 can range from 52% in normal samples to 90% in thorium ores; [38] for this reason, the standard atomic weight of lead is given to only one decimal place. [39] As time passes, the ratio of lead-206 and lead-207 to lead-204 increases, since the former two are supplemented by radioactive decay of heavier elements while the latter is not; this allows for lead–lead dating. As uranium decays into lead, their relative amounts change; this is the basis for uranium–lead dating. [40] Lead-207 exhibits nuclear magnetic resonance, a property that has been used to study its compounds in solution and solid state, [41] [42] including in human body. [43]

The Holsinger meteorite, the largest piece of the Canyon Diablo meteorite. Uranium-lead dating and lead-lead dating on this meteorite allowed refinement of the age of the Earth to 4.55 billion +- 70 million years. Holsinger Meteorite.jpg
The Holsinger meteorite, the largest piece of the Canyon Diablo meteorite. Uranium–lead dating and lead–lead dating on this meteorite allowed refinement of the age of the Earth to 4.55 billion ± 70 million years.

Apart from the stable isotopes, which make up almost all lead that exists naturally, there are trace quantities of a few radioactive isotopes. One of them is lead-210; although it has a half-life of only 22.3 years, [30] small quantities occur in nature because lead-210 is produced by a long decay series that starts with uranium-238 (that has been present for billions of years on Earth). Lead-211, -212, and -214 are present in the decay chains of uranium-235, thorium-232, and uranium-238, respectively, so traces of all three of these lead isotopes are found naturally. Minute traces of lead-209 arise from the very rare cluster decay of radium-223, one of the daughter products of natural uranium-235, and the decay chain of neptunium-237, traces of which are produced by neutron capture in uranium ores. Lead-210 is particularly useful for helping to identify the ages of samples by measuring its ratio to lead-206 (both isotopes are present in a single decay chain). [44]

In total, 43 lead isotopes have been synthesized, with mass numbers 178–220. [30] Lead-205 is the most stable radioisotope, with a half-life of around 1.73×107 years. [lower-alpha 10] The second-most stable is lead-202, which has a half-life of about 52,500 years, longer than any of the natural trace radioisotopes. [30]

Chemistry

Flame test: lead colors flame pale blue FlammenfarbungPb.png
Flame test: lead colors flame pale blue

Bulk lead exposed to moist air forms a protective layer of varying composition. Lead(II) carbonate is a common constituent; [46] [47] [48] the sulfate or chloride may also be present in urban or maritime settings. [49] This layer makes bulk lead effectively chemically inert in the air. [49] Finely powdered lead, as with many metals, is pyrophoric, [50] and burns with a bluish-white flame. [51]

Fluorine reacts with lead at room temperature, forming lead(II) fluoride. The reaction with chlorine is similar but requires heating, as the resulting chloride layer diminishes the reactivity of the elements. [49] Molten lead reacts with the chalcogens to give lead(II) chalcogenides. [52]

Lead metal resists sulfuric and phosphoric acid but not hydrochloric or nitric acid; the outcome depends on insolubility and subsequent passivation of the product salt. [53] Organic acids, such as acetic acid, dissolve lead in the presence of oxygen. [49] Concentrated alkalis will dissolve lead and form plumbites. [54]

Inorganic compounds

Lead shows two main oxidation states: +4 and +2. The tetravalent state is common for the carbon group. The divalent state is rare for carbon and silicon, minor for germanium, important (but not prevailing) for tin, and is the more important of the two oxidation states for lead. [49] This is attributable to relativistic effects, specifically the inert pair effect, which manifests itself when there is a large difference in electronegativity between lead and oxide, halide, or nitride anions, leading to a significant partial positive charge on lead. The result is a stronger contraction of the lead 6s orbital than is the case for the 6p orbital, making it rather inert in ionic compounds. The inert pair effect is less applicable to compounds in which lead forms covalent bonds with elements of similar electronegativity, such as carbon in organolead compounds. In these, the 6s and 6p orbitals remain similarly sized and sp3 hybridization is still energetically favorable. Lead, like carbon, is predominantly tetravalent in such compounds. [55]

There is a relatively large difference in the electronegativity of lead(II) at 1.87 and lead(IV) at 2.33. This difference marks the reversal in the trend of increasing stability of the +4 oxidation state going down the carbon group; tin, by comparison, has values of 1.80 in the +2 oxidation state and 1.96 in the +4 state. [56]

Lead(II) oxide Oxid olovnaty.JPG
Lead(II) oxide

Lead(II)

Lead(II) compounds are characteristic of the inorganic chemistry of lead. Even strong oxidizing agents like fluorine and chlorine react with lead to give only PbF2 and PbCl2. [49] Lead(II) ions are usually colorless in solution, [57] and partially hydrolyze to form Pb(OH)+ and finally [Pb4(OH)4]4+ (in which the hydroxyl ions act as bridging ligands), [58] [59] but are not reducing agents as tin(II) ions are. Techniques for identifying the presence of the Pb2+ ion in water generally rely on the precipitation of lead(II) chloride using dilute hydrochloric acid. As the chloride salt is sparingly soluble in water, in very dilute solutions the precipitation of lead(II) sulfide is achieved by bubbling hydrogen sulfide through the solution. [60]

Lead monoxide exists in two polymorphs, litharge α-PbO (red) and massicot β-PbO (yellow), the latter being stable only above around 488 °C. Litharge is the most commonly used inorganic compound of lead. [61] There is no lead(II) hydroxide; increasing the pH of solutions of lead(II) salts leads to hydrolysis and condensation. [62] Lead commonly reacts with heavier chalcogens. Lead sulfide is a semiconductor, a photoconductor, and an extremely sensitive infrared radiation detector. The other two chalcogenides, lead selenide and lead telluride, are likewise photoconducting. They are unusual in that their color becomes lighter going down the group. [63]

Lead and oxygen in a tetragonal unit cell of lead(II,IV) oxide Red-lead-unit-cell-3D-balls.png
     Lead and      oxygen in a tetragonal unit cell of lead(II,IV) oxide

Lead dihalides are well-characterized; this includes the diastatide [64] and mixed halides, such as PbFCl. The relative insolubility of the latter forms a useful basis for the gravimetric determination of fluorine. The difluoride was the first solid ionically conducting compound to be discovered (in 1834, by Michael Faraday). [65] The other dihalides decompose on exposure to ultraviolet or visible light, especially the diiodide. [66] Many lead(II) pseudohalides are known, such as the cyanide, cyanate, and thiocyanate. [63] [67] Lead(II) forms an extensive variety of halide coordination complexes, such as [PbCl4]2−, [PbCl6]4−, and the [Pb2Cl9]n5n chain anion. [66]

Lead(II) sulfate is insoluble in water, like the sulfates of other heavy divalent cations. Lead(II) nitrate and lead(II) acetate are very soluble, and this is exploited in the synthesis of other lead compounds. [68]

Lead(IV)

Few inorganic lead(IV) compounds are known. They are only formed in highly oxidizing solutions and do not normally exist under standard conditions. [69] Lead(II) oxide gives a mixed oxide on further oxidation, Pb3O4. It is described as lead(II,IV) oxide, or structurally 2PbO·PbO2, and is the best-known mixed valence lead compound. Lead dioxide is a strong oxidizing agent, capable of oxidizing hydrochloric acid to chlorine gas. [70] This is because the expected PbCl4 that would be produced is unstable and spontaneously decomposes to PbCl2 and Cl2. [71] Analogously to lead monoxide, lead dioxide is capable of forming plumbate anions. Lead disulfide [72] and lead diselenide [73] are only stable at high pressures. Lead tetrafluoride, a yellow crystalline powder, is stable, but less so than the difluoride. Lead tetrachloride (a yellow oil) decomposes at room temperature, lead tetrabromide is less stable still, and the existence of lead tetraiodide is questionable. [74]

