Chemical element

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Simple Periodic Table Chart-en.svg
The periodic table of chemical elements with samples of a few elements

A chemical element is a species of atom having the same number of protons in their atomic nuclei (that is, the same atomic number, or Z). [1] For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have exactly 8 protons.

A chemical species is a chemical substance or ensemble composed of chemically identical molecular entities that can explore the same set of molecular energy levels on a characteristic or delineated time scale. The term is applied equally to a set of chemically identical atomic or molecular structural units in a solid array.

Atom smallest unit of a chemical element

An atom is the smallest constituent unit of ordinary matter that has the properties of 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.

Proton nucleon (constituent of the nucleus of the atom) that has positive electric charge; symbol p

A proton is a subatomic particle, symbol
p
or
p+
, with a positive electric charge of +1e elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are collectively referred to as "nucleons".

Contents

118 elements have been identified, of which the first 94 occur naturally on Earth with the remaining 24 being synthetic elements. There are 80 elements that have at least one stable isotope and 38 that have exclusively radionuclides, which decay over time into other elements. Iron is the most abundant element (by mass) making up Earth, while oxygen is the most common element in the Earth's crust. [2]

Earth Third planet from the Sun in the Solar System

Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.

Synthetic element chemical element that does not occur naturally on Earth, and can only be created artificially

In chemistry, a synthetic element is a chemical element that does not occur naturally on Earth, and can only be created artificially. So far, 24 synthetic elements have been created. All are unstable, decaying with half-lives ranging from 15.6 million years to a few hundred microseconds.

Isotope nuclides having the same atomic number but different mass numbers

Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom.

Chemical elements constitute all of the ordinary matter of the universe. However astronomical observations suggest that ordinary observable matter makes up only about 15% of the matter in the universe: the remainder is dark matter; the composition of this is unknown, but it is not composed of chemical elements. [3] The two lightest elements, hydrogen and helium, were mostly formed in the Big Bang and are the most common elements in the universe. The next three elements (lithium, beryllium and boron) were formed mostly by cosmic ray spallation, and are thus rarer than heavier elements. Formation of elements with from 6 to 26 protons occurred and continues to occur in main sequence stars via stellar nucleosynthesis. The high abundance of oxygen, silicon, and iron on Earth reflects their common production in such stars. Elements with greater than 26 protons are formed by supernova nucleosynthesis in supernovae, which, when they explode, blast these elements as supernova remnants far into space, where they may become incorporated into planets when they are formed. [4]

Matter substance that has rest mass and volume, or several other definitions

In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic particles, and in everyday as well as scientific usage, "matter" generally includes atoms and anything made up of them, and any particles that act as if they have both rest mass and volume. However it does not include massless particles such as photons, or other energy phenomena or waves such as light or sound. Matter exists in various states. These include classical everyday phases such as solid, liquid, and gas – for example water exists as ice, liquid water, and gaseous steam – but other states are possible, including plasma, Bose–Einstein condensates, fermionic condensates, and quark–gluon plasma.

Observational astronomy part of astronomical science concerned with recording data

Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical models. It is the practice and study of observing celestial objects with the use of telescopes and other astronomical instruments.

Dark matter Hypothetical form of matter comprising most of the matter in the universe

Dark matter is a hypothetical form of matter that is thought to account for approximately 85% of the matter in the universe, and about a quarter of its total energy density. The majority of dark matter is thought to be non-baryonic in nature, possibly being composed of some as-yet undiscovered subatomic particles. Its presence is implied in a variety of astrophysical observations, including gravitational effects that cannot be explained unless more matter is present than can be seen. For this reason, most experts think dark matter to be ubiquitous in the universe and to have had a strong influence on its structure and evolution. Dark matter is called dark because it does not appear to interact with observable electromagnetic radiation, such as light, and is thus invisible to the entire electromagnetic spectrum, making it extremely difficult to detect using usual astronomical equipment.

The term "element" is used for atoms with a given number of protons (regardless of whether or not they are ionized or chemically bonded, e.g. hydrogen in water) as well as for a pure chemical substance consisting of a single element (e.g. hydrogen gas). [1] For the second meaning, the terms "elementary substance" and "simple substance" have been suggested, but they have not gained much acceptance in English chemical literature, whereas in some other languages their equivalent is widely used (e.g. French corps simple, Russian простое вещество). A single element can form multiple substances differing in their structure; they are called allotropes of the element.

Ionization or ionisation, is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion. Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules and ions, or through the interaction with electromagnetic radiation. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected.

Water chemical compound

Water is a transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's streams, lakes, and oceans, and the fluids of most living organisms. It is vital for all known forms of life, even though it provides no calories or organic nutrients. Its chemical formula is H2O, meaning that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. Water is the name of the liquid state of H2O at standard ambient temperature and pressure. It forms precipitation in the form of rain and aerosols in the form of fog. Clouds are formed from suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor. Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.

Chemical substance matter of constant composition best characterized by the entities (molecules, formula units, atoms) it is composed of

A chemical substance is a form of matter having constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be simple substances, chemical compounds, or alloys. Chemical elements may or may not be included in the definition, depending on expert viewpoint.

When different elements are chemically combined, with the atoms held together by chemical bonds, they form chemical compounds. Only a minority of elements are found uncombined as relatively pure minerals. Among the more common of such native elements are copper, silver, gold, carbon (as coal, graphite, or diamonds), and sulfur. All but a few of the most inert elements, such as noble gases and noble metals, are usually found on Earth in chemically combined form, as chemical compounds. While about 32 of the chemical elements occur on Earth in native uncombined forms, most of these occur as mixtures. For example, atmospheric air is primarily a mixture of nitrogen, oxygen, and argon, and native solid elements occur in alloys, such as that of iron and nickel.

Chemical bond lasting attraction between atoms that enables the formation of chemical compounds

A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may result from the electrostatic force of attraction between oppositely charged ions as in ionic bonds or through the sharing of electrons as in covalent bonds. The strength of chemical bonds varies considerably; there are "strong bonds" or "primary bonds" such as covalent, ionic and metallic bonds, and "weak bonds" or "secondary bonds" such as dipole–dipole interactions, the London dispersion force and hydrogen bonding.

Chemical compound Substance composed of multiple elements

A chemical compound is a chemical substance composed of many identical molecules composed of atoms from more than one element held together by chemical bonds. A chemical element bonded to an identical chemical element is not a chemical compound since only one element, not two different elements, is involved.

Mineral Element or chemical compound that is normally crystalline and that has been formed as a result of geological processes

A mineral is, broadly speaking, a solid chemical compound that occurs naturally in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are usually excluded, but some minerals are often biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings often syntesize inorganic minerals that also occur in rocks.

The history of the discovery and use of the elements began with primitive human societies that found native elements like carbon, sulfur, copper and gold. Later civilizations extracted elemental copper, tin, lead and iron from their ores by smelting, using charcoal. Alchemists and chemists subsequently identified many more; all of the naturally occurring elements were known by 1950.

In phylogenetics, a primitive character, trait, or feature of a lineage or taxon is one that is inherited from the common ancestor of a clade and has undergone little change since. Conversely, a trait that appears within the clade group is called advanced or derived. A clade is a group of organisms that consists of a common ancestor and all its lineal descendants.

Society group of people related to each other through persistent relations, or a large social grouping sharing the same territory, subject to the same authority and culture

A society is a group of individuals involved in persistent social interaction, or a large social group sharing the same geographical or social territory, typically subject to the same political authority and dominant cultural expectations. Societies are characterized by patterns of relationships between individuals who share a distinctive culture and institutions; a given society may be described as the sum total of such relationships among its constituent of members. In the social sciences, a larger society often exhibits stratification or dominance patterns in subgroups.

Ore rock with valuable metals, minerals and elements

An ore is an 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 from the earth through mining; they are then refined to extract the valuable element, or elements.

The properties of the chemical elements are summarized in the periodic table, which organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. Save for unstable radioactive elements with short half-lives, all of the elements are available industrially, most of them in low degrees of impurities.

Description

The lightest chemical elements are hydrogen and helium, both created by Big Bang nucleosynthesis during the first 20 minutes of the universe [5] in a ratio of around 3:1 by mass (or 12:1 by number of atoms), [6] [7] along with tiny traces of the next two elements, lithium and beryllium. Almost all other elements found in nature were made by various natural methods of nucleosynthesis. [8] On Earth, small amounts of new atoms are naturally produced in nucleogenic reactions, or in cosmogenic processes, such as cosmic ray spallation. New atoms are also naturally produced on Earth as radiogenic daughter isotopes of ongoing radioactive decay processes such as alpha decay, beta decay, spontaneous fission, cluster decay, and other rarer modes of decay.

Of the 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope (except for technetium, element 43 and promethium, element 61, which have no stable isotopes). Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected. Some of these elements, notably bismuth (atomic number 83), thorium (atomic number 90), and uranium (atomic number 92), have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy metals before the formation of our Solar System. At over 1.9×1019 years, over a billion times longer than the current estimated age of the universe, bismuth-209 (atomic number 83) has the longest known alpha decay half-life of any naturally occurring element, and is almost always considered on par with the 80 stable elements. [9] [10] The very heaviest elements (those beyond plutonium, element 94) undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized.

As of 2010, there are 118 known elements (in this context, "known" means observed well enough, even from just a few decay products, to have been differentiated from other elements). [11] [12] Of these 118 elements, 94 occur naturally on Earth. Six of these occur in extreme trace quantities: technetium, atomic number 43; promethium, number 61; astatine, number 85; francium, number 87; neptunium, number 93; and plutonium, number 94. These 94 elements have been detected in the universe at large, in the spectra of stars and also supernovae, where short-lived radioactive elements are newly being made. The first 94 elements have been detected directly on Earth as primordial nuclides present from the formation of the solar system, or as naturally occurring fission or transmutation products of uranium and thorium.

The remaining 24 heavier elements, not found today either on Earth or in astronomical spectra, have been produced artificially: these are all radioactive, with very short half-lives; if any atoms of these elements were present at the formation of Earth, they are extremely likely, to the point of certainty, to have already decayed, and if present in novae have been in quantities too small to have been noted. Technetium was the first purportedly non-naturally occurring element synthesized, in 1937, although trace amounts of technetium have since been found in nature (and also the element may have been discovered naturally in 1925). [13] This pattern of artificial production and later natural discovery has been repeated with several other radioactive naturally occurring rare elements. [14]

List of the elements are available by name, atomic number, density, melting point, boiling point and by symbol, as well as ionization energies of the elements. The nuclides of stable and radioactive elements are also available as a list of nuclides, sorted by length of half-life for those that are unstable. One of the most convenient, and certainly the most traditional presentation of the elements, is in the form of the periodic table, which groups together elements with similar chemical properties (and usually also similar electronic structures).