The capped square antiprismatic anion [Pb9] from [K(18-crown-6)]2K2Pb9*(en)1.5 Nonaplumbide-anion-from-xtal-3D-balls.png
The capped square antiprismatic anion [Pb9] from [K(18-crown-6)]2K2Pb9·(en)1.5

Other oxidation states

Some lead compounds exist in formal oxidation states other than +4 or +2. Lead(III) may be obtained, as an intermediate between lead(II) and lead(IV), in larger organolead complexes; this oxidation state is not stable, as both the lead(III) ion and the larger complexes containing it are radicals. [76] [77] [78] The same applies for lead(I), which can be found in such radical species. [79]

Numerous mixed lead(II,IV) oxides are known. When PbO2 is heated in air, it becomes Pb12O19 at 293 °C, Pb12O17 at 351 °C, Pb3O4 at 374 °C, and finally PbO at 605 °C. A further sesquioxide, Pb2O3, can be obtained at high pressure, along with several non-stoichiometric phases. Many of them show defective fluorite structures in which some oxygen atoms are replaced by vacancies: PbO can be considered as having such a structure, with every alternate layer of oxygen atoms absent. [80]

Negative oxidation states can occur as Zintl phases, as either free lead anions, as in Ba2Pb, with lead formally being lead(−IV), [81] or in oxygen-sensitive ring-shaped or polyhedral cluster ions such as the trigonal bipyramidal Pb52− ion, where two lead atoms are lead(−I) and three are lead(0). [82] In such anions, each atom is at a polyhedral vertex and contributes two electrons to each covalent bond along an edge from their sp3 hybrid orbitals, the other two being an external lone pair. [58] They may be made in liquid ammonia via the reduction of lead by sodium. [83]

Structure of a tetraethyllead molecule:
Carbon
Hydrogen
Lead Tetraethyllead-3D-balls.png
Structure of a tetraethyllead molecule:
     Carbon
     Hydrogen
     Lead

Organolead

Lead can form multiply-bonded chains, a property it shares with its lighter homologs in the carbon group. Its capacity to do so is much less because the Pb–Pb bond energy is over three and a half times lower than that of the C–C bond. [52] With itself, lead can build metal–metal bonds of an order up to three. [84] With carbon, lead forms organolead compounds similar to, but generally less stable than, typical organic compounds [85] (due to the Pb–C bond being rather weak). [58] This makes the organometallic chemistry of lead far less wide-ranging than that of tin. [86] Lead predominantly forms organolead(IV) compounds, even when starting with inorganic lead(II) reactants; very few organolead(II) compounds are known. The most well-characterized exceptions are Pb[CH(SiMe3)2]2 and Pb(η5-C5H5)2. [86]

The lead analog of the simplest organic compound, methane, is plumbane. Plumbane may be obtained in a reaction between metallic lead and atomic hydrogen. [87] Two simple derivatives, tetramethyllead and tetraethyllead, are the best-known organolead compounds. These compounds are relatively stable: tetraethyllead only starts to decompose if heated [88] or if exposed to sunlight or ultraviolet light. [89] (Tetraphenyllead is even more thermally stable, decomposing at 270 °C. [86] ) With sodium metal, lead readily forms an equimolar alloy that reacts with alkyl halides to form organometallic compounds such as tetraethyllead. [90] The oxidizing nature of many organolead compounds is usefully exploited: lead tetraacetate is an important laboratory reagent for oxidation in organic synthesis, [91] and tetraethyllead was once produced in larger quantities than any other organometallic compound. [86] Other organolead compounds are less chemically stable. [85] For many organic compounds, a lead analog does not exist. [87]

Origin and occurrence

Solar System abundances [92]
Atomic
number
ElementRelative
amount
42 Molybdenum 0.798
46 Palladium 0.440
50 Tin 1.146
78 Platinum 0.417
80 Mercury 0.127
82Lead1
90 Thorium 0.011
92 Uranium 0.003

In space

Lead's per-particle abundance in the Solar System is 0.121 ppb (parts per billion). [92] [lower-alpha 11] This figure is two and a half times higher than that of platinum, eight times more than mercury, and seventeen times more than gold. [92] The amount of lead in the universe is slowly increasing [93] as most heavier atoms (all of which are unstable) gradually decay to lead. [94] The abundance of lead in the Solar System since its formation 4.5 billion years ago has increased by about 0.75%. [95] The solar system abundances table shows that lead, despite its relatively high atomic number, is more prevalent than most other elements with atomic numbers greater than 40. [92]

Primordial lead—which comprises the isotopes lead-204, lead-206, lead-207, and lead-208—was mostly created as a result of repetitive neutron capture processes occurring in stars. The two main modes of capture are the s- and r-processes. [96]

In the s-process (s is for "slow"), captures are separated by years or decades, allowing less stable nuclei to undergo beta decay. [97] A stable thallium-203 nucleus can capture a neutron and become thallium-204; this undergoes beta decay to give stable lead-204; on capturing another neutron, it becomes lead-205, which has a half-life of around 15 million years. Further captures result in lead-206, lead-207, and lead-208. On capturing another neutron, lead-208 becomes lead-209, which quickly decays into bismuth-209. On capturing another neutron, bismuth-209 becomes bismuth-210, and this beta decays to polonium-210, which alpha decays to lead-206. The cycle hence ends at lead-206, lead-207, lead-208, and bismuth-209. [98]

Chart of the final part of the s-process, from mercury to polonium. Red lines and circles represent neutron captures; blue arrows represent beta decays; the green arrow represents an alpha decay; cyan arrows represent electron captures. S-R-processes-atomic-mass-201-to-210.svg
Chart of the final part of the s-process, from mercury to polonium. Red lines and circles represent neutron captures; blue arrows represent beta decays; the green arrow represents an alpha decay; cyan arrows represent electron captures.

In the r-process (r is for "rapid"), captures happen faster than nuclei can decay. [99] This occurs in environments with a high neutron density, such as a supernova or the merger of two neutron stars. The neutron flux involved may be on the order of 1022 neutrons per square centimeter per second. [100] The r-process does not form as much lead as the s-process. [101] It tends to stop once neutron-rich nuclei reach 126 neutrons. [102] At this point, the neutrons are arranged in complete shells in the atomic nucleus, and it becomes harder to energetically accommodate more of them. [103] When the neutron flux subsides, these nuclei beta decay into stable isotopes of osmium, iridium, and platinum. [104]

On Earth

Lead is classified as a chalcophile under the Goldschmidt classification, meaning it is generally found combined with sulfur. [105] It rarely occurs in its native, metallic form. [106] Many lead minerals are relatively light and, over the course of the Earth's history, have remained in the crust instead of sinking deeper into the Earth's interior. This accounts for lead's relatively high crustal abundance of 14 ppm; it is the 38th most abundant element in the crust. [107] [lower-alpha 12]

The main lead-bearing mineral is galena (PbS), which is mostly found with zinc ores. [109] Most other lead minerals are related to galena in some way; boulangerite, Pb5Sb4S11, is a mixed sulfide derived from galena; anglesite, PbSO4, is a product of galena oxidation; and cerussite or white lead ore, PbCO3, is a decomposition product of galena. Arsenic, tin, antimony, silver, gold, copper, and bismuth are common impurities in lead minerals. [109]

Lead is a fairly common element in the Earth's crust for its high atomic number (82). Most elements of atomic number greater than 40 are less abundant. Elemental abundances.svg
Lead is a fairly common element in the Earth's crust for its high atomic number (82). Most elements of atomic number greater than 40 are less abundant.