Atomic number

The atomic number of an element is equal to the number of protons in each atom, and defines the element. [15] For example, all carbon atoms contain 6 protons in their atomic nucleus; so the atomic number of carbon is 6. [16] Carbon atoms may have different numbers of neutrons; atoms of the same element having different numbers of neutrons are known as isotopes of the element. [17]

The number of protons in the atomic nucleus also determines its electric charge, which in turn determines the number of electrons of the atom in its non-ionized state. The electrons are placed into atomic orbitals that determine the atom's various chemical properties. The number of neutrons in a nucleus usually has very little effect on an element's chemical properties (except in the case of hydrogen and deuterium). Thus, all carbon isotopes have nearly identical chemical properties because they all have six protons and six electrons, even though carbon atoms may, for example, have 6 or 8 neutrons. That is why the atomic number, rather than mass number or atomic weight, is considered the identifying characteristic of a chemical element.

The symbol for atomic number is Z.

Isotopes

Isotopes are atoms of the same element (that is, with the same number of protons in their atomic nucleus), but having different numbers of neutrons. Thus, for example, there are three main isotopes of carbon. All carbon atoms have 6 protons in the nucleus, but they can have either 6, 7, or 8 neutrons. Since the mass numbers of these are 12, 13 and 14 respectively, the three isotopes of carbon are known as carbon-12, carbon-13, and carbon-14, often abbreviated to 12C, 13C, and 14C. Carbon in everyday life and in chemistry is a mixture of 12C (about 98.9%), 13C (about 1.1%) and about 1 atom per trillion of 14C.

Most (66 of 94) naturally occurring elements have more than one stable isotope. Except for the isotopes of hydrogen (which differ greatly from each other in relative mass—enough to cause chemical effects), the isotopes of a given element are chemically nearly indistinguishable.

All of the elements have some isotopes that are radioactive (radioisotopes), although not all of these radioisotopes occur naturally. The radioisotopes typically decay into other elements upon radiating an alpha or beta particle. If an element has isotopes that are not radioactive, these are termed "stable" isotopes. All of the known stable isotopes occur naturally (see primordial isotope). The many radioisotopes that are not found in nature have been characterized after being artificially made. Certain elements have no stable isotopes and are composed only of radioactive isotopes: specifically the elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic numbers greater than 82.

Of the 80 elements with at least one stable isotope, 26 have only one single stable isotope. The mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes that occur for a single element is 10 (for tin, element 50).

Isotopic mass and atomic mass

The mass number of an element, A, is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes of a given element are distinguished by their mass numbers, which are conventionally written as a superscript on the left hand side of the atomic symbol (e.g. 238U). The mass number is always a whole number and has units of "nucleons". For example, magnesium-24 (24 is the mass number) is an atom with 24 nucleons (12 protons and 12 neutrons).

Whereas the mass number simply counts the total number of neutrons and protons and is thus a natural (or whole) number, the atomic mass of a single atom is a real number giving the mass of a particular isotope (or "nuclide") of the element, expressed in atomic mass units (symbol: u). In general, the mass number of a given nuclide differs in value slightly from its atomic mass, since the mass of each proton and neutron is not exactly 1 u; since the electrons contribute a lesser share to the atomic mass as neutron number exceeds proton number; and (finally) because of the nuclear binding energy. For example, the atomic mass of chlorine-35 to five significant digits is 34.969 u and that of chlorine-37 is 36.966 u. However, the atomic mass in u of each isotope is quite close to its simple mass number (always within 1%). The only isotope whose atomic mass is exactly a natural number is 12C, which by definition has a mass of exactly 12 because u is defined as 1/12 of the mass of a free neutral carbon-12 atom in the ground state.

The standard atomic weight (commonly called "atomic weight") of an element is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance, relative to the atomic mass unit. This number may be a fraction that is not close to a whole number. For example, the relative atomic mass of chlorine is 35.453 u, which differs greatly from a whole number as it is an average of about 76% chlorine-35 and 24% chlorine-37. Whenever a relative atomic mass value differs by more than 1% from a whole number, it is due to this averaging effect, as significant amounts of more than one isotope are naturally present in a sample of that element.

Chemically pure and isotopically pure

Chemists and nuclear scientists have different definitions of a pure element. In chemistry, a pure element means a substance whose atoms all (or in practice almost all) have the same atomic number, or number of protons. Nuclear scientists, however, define a pure element as one that consists of only one stable isotope. [18]

For example, a copper wire is 99.99% chemically pure if 99.99% of its atoms are copper, with 29 protons each. However it is not isotopically pure since ordinary copper consists of two stable isotopes, 69% 63Cu and 31% 65Cu, with different numbers of neutrons. However, a pure gold ingot would be both chemically and isotopically pure, since ordinary gold consists only of one isotope, 197Au.

Allotropes

Atoms of chemically pure elements may bond to each other chemically in more than one way, allowing the pure element to exist in multiple chemical structures (spatial arrangements of atoms), known as allotropes, which differ in their properties. For example, carbon can be found as diamond, which has a tetrahedral structure around each carbon atom; graphite, which has layers of carbon atoms with a hexagonal structure stacked on top of each other; graphene, which is a single layer of graphite that is very strong; fullerenes, which have nearly spherical shapes; and carbon nanotubes, which are tubes with a hexagonal structure (even these may differ from each other in electrical properties). The ability of an element to exist in one of many structural forms is known as 'allotropy'.

The standard state, also known as the reference state, of an element is defined as its thermodynamically most stable state at a pressure of 1 bar and a given temperature (typically at 298.15 K). In thermochemistry, an element is defined to have an enthalpy of formation of zero in its standard state. For example, the reference state for carbon is graphite, because the structure of graphite is more stable than that of the other allotropes.

Properties

Several kinds of descriptive categorizations can be applied broadly to the elements, including consideration of their general physical and chemical properties, their states of matter under familiar conditions, their melting and boiling points, their densities, their crystal structures as solids, and their origins.

General properties

Several terms are commonly used to characterize the general physical and chemical properties of the chemical elements. A first distinction is between metals, which readily conduct electricity, nonmetals, which do not, and a small group, (the metalloids ), having intermediate properties and often behaving as semiconductors.

A more refined classification is often shown in colored presentations of the periodic table. This system restricts the terms "metal" and "nonmetal" to only certain of the more broadly defined metals and nonmetals, adding additional terms for certain sets of the more broadly viewed metals and nonmetals. The version of this classification used in the periodic tables presented here includes: actinides, alkali metals, alkaline earth metals, halogens, lanthanides, transition metals, post-transition metals, metalloids, reactive nonmetals, and noble gases. In this system, the alkali metals, alkaline earth metals, and transition metals, as well as the lanthanides and the actinides, are special groups of the metals viewed in a broader sense. Similarly, the reactive nonmetals and the noble gases are nonmetals viewed in the broader sense. In some presentations, the halogens are not distinguished, with astatine identified as a metalloid and the others identified as nonmetals.

States of matter

Another commonly used basic distinction among the elements is their state of matter (phase), whether solid, liquid, or gas, at a selected standard temperature and pressure (STP). Most of the elements are solids at conventional temperatures and atmospheric pressure, while several are gases. Only bromine and mercury are liquids at 0 degrees Celsius (32 degrees Fahrenheit) and normal atmospheric pressure; caesium and gallium are solids at that temperature, but melt at 28.4 °C (83.2 °F) and 29.8 °C (85.6 °F), respectively.

Melting and boiling points

Melting and boiling points, typically expressed in degrees Celsius at a pressure of one atmosphere, are commonly used in characterizing the various elements. While known for most elements, either or both of these measurements is still undetermined for some of the radioactive elements available in only tiny quantities. Since helium remains a liquid even at absolute zero at atmospheric pressure, it has only a boiling point, and not a melting point, in conventional presentations.

Densities

The density at selected standard temperature and pressure (STP) is frequently used in characterizing the elements. Density is often expressed in grams per cubic centimeter (g/cm3). Since several elements are gases at commonly encountered temperatures, their densities are usually stated for their gaseous forms; when liquefied or solidified, the gaseous elements have densities similar to those of the other elements.

When an element has allotropes with different densities, one representative allotrope is typically selected in summary presentations, while densities for each allotrope can be stated where more detail is provided. For example, the three familiar allotropes of carbon (amorphous carbon, graphite, and diamond) have densities of 1.8–2.1, 2.267, and 3.515 g/cm3, respectively.

Crystal structures

The elements studied to date as solid samples have eight kinds of crystal structures: cubic, body-centered cubic, face-centered cubic, hexagonal, monoclinic, orthorhombic, rhombohedral, and tetragonal. For some of the synthetically produced transuranic elements, available samples have been too small to determine crystal structures.

Occurrence and origin on Earth

Chemical elements may also be categorized by their origin on Earth, with the first 94 considered naturally occurring, while those with atomic numbers beyond 94 have only been produced artificially as the synthetic products of man-made nuclear reactions.

Of the 94 naturally occurring elements, 83 are considered primordial and either stable or weakly radioactive. The remaining 11 naturally occurring elements possess half lives too short for them to have been present at the beginning of the Solar System, and are therefore considered transient elements. Of these 11 transient elements, 5 (polonium, radon, radium, actinium, and protactinium) are relatively common decay products of thorium and uranium. The remaining 6 transient elements (technetium, promethium, astatine, francium, neptunium, and plutonium) occur only rarely, as products of rare decay modes or nuclear reaction processes involving uranium or other heavy elements.

No radioactive decay has been observed for elements with atomic numbers 1 through 82, except 43 (technetium) and 61 (promethium). Observationally stable isotopes of some elements (such as tungsten and lead), however, are predicted to be slightly radioactive with very long half-lives. [19] Elements with atomic numbers 43, 61, and 83 through 94 are unstable enough that their radioactive decay can readily be detected. Three of these elements, bismuth (element 83), thorium (element 90), and uranium (element 92) have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy elements before the formation of our solar system. For example, at over 1.9×1019 years, over a billion times longer than the current estimated age of the universe, bismuth-209 has the longest known alpha decay half-life of any naturally occurring element. [9] [10] The very heaviest 24 elements (those beyond plutonium, element 94) undergo radioactive decay with short half-lives and cannot be produced as daughters of longer-lived elements, and thus they do not occur in nature at all.