World lead resources exceed two billion tons. Significant deposits are located in Australia, China, Ireland, Mexico, Peru, Portugal, Russia, and the United States. Global reserves—resources that are economically feasible to extract—totaled 88 million tons in 2016, of which Australia had 35 million, China 17 million, and Russia 6.4 million. [110]

Typical background concentrations of lead do not exceed 0.1 μg/m3 in the atmosphere; 100 mg/kg in soil; and 5 μg/L in freshwater and seawater. [111]

Etymology

The modern English word "lead" is of Germanic origin; it comes from the Middle English leed and Old English lēad (with the macron above the "e" signifying that the vowel sound of that letter is long). [112] The Old English word is derived from the hypothetical reconstructed Proto-Germanic *lauda- ("lead"). [113] According to linguistic theory, this word bore descendants in multiple Germanic languages of exactly the same meaning. [113]

The origin of the Proto-Germanic *lauda- is not agreed in the linguistic community. One hypothesis suggests it is derived from Proto-Indo-European *lAudh- ("lead"; capitalization of the vowel is equivalent to the macron). [114] Another hypothesis suggests it is borrowed from Proto-Celtic *ɸloud-io- ("lead"). This word is related to the Latin plumbum, which gave the element its chemical symbol Pb. The word *ɸloud-io- is thought to be the origin of Proto-Germanic *bliwa- (which also means "lead"), from which stemmed the German Blei. [115]

The name of the chemical element is not related to the verb of the same spelling, which is derived from Proto-Germanic *laidijan- ("to lead"). [116]

History

World lead production peaking in the Roman period and the Industrial Revolution. Lead production graph.svg
World lead production peaking in the Roman period and the Industrial Revolution.

Prehistory and early history

Metallic lead beads dating back to 7000–6500 BCE have been found in Asia Minor and may represent the first example of metal smelting. [118] At that time lead had few (if any) applications due to its softness and dull appearance. [118] The major reason for the spread of lead production was its association with silver, which may be obtained by burning galena (a common lead mineral). [119] The Ancient Egyptians were the first to use lead minerals in cosmetics, an application that spread to Ancient Greece and beyond; [120] the Egyptians may have used lead for sinkers in fishing nets, glazes, glasses, enamels, and for ornaments. [119] Various civilizations of the Fertile Crescent used lead as a writing material, as currency, and as a construction material. [119] Lead was used in the Ancient Chinese royal court as a stimulant, [119] as currency, [121] and as a contraceptive; [122] the Indus Valley civilization and the Mesoamericans [119] used it for making amulets; and the eastern and southern African peoples used lead in wire drawing. [123]

Classical era

Because silver was extensively used as a decorative material and an exchange medium, lead deposits came to be worked in Asia Minor from 3000 BCE; later, lead deposits were developed in the Aegean and Laurion. These three regions collectively dominated production of mined lead until c. 1200 BCE. [124] Beginning circa 2000 BCE, the Phoenicians worked deposits in the Iberian peninsula; by 1600 BCE, lead mining existed in Cyprus, Greece, and Sardinia. [125]

Ancient Greek lead sling bullets with a winged thunderbolt molded on one side and the inscription "DEKsAI" ("take that" or "catch") on the other side Sling bullets BM GR1842.7-28.550 GR1851.5-7.11.jpg
Ancient Greek lead sling bullets with a winged thunderbolt molded on one side and the inscription "ΔΕΞΑΙ" ("take that" or "catch") on the other side

Rome's territorial expansion in Europe and across the Mediterranean, and its development of mining, led to it becoming the greatest producer of lead during the classical era, with an estimated annual output peaking at 80,000 tonnes. Like their predecessors, the Romans obtained lead mostly as a by-product of silver smelting. [117] [127] Lead mining occurred in Central Europe, Britain, the Balkans, Greece, Anatolia, and Hispania, the latter accounting for 40% of world production. [117]

Lead tablets were commonly used as a material for letters. [128] Lead coffins, cast in flat sand forms, with interchangeable motifs to suit the faith of the deceased were used in ancient Judea. [129] Lead was used to make slings bullet from the 5th century BC. In Roman times, lead sling bullets were amply used, and were effective at a distance of between 100 and 150 meters. The Balearic slingers, used as mercenaries in Carthaginian and Roman armies, were famous for their shooting distance and accuracy. [130]

Lead was used for making water pipes in the Roman Empire; the Latin word for the metal, plumbum, is the origin of the English word "plumbing". Its ease of working and resistance to corrosion [131] ensured its widespread use in other applications, including pharmaceuticals, roofing, currency, and warfare. [132] [133] [134] Writers of the time, such as Cato the Elder, Columella, and Pliny the Elder, recommended lead (or lead-coated) vessels for the preparation of sweeteners and preservatives added to wine and food. The lead conferred an agreeable taste due to the formation of "sugar of lead" (lead(II) acetate), whereas copper or bronze vessels could impart a bitter flavor through verdigris formation. [135]

This metal was by far the most used material in classical antiquity, and it is appropriate to refer to the (Roman) Lead Age. Lead was to the Romans what plastic is to us.

Heinz Eschnauer and Markus Stoeppler
"Wine—An enological specimen bank", 1992 [136]

The Roman author Vitruvius reported the health dangers of lead [137] and modern writers have suggested that lead poisoning played a major role in the decline of the Roman Empire. [138] [139] [lower-alpha 13] Other researchers have criticized such claims, pointing out, for instance, that not all abdominal pain is caused by lead poisoning. [141] [142] According to archaeological research, Roman lead pipes increased lead levels in tap water but such an effect was "unlikely to have been truly harmful". [143] [144] When lead poisoning did occur, victims were called "saturnine", dark and cynical, after the ghoulish father of the gods, Saturn. By association, lead was considered the father of all metals. [145] Its status in Roman society was low as it was readily available [146] and cheap. [147]

Roman lead pipes Grosvenor Museums - Wasserrohren.jpg
Roman lead pipes

Confusion with tin and antimony

During the classical era (and even up to the 17th century), tin was often not distinguished from lead: Romans called lead plumbum nigrum ("black lead"), and tin plumbum candidum ("bright lead"). The association of lead and tin can be seen in other languages: the word olovo in Czech translates to "lead", but in Russian, its cognate олово (olovo) means "tin". [148] To add to the confusion, lead bore a close relation to antimony: both elements commonly occur as sulfides (galena and stibnite), often together. Pliny incorrectly wrote that stibnite would give lead on heating, instead of antimony. [149] In countries such as Turkey and India, the originally Persian name surma came to refer to either antimony sulfide or lead sulfide, [150] and in some languages, such as Russian, gave its name to antimony (сурьма). [151]

Middle Ages and the Renaissance

Lead mining in Western Europe declined after the fall of the Western Roman Empire, with Arabian Iberia being the only region having a significant output. [152] [153] The largest production of lead occurred in South and East Asia, especially China and India, where lead mining grew rapidly. [153]

Elizabeth I of England was commonly depicted with a whitened face. Lead in face whiteners is thought to have contributed to her death. Nicholas Hilliard (called) - Portrait of Queen Elizabeth I - Google Art Project.jpg
Elizabeth I of England was commonly depicted with a whitened face. Lead in face whiteners is thought to have contributed to her death.