Periodic table

Periodic table
Group 1 2 3   4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Alkali metalsAlkaline earth metalsPnicto­gensChal­co­gensHalo­gensNoble gases
Period

1

Hydro­gen1H1.008 He­lium2He4.0026
2 Lith­ium3Li6.94 Beryl­lium4Be9.0122 Boron5B10.81 Carbon6C12.011 Nitro­gen7N14.007 Oxy­gen8O15.999 Fluor­ine9F18.998 Neon10Ne20.180
3 So­dium11Na22.990 Magne­sium12Mg24.305 Alumin­ium13Al26.982 Sili­con14Si28.085 Phos­phorus15P30.974 Sulfur16S32.06 Chlor­ine17Cl35.45 Argon18Ar39.948
4 Potas­sium19K39.098 Cal­cium20Ca40.078 Scan­dium21Sc44.956 Tita­nium22Ti47.867 Vana­dium23V50.942 Chrom­ium24Cr51.996 Manga­nese25Mn54.938 Iron26Fe55.845 Cobalt27Co58.933 Nickel28Ni58.693 Copper29Cu63.546 Zinc30Zn65.38 Gallium31Ga69.723 Germa­nium32Ge72.630 Arsenic33As74.922 Sele­nium34Se78.971 Bromine35Br79.904 Kryp­ton36Kr83.798
5 Rubid­ium37Rb85.468 Stront­ium38Sr87.62 Yttrium39Y88.906 Zirco­nium40Zr91.224 Nio­bium41Nb92.906 Molyb­denum42Mo95.95 Tech­netium43Tc[98] Ruthe­nium44Ru101.07 Rho­dium45Rh102.91 Pallad­ium46Pd106.42 Silver47Ag107.87 Cad­mium48Cd112.41 Indium49In114.82 Tin50Sn118.71 Anti­mony51Sb121.76 Tellur­ium52Te127.60 Iodine53I126.90 Xenon54Xe131.29
6 Cae­sium55Cs132.91 Ba­rium56Ba137.33 Lan­thanum57La138.91 Asterisks one.svg Haf­nium72Hf178.49 Tanta­lum73Ta180.95 Tung­sten74W183.84 Rhe­nium75Re186.21 Os­mium76Os190.23 Iridium77Ir192.22 Plat­inum78Pt195.08 Gold79Au196.97 Mer­cury80Hg200.59 Thallium81Tl204.38 Lead82Pb207.2 Bis­muth83Bi208.98 Polo­nium84Po[209] Asta­tine85At[210] Radon86Rn[222]
7 Fran­cium87Fr[223] Ra­dium88Ra[226] Actin­ium89Ac[227] Asterisks 2 (vertical).svg Ruther­fordium104Rf[267] Dub­nium105Db[268] Sea­borgium106Sg[269] Bohr­ium107Bh[270] Has­sium108Hs[270] Meit­nerium109Mt[278] Darm­stadtium110Ds[281] Roent­genium111Rg[282] Coper­nicium112Cn[285] Nihon­ium113Nh[286] Flerov­ium114Fl[289] Moscov­ium115Mc[290] Liver­morium116Lv[293] Tenness­ine117Ts[294] Oga­nesson118Og[294]
Asterisks one.svg Cerium58Ce140.12 Praseo­dymium59Pr140.91 Neo­dymium60Nd144.24 Prome­thium61Pm[145] Sama­rium62Sm150.36 Europ­ium63Eu151.96 Gadolin­ium64Gd157.25 Ter­bium65Tb158.93 Dyspro­sium66Dy162.50 Hol­mium67Ho164.93 Erbium68Er167.26 Thulium69Tm168.93 Ytter­bium70Yb173.05 Lute­tium71Lu174.97  
Asterisks 2 (vertical).svg Thor­ium90Th232.04 Protac­tinium91Pa231.04 Ura­nium92U238.03 Neptu­nium93Np[237] Pluto­nium94Pu[244] Ameri­cium95Am[243] Curium96Cm[247] Berkel­ium97Bk[247] Califor­nium98Cf[251] Einstei­nium99Es[252] Fer­mium100Fm[257] Mende­levium101Md[258] Nobel­ium102No[259] Lawren­cium103Lr[266]

The properties of the chemical elements are often summarized using the periodic table, which powerfully and elegantly organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. The current standard table contains 118 confirmed elements as of 10 April 2010.

Although earlier precursors to this presentation exist, its invention is generally credited to the Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring trends in the properties of the elements. The layout of the table has been refined and extended over time as new elements have been discovered and new theoretical models have been developed to explain chemical behavior.

Use of the periodic table is now ubiquitous within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize and compare all the many different forms of chemical behavior. The table has also found wide application in physics, geology, biology, materials science, engineering, agriculture, medicine, nutrition, environmental health, and astronomy. Its principles are especially important in chemical engineering.

Nomenclature and symbols

The various chemical elements are formally identified by their unique atomic numbers, by their accepted names, and by their symbols.

Atomic numbers

The known elements have atomic numbers from 1 through 118, conventionally presented as Arabic numerals. Since the elements can be uniquely sequenced by atomic number, conventionally from lowest to highest (as in a periodic table), sets of elements are sometimes specified by such notation as "through", "beyond", or "from ... through", as in "through iron", "beyond uranium", or "from lanthanum through lutetium". The terms "light" and "heavy" are sometimes also used informally to indicate relative atomic numbers (not densities), as in "lighter than carbon" or "heavier than lead", although technically the weight or mass of atoms of an element (their atomic weights or atomic masses) do not always increase monotonically with their atomic numbers.

Element names

The naming of various substances now known as elements precedes the atomic theory of matter, as names were given locally by various cultures to various minerals, metals, compounds, alloys, mixtures, and other materials, although at the time it was not known which chemicals were elements and which compounds. As they were identified as elements, the existing names for anciently-known elements (e.g., gold, mercury, iron) were kept in most countries. National differences emerged over the names of elements either for convenience, linguistic niceties, or nationalism. For a few illustrative examples: German speakers use "Wasserstoff" (water substance) for "hydrogen", "Sauerstoff" (acid substance) for "oxygen" and "Stickstoff" (smothering substance) for "nitrogen", while English and some romance languages use "sodium" for "natrium" and "potassium" for "kalium", and the French, Italians, Greeks, Portuguese and Poles prefer "azote/azot/azoto" (from roots meaning "no life") for "nitrogen".

For purposes of international communication and trade, the official names of the chemical elements both ancient and more recently recognized are decided by the International Union of Pure and Applied Chemistry (IUPAC), which has decided on a sort of international English language, drawing on traditional English names even when an element's chemical symbol is based on a Latin or other traditional word, for example adopting "gold" rather than "aurum" as the name for the 79th element (Au). IUPAC prefers the British spellings "aluminium" and "caesium" over the U.S. spellings "aluminum" and "cesium", and the U.S. "sulfur" over the British "sulphur". However, elements that are practical to sell in bulk in many countries often still have locally used national names, and countries whose national language does not use the Latin alphabet are likely to use the IUPAC element names.

According to IUPAC, chemical elements are not proper nouns in English; consequently, the full name of an element is not routinely capitalized in English, even if derived from a proper noun, as in californium and einsteinium. Isotope names of chemical elements are also uncapitalized if written out, e.g., carbon-12 or uranium-235. Chemical element symbols (such as Cf for californium and Es for einsteinium), are always capitalized (see below).

In the second half of the twentieth century, physics laboratories became able to produce nuclei of chemical elements with half-lives too short for an appreciable amount of them to exist at any time. These are also named by IUPAC, which generally adopts the name chosen by the discoverer. This practice can lead to the controversial question of which research group actually discovered an element, a question that delayed the naming of elements with atomic number of 104 and higher for a considerable amount of time. (See element naming controversy).

Precursors of such controversies involved the nationalistic namings of elements in the late 19th century. For example, lutetium was named in reference to Paris, France. The Germans were reluctant to relinquish naming rights to the French, often calling it cassiopeium. Similarly, the British discoverer of niobium originally named it columbium, in reference to the New World. It was used extensively as such by American publications before the international standardization (in 1950).

Chemical symbols

Specific chemical elements

Before chemistry became a science, alchemists had designed arcane symbols for both metals and common compounds. These were however used as abbreviations in diagrams or procedures; there was no concept of atoms combining to form molecules. With his advances in the atomic theory of matter, John Dalton devised his own simpler symbols, based on circles, to depict molecules.

The current system of chemical notation was invented by Berzelius. In this typographical system, chemical symbols are not mere abbreviations—though each consists of letters of the Latin alphabet. They are intended as universal symbols for people of all languages and alphabets.

The first of these symbols were intended to be fully universal. Since Latin was the common language of science at that time, they were abbreviations based on the Latin names of metals. Cu comes from cuprum, Fe comes from ferrum, Ag from argentum. The symbols were not followed by a period (full stop) as with abbreviations. Later chemical elements were also assigned unique chemical symbols, based on the name of the element, but not necessarily in English. For example, sodium has the chemical symbol 'Na' after the Latin natrium. The same applies to "W" (wolfram) for tungsten, "Fe" (ferrum) for iron, "Hg" (hydrargyrum) for mercury, "Sn" (stannum) for tin, "K" (kalium) for potassium, "Au" (aurum) for gold, "Ag" (argentum) for silver, "Pb" (plumbum) for lead, "Cu" (cuprum) for copper, and "Sb" (stibium) for antimony.

Chemical symbols are understood internationally when element names might require translation. There have sometimes been differences in the past. For example, Germans in the past have used "J" (for the alternate name Jod) for iodine, but now use "I" and "Iod".

The first letter of a chemical symbol is always capitalized, as in the preceding examples, and the subsequent letters, if any, are always lower case (small letters). Thus, the symbols for californium and einsteinium are Cf and Es.

General chemical symbols

There are also symbols in chemical equations for groups of chemical elements, for example in comparative formulas. These are often a single capital letter, and the letters are reserved and not used for names of specific elements. For example, an "X" indicates a variable group (usually a halogen) in a class of compounds, while "R" is a radical, meaning a compound structure such as a hydrocarbon chain. The letter "Q" is reserved for "heat" in a chemical reaction. "Y" is also often used as a general chemical symbol, although it is also the symbol of yttrium. "Z" is also frequently used as a general variable group. "E" is used in organic chemistry to denote an electron-withdrawing group or an electrophile; similarly "Nu" denotes a nucleophile. "L" is used to represent a general ligand in inorganic and organometallic chemistry. "M" is also often used in place of a general metal.

At least two additional, two-letter generic chemical symbols are also in informal usage, "Ln" for any lanthanide element and "An" for any actinide element. "Rg" was formerly used for any rare gas element, but the group of rare gases has now been renamed noble gases and the symbol "Rg" has now been assigned to the element roentgenium.

Isotope symbols

Isotopes are distinguished by the atomic mass number (total protons and neutrons) for a particular isotope of an element, with this number combined with the pertinent element's symbol. IUPAC prefers that isotope symbols be written in superscript notation when practical, for example 12C and 235U. However, other notations, such as carbon-12 and uranium-235, or C-12 and U-235, are also used.