In Europe, lead production began to increase in the 11th and 12th centuries, when it was again used for roofing and piping. Starting in the 13th century, lead was used to create stained glass. [155] In the European and Arabian traditions of alchemy, lead (symbol Saturn symbol.svg in the European tradition) [156] was considered an impure base metal which, by the separation, purification and balancing of its constituent essences, could be transformed to pure and incorruptible gold. [157] During the period, lead was used increasingly for adulterating wine. The use of such wine was forbidden for use in Christian rites by a papal bull in 1498, but it continued to be imbibed and resulted in mass poisonings up to the late 18th century. [152] [158] Lead was a key material in parts of the printing press, which was invented around 1440; lead dust was commonly inhaled by print workers, causing lead poisoning. [159] Firearms were invented at around the same time, and lead, despite being more expensive than iron, became the chief material for making bullets. It was less damaging to iron gun barrels, had a higher density (which allowed for better retention of velocity), and its lower melting point made the production of bullets easier as they could be made using a wood fire. [160] Lead, in the form of Venetian ceruse, was extensively used in cosmetics by Western European aristocracy as whitened faces were regarded as a sign of modesty. [161] [162] This practice later expanded to white wigs and eyeliners, and only faded out with the French Revolution in the late 18th century. A similar fashion appeared in Japan in the 18th century with the emergence of the geishas, a practice that continued long into the 20th century. The white faces of women "came to represent their feminine virtue as Japanese women", [163] with lead commonly used in the whitener. [164]

Outside Europe and Asia

In the New World, lead production was recorded soon after the arrival of European settlers. The earliest record dates to 1621 in the English Colony of Virginia, fourteen years after its foundation. [165] In Australia, the first mine opened by colonists on the continent was a lead mine, in 1841. [166] In Africa, lead mining and smelting were known in the Benue Trough [167] and the lower Congo Basin, where lead was used for trade with Europeans, and as a currency by the 17th century, [168] well before the scramble for Africa.

Lead mining in the upper Mississippi River region in the United States in 1865 Lead mining Barber 1865p321cropped.jpg
Lead mining in the upper Mississippi River region in the United States in 1865

Industrial Revolution

In the second half of the 18th century, Britain, and later continental Europe and the United States, experienced the Industrial Revolution. This was the first time during which lead production rates exceeded those of Rome. [117] Britain was the leading producer, losing this status by the mid-19th century with the depletion of its mines and the development of lead mining in Germany, Spain, and the United States. [169] By 1900, the United States was the leader in global lead production, and other non-European nations—Canada, Mexico, and Australia—had begun significant production; production outside Europe exceeded that within. [170] A great share of the demand for lead came from plumbing and painting—lead paints were in regular use. [171] At this time, more (working class) people were exposed to the metal and lead poisoning cases escalated. This led to research into the effects of lead intake. Lead was proven to be more dangerous in its fume form than as a solid metal. Lead poisoning and gout were linked; British physician Alfred Baring Garrod noted a third of his gout patients were plumbers and painters. The effects of chronic ingestion of lead, including mental disorders, were also studied in the 19th century. The first laws aimed at decreasing lead poisoning in factories were enacted during the 1870s and 1880s in the United Kingdom. [171]

Promotional poster for Dutch Boy lead paint, United States, 1912 Dutch boy collier white lead.png
Promotional poster for Dutch Boy lead paint, United States, 1912

Modern era

Further evidence of the threat that lead posed to humans was discovered in the late 19th and early 20th centuries. Mechanisms of harm were better understood, lead blindness was documented, and the element was phased out of public use in the United States and Europe. The United Kingdom introduced mandatory factory inspections in 1878 and appointed the first Medical Inspector of Factories in 1898; as a result, a 25-fold decrease in lead poisoning incidents from 1900 to 1944 was reported. [172] Most European countries banned lead paint—commonly used because of its opacity and water resistance [173] —for interiors by 1930. [174]

The last major human exposure to lead was the addition of tetraethyllead to gasoline as an antiknock agent, a practice that originated in the United States in 1921. It was phased out in the United States and the European Union by 2000. [171]

In the 1970s, the United States and Western European countries introduced legislation to reduce lead air pollution. [175] [176] The impact was significant: while a study conducted by the Centers for Disease Control and Prevention in the United States in 1976–1980 showed that 77.8% of the population had elevated blood lead levels, in 1991–1994, a study by the same institute showed the share of people with such high levels dropped to 2.2%. [177] The main product made of lead by the end of the 20th century was the lead–acid battery,. [178]

From 1960 to 1990, lead output in the Western Bloc grew by about 31%. [179] The share of the world's lead production by the Eastern Bloc increased from 10% to 30%, from 1950 to 1990, with the Soviet Union being the world's largest producer during the mid-1970s and the 1980s, and China starting major lead production in the late 20th century. [180] Unlike the European communist countries, China was largely unindustrialized by the mid-20th century; in 2004, China surpassed Australia as the largest producer of lead. [181] As was the case during European industrialization, lead has had a negative effect on health in China. [182]

Production

Primary production of lead since 1840 Evolution production plomb.svg
Primary production of lead since 1840

As of 2014, production of lead is increasing worldwide due to its use in lead–acid batteries. [183] There are two major categories of production: primary from mined ores, and secondary from scrap. In 2014, 4.58 million metric tons came from primary production and 5.64 million from secondary production. The top three producers of mined lead concentrate in that year were China, Australia, and the United States. [110] The top three producers of refined lead were China, the United States, and India. [184] According to the International Resource Panel's Metal Stocks in Society report of 2010, the total amount of lead in use, stockpiled, discarded, or dissipated into the environment, on a global basis, is 8 kg per capita. Much of this is in more developed countries (20–150 kg per capita) rather than less developed ones (1–4 kg per capita). [185]

The primary and secondary lead production processes are similar. Some primary production plants now supplement their operations with scrap lead, and this trend is likely to increase in the future. Given adequate techniques, lead obtained via secondary processes is indistinguishable from lead obtained via primary processes. Scrap lead from the building trade is usually fairly clean and is re-melted without the need for smelting, though refining is sometimes needed. Secondary lead production is therefore cheaper, in terms of energy requirements, than is primary production, often by 50% or more. [186]

Primary

Most lead ores contain a low percentage of lead (rich ores have a typical content of 3–8%) which must be concentrated for extraction. [187] During initial processing, ores typically undergo crushing, dense-medium separation, grinding, froth flotation, and drying. The resulting concentrate, which has a lead content of 30–80% by mass (regularly 50–60%), [187] is then turned into (impure) lead metal.

There are two main ways of doing this: a two-stage process involving roasting followed by blast furnace extraction, carried out in separate vessels; or a direct process in which the extraction of the concentrate occurs in a single vessel. The latter has become the most common route, though the former is still significant. [188]

World's largest mining countries of lead, 2016 [110]
CountryOutput
(thousand
tons)
Flag of the People's Republic of China.svg China2,400
Flag of Australia (converted).svg Australia500
Flag of the United States.svg United States335
Flag of Peru.svg Peru310
Flag of Mexico.svg Mexico250
Flag of Russia.svg Russia225
Flag of India.svg India135
Flag of Bolivia.svg Bolivia80
Flag of Sweden.svg Sweden76
Flag of Turkey.svg Turkey75
Flag of Iran.svg Iran41
Flag of Kazakhstan.svg Kazakhstan41
Flag of Poland.svg Poland40
Flag of South Africa.svg South Africa40
Flag of North Korea.svg North Korea35
Flag of Ireland.svg Ireland33
Flag of North Macedonia.svg Macedonia33
Other countries170

Two-stage process

First, the sulfide concentrate is roasted in air to oxidize the lead sulfide: [189]

2 PbS(s) + 3 O2(g) → 2 PbO(s) + 2 SO2(g)↑

As the original concentrate was not pure lead sulfide, roasting yields not only the desired lead(II) oxide, but a mixture of oxides, sulfates, and silicates of lead and of the other metals contained in the ore. [190] This impure lead oxide is reduced in a coke-fired blast furnace to the (again, impure) metal: [191]