As a special case, the three naturally occurring isotopes of the element hydrogen are often specified as H for 1H (protium), D for 2H (deuterium), and T for 3H (tritium). This convention is easier to use in chemical equations, replacing the need to write out the mass number for each atom. For example, the formula for heavy water may be written D2O instead of 2H2O.

Origin of the elements

Estimated distribution of dark matter and dark energy in the universe. Only the fraction of the mass and energy in the universe labeled "atoms" is composed of chemical elements. Universe content pie chart.jpg
Estimated distribution of dark matter and dark energy in the universe. Only the fraction of the mass and energy in the universe labeled "atoms" is composed of chemical elements.

Only about 4% of the total mass of the universe is made of atoms or ions, and thus represented by chemical elements. This fraction is about 15% of the total matter, with the remainder of the matter (85%) being dark matter. The nature of dark matter is unknown, but it is not composed of atoms of chemical elements because it contains no protons, neutrons, or electrons. (The remaining non-matter part of the mass of the universe is composed of the even more mysterious dark energy).

The universe's 94 naturally occurring chemical elements are thought to have been produced by at least four cosmic processes. Most of the hydrogen, helium and a very small quantity of lithiumin the universe was produced primordially in the first few minutes of the Big Bang. Other three recurrently occurring later processes are thought to have produced the remaining elements. Stellar nucleosynthesis, an ongoing process inside stars, produces all elements from carbon through iron in atomic number, but little lithium, beryllium, or boron. Elements heavier in atomic number than iron, as heavy as uranium and plutonium, are produced by explosive nucleosynthesis in supernovas and other cataclysmic cosmic events. Cosmic ray spallation (fragmentation) of carbon, nitrogen, and oxygen is important to the production of lithium, beryllium and boron.

During the early phases of the Big Bang, nucleosynthesis of hydrogen nuclei resulted in the production of hydrogen-1 (protium, 1H) and helium-4 (4He), as well as a smaller amount of deuterium (2H) and very minuscule amounts (on the order of 10−10) of lithium and beryllium. Even smaller amounts of boron may have been produced in the Big Bang, since it has been observed in some very old stars, while carbon has not. [22] It is generally agreed that no heavier elements than boron were produced in the Big Bang. As a result, the primordial abundance of atoms (or ions) consisted of roughly 75% 1H, 25% 4He, and 0.01% deuterium, with only tiny traces of lithium, beryllium, and perhaps boron. [23] Subsequent enrichment of galactic halos occurred due to stellar nucleosynthesis and supernova nucleosynthesis. [24] However, the element abundance in intergalactic space can still closely resemble primordial conditions, unless it has been enriched by some means.

Periodic table showing the cosmogenic origin of each element in the Big Bang, or in large or small stars. Small stars can produce certain elements up to sulfur, by the alpha process. Supernovae are needed to produce "heavy" elements (those beyond iron and nickel) rapidly by neutron buildup, in the r-process. Certain large stars slowly produce other elements heavier than iron, in the s-process; these may then be blown into space in the off-gassing of planetary nebulae Nucleosynthesis periodic table.svg
Periodic table showing the cosmogenic origin of each element in the Big Bang, or in large or small stars. Small stars can produce certain elements up to sulfur, by the alpha process. Supernovae are needed to produce "heavy" elements (those beyond iron and nickel) rapidly by neutron buildup, in the r-process. Certain large stars slowly produce other elements heavier than iron, in the s-process; these may then be blown into space in the off-gassing of planetary nebulae

On Earth (and elsewhere), trace amounts of various elements continue to be produced from other elements as products of nuclear transmutation processes. These include some produced by cosmic rays or other nuclear reactions (see cosmogenic and nucleogenic nuclides), and others produced as decay products of long-lived primordial nuclides. [25] For example, trace (but detectable) amounts of carbon-14 (14C) are continually produced in the atmosphere by cosmic rays impacting nitrogen atoms, and argon-40 (40Ar) is continually produced by the decay of primordially occurring but unstable potassium-40 (40K). Also, three primordially occurring but radioactive actinides, thorium, uranium, and plutonium, decay through a series of recurrently produced but unstable radioactive elements such as radium and radon, which are transiently present in any sample of these metals or their ores or compounds. Three other radioactive elements, technetium, promethium, and neptunium, occur only incidentally in natural materials, produced as individual atoms by nuclear fission of the nuclei of various heavy elements or in other rare nuclear processes.

Human technology has produced various additional elements beyond these first 94, with those through atomic number 118 now known.

Abundance

The following graph (note log scale) shows the abundance of elements in our Solar System. The table shows the twelve most common elements in our galaxy (estimated spectroscopically), as measured in parts per million, by mass. [26] Nearby galaxies that have evolved along similar lines have a corresponding enrichment of elements heavier than hydrogen and helium. The more distant galaxies are being viewed as they appeared in the past, so their abundances of elements appear closer to the primordial mixture. As physical laws and processes appear common throughout the visible universe, however, scientist expect that these galaxies evolved elements in similar abundance.

The abundance of elements in the Solar System is in keeping with their origin from nucleosynthesis in the Big Bang and a number of progenitor supernova stars. Very abundant hydrogen and helium are products of the Big Bang, but the next three elements are rare since they had little time to form in the Big Bang and are not made in stars (they are, however, produced in small quantities by the breakup of heavier elements in interstellar dust, as a result of impact by cosmic rays). Beginning with carbon, elements are produced in stars by buildup from alpha particles (helium nuclei), resulting in an alternatingly larger abundance of elements with even atomic numbers (these are also more stable). In general, such elements up to iron are made in large stars in the process of becoming supernovas. Iron-56 is particularly common, since it is the most stable element that can easily be made from alpha particles (being a product of decay of radioactive nickel-56, ultimately made from 14 helium nuclei). Elements heavier than iron are made in energy-absorbing processes in large stars, and their abundance in the universe (and on Earth) generally decreases with their atomic number.