2 PbO(s) + C(s) → 2 Pb(s) + CO2(g)↑

Impurities are mostly arsenic, antimony, bismuth, zinc, copper, silver, and gold. Typically they are removed in a series of pyrometallurgical processes. The melt is treated in a reverberatory furnace with air, steam, and sulfur, which oxidizes the impurities except for silver, gold, and bismuth. Oxidized contaminants float to the top of the melt and are skimmed off. [192] [193] Metallic silver and gold are removed and recovered economically by means of the Parkes process, in which zinc is added to lead. Zinc, which is immiscible in lead, dissolves the silver and gold. The zinc solution can be separated from the lead, and the silver and gold retrieved. [193] [194] De-silvered lead is freed of bismuth by the Betterton–Kroll process, treating it with metallic calcium and magnesium. The resulting bismuth dross can be skimmed off. [193]

Alternatively to the pyrometallurgical processes, very pure lead can be obtained by processing smelted lead electrolytically using the Betts process. Anodes of impure lead and cathodes of pure lead are placed in an electrolyte of lead fluorosilicate (PbSiF6). Once electrical potential is applied, impure lead at the anode dissolves and plates onto the cathode, leaving the majority of the impurities in solution. [193] [195] This is a high-cost process and thus mostly reserved for refining bullion containing high percentages of impurities. [196]

Direct process

In this process, lead bullion and slag is obtained directly from lead concentrates. The lead sulfide concentrate is melted in a furnace and oxidized, forming lead monoxide. Carbon (as coke or coal gas [lower-alpha 15] ) is added to the molten charge along with fluxing agents. The lead monoxide is thereby reduced to metallic lead, in the midst of a slag rich in lead monoxide. [188]

If the input is rich in lead, as much as 80% of the original lead can be obtained as bullion; the remaining 20% forms a slag rich in lead monoxide. For a low-grade feed, all of the lead can be oxidized to a high-lead slag. [188] Metallic lead is further obtained from the high-lead (25–40%) slags via submerged fuel combustion or injection, reduction assisted by an electric furnace, or a combination of both. [188]

Alternatives

Research on a cleaner, less energy-intensive lead extraction process continues; a major drawback is that either too much lead is lost as waste, or the alternatives result in a high sulfur content in the resulting lead metal. Hydrometallurgical extraction, in which anodes of impure lead are immersed into an electrolyte and pure lead is deposited onto a cathode, is a technique that may have potential, but is not currently economical except in cases where electricity is very cheap. [197]

Secondary

Smelting, which is an essential part of the primary production, is often skipped during secondary production. It is only performed when metallic lead has undergone significant oxidation. [186] The process is similar to that of primary production in either a blast furnace or a rotary furnace, with the essential difference being the greater variability of yields: blast furnaces produce hard lead (10% antimony) while reverberatory and rotary kiln furnaces produced semisoft lead (3–4% antimony). [198] The Isasmelt process is a more recent smelting method that may act as an extension to primary production; battery paste from spent lead–acid batteries (containing lead sulfate and lead oxides) has its sulfate removed by treating it with alkali, and is then treated in a coal-fueled furnace in the presence of oxygen, which yields impure lead, with antimony the most common impurity. [199] Refining of secondary lead is similar to that of primary lead; some refining processes may be skipped depending on the material recycled and its potential contamination. [199]

Of the sources of lead for recycling, lead–acid batteries are the most important; lead pipe, sheet, and cable sheathing are also significant. [186]

Applications

Bricks of lead (alloyed with 4% antimony) are used as radiation shielding. Lead shielding.jpg
Bricks of lead (alloyed with 4% antimony) are used as radiation shielding.

Contrary to popular belief, pencil leads in wooden pencils have never been made from lead. When the pencil originated as a wrapped graphite writing tool, the particular type of graphite used was named plumbago (literally, act for lead or lead mockup). [201]

Elemental form

Lead metal has several useful mechanical properties, including high density, low melting point, ductility, and relative inertness. Many metals are superior to lead in some of these aspects but are generally less common and more difficult to extract from parent ores. Lead's toxicity has led to its phasing out for some uses. [202]

Lead has been used for bullets since their invention in the Middle Ages. It is inexpensive; its low melting point means small arms ammunition and shotgun pellets can be cast with minimal technical equipment; and it is denser than other common metals, which allows for better retention of velocity. It remains the main material for bullets, alloyed with other metals as hardeners. [160] Concerns have been raised that lead bullets used for hunting can damage the environment. [lower-alpha 16]

Lead's high density and resistance to corrosion have been exploited in a number of related applications. It is used as ballast in sailboat keels; its density allows it to take up a small volume and minimize water resistance, thus counterbalancing the heeling effect of wind on the sails. [204] It is used in scuba diving weight belts to counteract the diver's buoyancy. [205] In 1993, the base of the Leaning Tower of Pisa was stabilized with 600 tonnes of lead. [206] Because of its corrosion resistance, lead is used as a protective sheath for underwater cables. [207]

A 17th-century gold-coated lead sculpture Parc de Versailles, Bassin de Flore, Jean-Baptiste Tuby (1672-79) 07.jpg
A 17th-century gold-coated lead sculpture

Lead has many uses in the construction industry; lead sheets are used as architectural metals in roofing material, cladding, flashing, gutters and gutter joints, and on roof parapets. [208] [209] Lead is still used in statues and sculptures, [lower-alpha 17] including for armatures. [211] In the past it was often used to balance the wheels of cars; for environmental reasons this use is being phased out in favor of other materials. [110]

Lead is added to copper alloys, such as brass and bronze, to improve machinability and for its lubricating qualities. Being practically insoluble in copper the lead forms solid globules in imperfections throughout the alloy, such as grain boundaries. In low concentrations, as well as acting as a lubricant, the globules hinder the formation of swarf as the alloy is worked, thereby improving machinability. Copper alloys with larger concentrations of lead are used in bearings. The lead provides lubrication, and the copper provides the load-bearing support. [212]

Lead's high density, atomic number, and formability form the basis for use of lead as a barrier that absorbs sound, vibration, and radiation. [213] Lead has no natural resonance frequencies; [213] as a result, sheet-lead is used as a sound deadening layer in the walls, floors, and ceilings of sound studios. [214] Organ pipes are often made from a lead alloy, mixed with various amounts of tin to control the tone of each pipe. [215] [216] Lead is an established shielding material from radiation in nuclear science and in X-ray rooms [217] due to its denseness and high attenuation coefficient. [218] Molten lead has been used as a coolant for lead-cooled fast reactors. [219]

The largest use of lead in the early 21st century is in lead–acid batteries. The lead in batteries undergoes no direct contact with humans, so there are fewer toxicity concerns. [lower-alpha 18] People who work in battery production plants may be exposed to lead dust and inhale it. [221] } The reactions in the battery between lead, lead dioxide, and sulfuric acid provide a reliable source of voltage. [lower-alpha 19] Supercapacitors incorporating lead–acid batteries have been installed in kilowatt and megawatt scale applications in Australia, Japan, and the United States in frequency regulation, solar smoothing and shifting, wind smoothing, and other applications. [223] These batteries have lower energy density and charge-discharge efficiency than lithium-ion batteries, but are significantly cheaper. [224]

Lead glass Crystal glass.jpg
Lead glass

Lead is used in high voltage power cables as sheathing material to prevent water diffusion into insulation; this use is decreasing as lead is being phased out. [225] Its use in solder for electronics is also being phased out by some countries to reduce the amount of environmentally hazardous waste. [226] Lead is one of three metals used in the Oddy test for museum materials, helping detect organic acids, aldehydes, and acidic gases. [227] [228]

Compounds

In addition to being the main application for lead metal, lead-acid batteries are also the main consumer of lead compounds. The energy storage/release reaction used in these devices involves lead sulfate and lead dioxide:

Pb(s) + PbO
2
(s) + 2H
2
SO
4
(aq) → 2PbSO
4
(s) + 2H
2
O
(l)

Other applications of lead compounds are very specialized and often fading. Lead-based coloring agents are used in ceramic glazes and glass, especially for red and yellow shades. [229] While lead paints are phased out in Europe and North America, they remain in use in less developed countries such as China, [230] India, [231] or Indonesia. [232] Lead tetraacetate and lead dioxide are used as oxidizing agents in organic chemistry. Lead is frequently used in the polyvinyl chloride coating of electrical cords. [233] [234] It can be used to treat candle wicks to ensure a longer, more even burn. Because of its toxicity, European and North American manufacturers use alternatives such as zinc. [235] [236] Lead glass is composed of 12–28% lead oxide, changing its optical characteristics and reducing the transmission of ionizing radiation. [237] Lead-based semiconductors such as lead telluride and lead selenide are used in photovoltaic cells and infrared detectors. [238]

Biological effects

Lead
Hazards
GHS pictograms GHS-pictogram-exclam.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg
GHS signal word Danger
H302, H332, H351, H360Df, H373, H410
P201, P261, P273, P304, P340, P312, P308, P313, P391 [239]
NFPA 704
Flammability code 0: Will not burn. E.g. waterHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeLead
0
2
0

Lead has no confirmed biological role, and there is no confirmed safe level of lead exposure. [240] A 2009 Canadian–American study concluded that even at levels that are considered to pose little to no risk, lead may cause "adverse mental health outcomes". [241] Its prevalence in the human body—at an adult average of 120 mg [lower-alpha 20] —is nevertheless exceeded only by zinc (2500 mg) and iron (4000 mg) among the heavy metals. [243] Lead salts are very efficiently absorbed by the body. [244] A small amount of lead (1%) is stored in bones; the rest is excreted in urine and feces within a few weeks of exposure. Only about a third of lead is excreted by a child. Continual exposure may result in the bioaccumulation of lead. [245]

Toxicity

Lead is a highly poisonous metal (whether inhaled or swallowed), affecting almost every organ and system in the human body. [246] At airborne levels of 100 mg/m3, it is immediately dangerous to life and health. [247] Most ingested lead is absorbed into the bloodstream. [248] The primary cause of its toxicity is its predilection for interfering with the proper functioning of enzymes. It does so by binding to the sulfhydryl groups found on many enzymes, [249] or mimicking and displacing other metals which act as cofactors in many enzymatic reactions. [250] Among the essential metals that lead interacts with are calcium, iron, and zinc. [251] High levels of calcium and iron tend to provide some protection from lead poisoning; low levels cause increased susceptibility. [244]

Effects

Lead can cause severe damage to the brain and kidneys and, ultimately, death. By mimicking calcium, lead can cross the blood–brain barrier. It degrades the myelin sheaths of neurons, reduces their numbers, interferes with neurotransmission routes, and decreases neuronal growth. [249] In the human body, lead inhibits porphobilinogen synthase and ferrochelatase, preventing both porphobilinogen formation and the incorporation of iron into protoporphyrin IX, the final step in heme synthesis. This causes ineffective heme synthesis and microcytic anemia. [252]

Symptoms of lead poisoning Symptoms of lead poisoning (raster).png
Symptoms of lead poisoning

Symptoms of lead poisoning include nephropathy, colic-like abdominal pains, and possibly weakness in the fingers, wrists, or ankles. Small blood pressure increases, particularly in middle-aged and older people, may be apparent and can cause anemia. Several studies, mostly cross-sectional, found an association between increased lead exposure and decreased heart rate variability. [253] In pregnant women, high levels of exposure to lead may cause miscarriage. Chronic, high-level exposure has been shown to reduce fertility in males. [254]

In a child's developing brain, lead interferes with synapse formation in the cerebral cortex, neurochemical development (including that of neurotransmitters), and the organization of ion channels. [255] Early childhood exposure has been linked with an increased risk of sleep disturbances and excessive daytime drowsiness in later childhood. [256] High blood levels are associated with delayed puberty in girls. [257] The rise and fall in exposure to airborne lead from the combustion of tetraethyl lead in gasoline during the 20th century has been linked with historical increases and decreases in crime levels, a hypothesis which is not universally accepted. [258]

Exposure sources

Lead exposure is a global issue since lead mining and smelting, and battery manufacturing/disposal/recycling, are common in many countries. Lead enters the body via inhalation, ingestion, or skin absorption. Almost all inhaled lead is absorbed into the body; for ingestion, the rate is 20–70%, with children absorbing a higher percentage than adults. [259]

Poisoning typically results from ingestion of food or water contaminated with lead, and less commonly after accidental ingestion of contaminated soil, dust, or lead-based paint. [260] Seawater products can contain lead if affected by nearby industrial waters. [261] Fruit and vegetables can be contaminated by high levels of lead in the soils they were grown in. Soil can be contaminated through particulate accumulation from lead in pipes, lead paint, and residual emissions from leaded gasoline. [262]

The use of lead for water pipes is a problem in areas with soft or acidic water. [263] Hard water forms insoluble layers in the pipes whereas soft and acidic water dissolves the lead pipes. [264] Dissolved carbon dioxide in the carried water may result in the formation of soluble lead bicarbonate; oxygenated water may similarly dissolve lead as lead(II) hydroxide. Drinking such water, over time, can cause health problems due to the toxicity of the dissolved lead. The harder the water the more calcium bicarbonate and sulfate it will contain, and the more the inside of the pipes will be coated with a protective layer of lead carbonate or lead sulfate. [265]

Kymographic recording of the effect of lead acetate on frog heart experimental set up. Kymographic recording of the effect of lead on frog heart..jpg
Kymographic recording of the effect of lead acetate on frog heart experimental set up.

Ingestion of applied lead-based paint is the major source of exposure for children: a direct source is chewing on old painted window sills. Alternatively, as the applied dry paint deteriorates, it peels, is pulverized into dust and then enters the body through hand-to-mouth contact or contaminated food, water, or alcohol. Ingesting certain home remedies may result in exposure to lead or its compounds. [266]

Inhalation is the second major exposure pathway, affecting smokers and especially workers in lead-related occupations. [248] Cigarette smoke contains, among other toxic substances, radioactive lead-210. [267]

Skin exposure may be significant for people working with organic lead compounds. The rate of skin absorption is lower for inorganic lead. [268]

Treatment

Treatment for lead poisoning normally involves the administration of dimercaprol and succimer. [269] Acute cases may require the use of disodium calcium edetate, the calcium chelate, and the disodium salt of ethylenediaminetetraacetic acid (EDTA). It has a greater affinity for lead than calcium, with the result that lead chelate is formed by exchange and excreted in the urine, leaving behind harmless calcium. [270]

Environmental effects

Battery collection site in Dakar, Senegal, where at least 18 children died of lead poisoning in 2008 Batteries at Thiaroye.jpg
Battery collection site in Dakar, Senegal, where at least 18 children died of lead poisoning in 2008

The extraction, production, use, and disposal of lead and its products have caused significant contamination of the Earth's soils and waters. Atmospheric emissions of lead were at their peak during the Industrial Revolution, and the leaded gasoline period in the second half of the twentieth century. Lead releases originate from natural sources (i.e., concentration of the naturally occurring lead), industrial production, incineration and recycling, and mobilization of previously buried lead. [271] Elevated concentrations of lead persist in soils and sediments in post-industrial and urban areas; industrial emissions, including those arising from coal burning, [272] continue in many parts of the world, particularly in the developing countries. [273]

Lead can accumulate in soils, especially those with a high organic content, where it remains for hundreds to thousands of years. Environmental lead can compete with other metals found in and on plants surfaces potentially inhibiting photosynthesis and at high enough concentrations, negatively affecting plant growth and survival. Contamination of soils and plants can allow lead to ascend the food chain affecting microorganisms and animals. In animals, lead exhibits toxicity in many organs, damaging the nervous, renal, reproductive, hematopoietic, and cardiovascular systems after ingestion, inhalation, or skin absorption. [274] Fish uptake lead from both water and sediment; [275] bioaccumulation in the food chain poses a hazard to fish, birds, and sea mammals. [276]

Anthropogenic lead includes lead from shot and sinkers. These are among the most potent sources of lead contamination along with lead production sites. [277] Lead was banned for shot and sinkers in the United States in 2017, [278] although that ban was only effective for a month, [279] and a similar ban is being considered in the European Union. [280]

Analytical methods for the determination of lead in the environment include spectrophotometry, X-ray fluorescence, atomic spectroscopy and electrochemical methods. A specific ion-selective electrode has been developed based on the ionophore S,S'-methylenebis(N,N-diisobutyldithiocarbamate). [281] An important biomarker assay for lead poisoning is δ-aminolevulinic acid levels in plasma, serum, and urine. [282]

Restriction and remediation

Radiography of a swan found dead in Conde-sur-l'Escaut (northern France), highlighting lead shot. There are hundreds of lead pellets; a dozen is enough to kill an adult swan within a few days. Such bodies are sources of environmental contamination by lead. 1plombs chasse cygne conde2.jpg
Radiography of a swan found dead in Condé-sur-l'Escaut (northern France), highlighting lead shot. There are hundreds of lead pellets; a dozen is enough to kill an adult swan within a few days. Such bodies are sources of environmental contamination by lead.

By the mid-1980s, there was significant decline in the use of lead in industry. In the United States, environmental regulations reduced or eliminated the use of lead in non-battery products, including gasoline, paints, solders, and water systems. Particulate control devices were installed in coal-fired power plants to capture lead emissions. [272] In 1992, U.S. Congress required the Environmental Protection Agency to reduce the blood lead levels of the country's children. [283] Lead use was further curtailed by the European Union's 2003 Restriction of Hazardous Substances Directive. [284] A large drop in lead deposition occurred in the Netherlands after the 1993 national ban on use of lead shot for hunting and sport shooting: from 230 tonnes in 1990 to 47.5 tonnes in 1995. [285]

In the United States, the permissible exposure limit for lead in the workplace, comprising metallic lead, inorganic lead compounds, and lead soaps, was set at 50 μg/m3 over an 8-hour workday, and the blood lead level limit at 5 μg per 100 g of blood in 2012. [286] Lead may still be found in harmful quantities in stoneware, [287] vinyl [288] (such as that used for tubing and the insulation of electrical cords), and Chinese brass. [lower-alpha 21] Old houses may still contain lead paint. [288] White lead paint has been withdrawn from sale in industrialized countries, but specialized uses of other pigments such as yellow lead chromate remain. [173] Stripping old paint by sanding produces dust which can be inhaled. [290] Lead abatement programs have been mandated by some authorities in properties where young children live. [291]

Lead waste, depending on the jurisdiction and the nature of the waste, may be treated as household waste (in order to facilitate lead abatement activities), [292] or potentially hazardous waste requiring specialized treatment or storage. [293] Lead is released to the wildlife in shooting places and a number of lead management practices, such as stewardship of the environment and reduced public scrutiny, have been developed to counter the lead contamination. [294] Lead migration can be enhanced in acidic soils; to counter that, it is advised soils be treated with lime to neutralize the soils and prevent leaching of lead. [295]

Research has been conducted on how to remove lead from biosystems by biological means: Fish bones are being researched for their ability to bioremediate lead in contaminated soil. [296] [297] The fungus Aspergillus versicolor is effective at absorbing lead ions from industrial waste before being released to water bodies. [298] Several bacteria have been researched for their ability to remove lead from the environment, including the sulfate-reducing bacteria Desulfovibrio and Desulfotomaculum , both of which are highly effective in aqueous solutions. [299]

See also

Notes

  1. About 10% of the lanthanide contraction has been attributed to relativistic effects. [4]
  2. The tetrahedral allotrope of tin is called α- or gray tin and is stable only at or below 13.2 °C (55.8 °F). The stable form of tin above this temperature is called β- or white tin and has a distorted face centered cubic (tetragonal) structure which can be derived by compressing the tetrahedra of gray tin along their cubic axes. White tin effectively has a structure intermediate between the regular tetrahedral structure of gray tin, and the regular face centered cubic structure of lead, consistent with the general trend of increasing metallic character going down any representative group. [10]
  3. A quasicrystalline thin-film allotrope of lead, with pentagonal symmetry, was reported in 2013. The allotrope was obtained by depositing lead atoms on the surface of an icosahedral silver-indium-ytterbium quasicrystal. Its conductivity was not recorded. [11] [12]
  4. Diamond cubic structures with lattice parameters around the lattice parameter of silicon exists both in thin lead and tin films, and in massive lead and tin, freshly solidified in vacuum of ~5 x 10−6 Torr. Experimental evidence for almost identical structures of at least three oxide types is presented, demonstrating that lead and tin behave like silicon not only in the initial stages of crystallization, but also in the initial stages of oxidation. [13]
  5. British English: to go down like a lead balloon.
  6. Malleability describes how easily it deforms under compression, whereas ductility means its ability to stretch.
  7. A (wet) finger can be dipped into molten lead without risk of a burning injury. [26]
  8. An even number of either protons or neutrons generally increases the nuclear stability of isotopes, compared to isotopes with odd numbers. No elements with odd atomic numbers have more than two stable isotopes; even-numbered elements have multiple stable isotopes, with tin (element 50) having the highest number of isotopes of all elements, ten. [30] See Even and odd atomic nuclei for more details.
  9. The half-life found in the experiment was 1.9×1019 years. [33] A kilogram of natural bismuth would have an activity value of approximately 0.003 becquerels (decays per second). For comparison, the activity value of natural radiation in the human body is around 65 becquerels per kilogram of body weight (4500 becquerels on average). [34]
  10. Lead-205 decays solely via electron capture, which means when there are no electrons available and lead is fully ionized with all 82 electrons removed it cannot decay. Fully ionized thallium-205, the isotope lead-205 would decay to, becomes unstable and can decay into a bound state of lead-205. [45]
  11. Abundances in the source are listed relative to silicon rather than in per-particle notation. The sum of all elements per 106 parts of silicon is 2.6682×1010 parts; lead comprises 3.258 parts.
  12. Elemental abundance figures are estimates and their details may vary from source to source. [108]
  13. The fact that Julius Caesar fathered only one child, as well as the alleged sterility of his successor, Caesar Augustus, have been attributed to lead poisoning. [140]
  14. The inscription reads: "Made when the Emperor Vespasian was consul for the ninth term and the Emperor Titus was consul for the seventh term, when Gnaeus Iulius Agricola was imperial governor (of Britain)."
  15. Gaseous by-product of the coking process, containing carbon monoxide, hydrogen and methane; used as a fuel.
  16. California began banning lead bullets for hunting on that basis in July 2015. [203]
  17. For example, a firm "...producing quality [lead] garden ornament from our studio in West London for over a century". [210]
  18. Potential injuries to regular users of such batteries are not related to lead's toxicity. [220]
  19. See [222] for details on how a lead–acid battery works.
  20. Rates vary greatly by country. [242]
  21. An alloy of brass (copper and zinc) with lead, iron, tin, and sometimes antimony. [289]

Related Research Articles

Actinium Chemical element with atomic number 89

Actinium is a chemical element with the symbol Ac and atomic number 89. It was first isolated by French chemist André-Louis Debierne in 1899. Friedrich Oskar Giesel later independently isolated it in 1902 and, unaware that it was already known, gave it the name emanium. Actinium gave the name to the actinide series, a group of 15 similar elements between actinium and lawrencium in the periodic table. It is also sometimes considered the first of the 7th-period transition metals, although lawrencium is less commonly given that position. Together with polonium, radium, and radon, actinium was one of the first non-primordial radioactive elements to be isolated.

Astatine Chemical element with atomic number 85

Astatine is a radioactive chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours. A sample of the pure element has never been assembled, because any macroscopic specimen would be immediately vaporized by the heat of its own radioactivity.

Barium Chemical element with atomic number 56

Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Its hydroxide, known in pre-modern times as baryta, does not occur as a mineral, but can be prepared by heating barium carbonate.

Cadmium Chemical element with atomic number 48

Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of its compounds, and like mercury, it has a lower melting point than the transition metals in groups 3 through 11. Cadmium and its congeners in group 12 are often not considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states. The average concentration of cadmium in Earth's crust is between 0.1 and 0.5 parts per million (ppm). It was discovered in 1817 simultaneously by Stromeyer and Hermann, both in Germany, as an impurity in zinc carbonate.

Hassium Chemical element with atomic number 108

Hassium is a chemical element with the symbol Hs and the atomic number 108. It is not known to occur in nature and has been made only in laboratories in minuscule quantities. Hassium is highly radioactive; the most stable known isotope, 269Hs, has a half-life of approximately 16 seconds.

Indium Chemical element with atomic number 49

Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts per million of the Earth's crust. Indium has a melting point higher than sodium and gallium, but lower than lithium and tin. Chemically, indium is similar to gallium and thallium, and it is largely intermediate between the two in terms of its properties. Indium was discovered in 1863 by Ferdinand Reich and Hieronymous Theodor Richter by spectroscopic methods. They named it for the indigo blue line in its spectrum. Indium was isolated the next year.

Lutetium Chemical element with atomic number 71

Lutetium is a chemical element with the symbol Lu and atomic number 71. It is a silvery white metal, which resists corrosion in dry air, but not in moist air. Lutetium is the last element in the lanthanide series, and it is traditionally counted among the rare earths. Lutetium is sometimes considered the first element of the 6th-period transition metals, although lanthanum is more often considered as such.

Osmium Chemical element with atomic number 76

Osmium is a chemical element with the symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, mostly in platinum ores. Osmium is the densest naturally occurring element, with an experimentally measured density of 22.59 g/cm3. Manufacturers use its alloys with platinum, iridium, and other platinum-group metals to make fountain pen nib tipping, electrical contacts, and in other applications that require extreme durability and hardness. The element's abundance in the Earth's crust is among the rarest.

Scandium Chemical element with atomic number 21

Scandium is a chemical element with the symbol Sc and atomic number 21. A silvery-white metallic d-block element, it has historically been classified as a rare-earth element, together with yttrium and the lanthanides. It was discovered in 1879 by spectral analysis of the minerals euxenite and gadolinite from Scandinavia.

Selenium Chemical element with atomic number 34

Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic. It rarely occurs in its elemental state or as pure ore compounds in the Earth's crust. Selenium – from Ancient Greek σελήνη (selḗnē) "Moon" – was discovered in 1817 by Jöns Jacob Berzelius, who noted the similarity of the new element to the previously discovered tellurium.

Tin Chemical element with atomic number 50

Tin is a chemical element with the symbol Sn (from Latin: stannum) and atomic number 50. Tin is a silvery metal that characteristically has a faint yellow hue. Tin, like indium, is soft enough to be cut without much force. When a bar of tin is bent, the so-called tin cry can be heard as a result of sliding tin crystals reforming; this trait is shared by indium, cadmium, and frozen mercury. Pure tin after solidifying keeps a mirror-like appearance similar to most metals. However, in most tin alloys (such as pewter) the metal solidifies with a dull gray color. Tin is a post-transition metal in group 14 of the periodic table of elements. It is obtained chiefly from the mineral cassiterite, which contains stannic oxide, SnO2. Tin shows a chemical similarity to both of its neighbors in group 14, germanium and lead, and has two main oxidation states, +2 and the slightly more stable +4. Tin is the 49th most abundant element on Earth and has, with 10 stable isotopes, the largest number of stable isotopes in the periodic table, thanks to its magic number of protons. It has two main allotropes: at room temperature, the stable allotrope is β-tin, a silvery-white, malleable metal, but at low temperatures, it transforms into the less dense grey α-tin, which has the diamond cubic structure. Metallic tin does not easily oxidize in air.

Thulium Chemical element with atomic number 69

Thulium is a chemical element with the symbol Tm and atomic number 69. It is the thirteenth and third-last element in the lanthanide series. Like the other lanthanides, the most common oxidation state is +3, seen in its oxide, halides and other compounds; because it occurs so late in the series, however, the +2 oxidation state is also stabilized by the nearly full 4f shell that results. In aqueous solution, like compounds of other late lanthanides, soluble thulium compounds form coordination complexes with nine water molecules.

Thallium Chemical element with atomic number 81

Thallium is a chemical element with the symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861, in residues of sulfuric acid production. Both used the newly developed method of flame spectroscopy, in which thallium produces a notable green spectral line. Thallium, from Greek θαλλός, thallós, meaning "a green shoot or twig", was named by Crookes. It was isolated by both Lamy and Crookes in 1862; Lamy by electrolysis, and Crookes by precipitation and melting of the resultant powder. Crookes exhibited it as a powder precipitated by zinc at the International exhibition, which opened on 1 May that year.

Copernicium Chemical element with atomic number 112

Copernicium is a synthetic chemical element with the symbol Cn and atomic number 112. Its known isotopes are extremely radioactive, and have only been created in a laboratory. The most stable known isotope, copernicium-285, has a half-life of approximately 28 seconds. Copernicium was first created in 1996 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany. It is named after the astronomer Nicolaus Copernicus.

Flerovium Chemical element with atomic number 114

Flerovium is a superheavy artificial chemical element with the symbol Fl and atomic number 114. It is an extremely radioactive synthetic element. The element is named after the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in Dubna, Russia, where the element was discovered in 1998. The name of the laboratory, in turn, honours the Russian physicist Georgy Flyorov. The name was adopted by IUPAC on 30 May 2012.

Carbon group group of chemical elements

The carbon group is a periodic table group consisting of carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and flerovium (Fl). It lies within the p-block.

Boron group group of chemical elements

The boron group are the chemical elements in group 13 of the periodic table, comprising boron (B), aluminium (Al), gallium (Ga), indium (In), thallium (Tl), and perhaps also the chemically uncharacterized nihonium (Nh). The elements in the boron group are characterized by having three valence electrons. These elements have also been referred to as the triels.

Bismuth Chemical element with atomic number 83

Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a pentavalent post-transition metal and one of the pnictogens with chemical properties resembling its lighter homologs arsenic and antimony. Elemental bismuth may occur naturally, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead. It is a brittle metal with a silvery white color when freshly produced, but surface oxidation can give it a pink tinge. Bismuth is the most naturally diamagnetic element, and has one of the lowest values of thermal conductivity among metals.

Yttrium Chemical element with atomic number 39

Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals, and is never found in nature as a free element. 89Y is the only stable isotope, and the only isotope found in the Earth's crust.

Cerium Chemical element with atomic number 58

Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile and silvery-white metal that tarnishes when exposed to air, and it is soft enough to be cut with a knife. Cerium is the second element in the lanthanide series, and while it often shows the +3 oxidation state characteristic of the series, it also exceptionally has a stable +4 state that does not oxidize water. It is also considered one of the rare-earth elements. Cerium has no biological role in humans and is not very toxic.

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