The abundance of the chemical elements on Earth varies from air to crust to ocean, and in various types of life. The abundance of elements in Earth's crust differs from that in the Solar system (as seen in the Sun and heavy planets like Jupiter) mainly in selective loss of the very lightest elements (hydrogen and helium) and also volatile neon, carbon (as hydrocarbons), nitrogen and sulfur, as a result of solar heating in the early formation of the solar system. Oxygen, the most abundant Earth element by mass, is retained on Earth by combination with silicon. Aluminum at 8% by mass is more common in the Earth's crust than in the universe and solar system, but the composition of the far more bulky mantle, which has magnesium and iron in place of aluminum (which occurs there only at 2% of mass) more closely mirrors the elemental composition of the solar system, save for the noted loss of volatile elements to space, and loss of iron which has migrated to the Earth's core.

The composition of the human body, by contrast, more closely follows the composition of seawater—save that the human body has additional stores of carbon and nitrogen necessary to form the proteins and nucleic acids, together with phosphorus in the nucleic acids and energy transfer molecule adenosine triphosphate (ATP) that occurs in the cells of all living organisms. Certain kinds of organisms require particular additional elements, for example the magnesium in chlorophyll in green plants, the calcium in mollusc shells, or the iron in the hemoglobin in vertebrate animals' red blood cells.

Abundances of the chemical elements in the Solar system. Hydrogen and helium are most common, from the Big Bang. The next three elements (Li, Be, B) are rare because they are poorly synthesized in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance in elements as they have even or odd atomic numbers (the Oddo-Harkins rule), and (2) a general decrease in abundance as elements become heavier. Iron is especially common because it represents the minimum energy nuclide that can be made by fusion of helium in supernovae. SolarSystemAbundances.png
Abundances of the chemical elements in the Solar system. Hydrogen and helium are most common, from the Big Bang. The next three elements (Li, Be, B) are rare because they are poorly synthesized in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance in elements as they have even or odd atomic numbers (the Oddo-Harkins rule), and (2) a general decrease in abundance as elements become heavier. Iron is especially common because it represents the minimum energy nuclide that can be made by fusion of helium in supernovae.
Elements in our galaxyParts per million
by mass
Hydrogen 739,000
Helium 240,000
Oxygen 10,400
Carbon 4,600
Neon 1,340
Iron 1,090
Nitrogen 960
Silicon 650
Magnesium 580
Sulfur 440
Potassium 210
Nickel 100
Nutritional elements in the periodic table
H He
LiBe BCNOFNe
NaMg AlSiPSClAr
KCaSc TiVCrMnFeCoNiCuZnGaGeAsSeBrKr
RbSrY ZrNbMoTcRuRhPdAgCdInSnSbTeIXe
CsBaLa*HfTaWReOsIrPtAuHgTlPbBiPoAtRn
FrRaAc**RfDbSgBhHsMtDsRgCnNhFlMcLvTsOg
 
 *CePrNdPmSmEuGdTbDyHoErTmYbLu
 **ThPaUNpPuAmCmBkCfEsFmMdNoLr
  Quantity elements
  Essential trace elements
  Deemed essential trace element by U.S., not by European Union
  Suggested function from deprivation effects or active metabolic handling, but no clearly-identified biochemical function in humans
  Limited circumstantial evidence for trace benefits or biological action in mammals
  No evidence for biological action in mammals, but essential in some lower organisms.
(In the case of lanthanum, the definition of an essential nutrient as being indispensable and irreplaceable is not completely applicable due to the extreme similarity of the lanthanides. Thus Ce, Pr, and Nd may be substituted for La without ill effects for organisms using La, and the smaller Sm, Eu, and Gd may also be similarly substituted but cause slower growth.)

History

Mendeleev's 1869 periodic table: An experiment on a system of elements. Based on their atomic weights and chemical similarities. Mendeleev's 1869 periodic table.svg
Mendeleev's 1869 periodic table: An experiment on a system of elements. Based on their atomic weights and chemical similarities.

Evolving definitions

The concept of an "element" as an undivisible substance has developed through three major historical phases: Classical definitions (such as those of the ancient Greeks), chemical definitions, and atomic definitions.

Classical definitions

Ancient philosophy posited a set of classical elements to explain observed patterns in nature. These elements originally referred to earth , water , air and fire rather than the chemical elements of modern science.

The term 'elements' (stoicheia) was first used by the Greek philosopher Plato in about 360 BCE in his dialogue Timaeus, which includes a discussion of the composition of inorganic and organic bodies and is a speculative treatise on chemistry. Plato believed the elements introduced a century earlier by Empedocles were composed of small polyhedral forms: tetrahedron (fire), octahedron (air), icosahedron (water), and cube (earth). [27] [28]

Aristotle, c. 350 BCE, also used the term stoicheia and added a fifth element called aether, which formed the heavens. Aristotle defined an element as:

Element – one of those bodies into which other bodies can decompose, and that itself is not capable of being divided into other. [29]

Chemical definitions

In 1661, Robert Boyle proposed his theory of corpuscularism which favoured the analysis of matter as constituted by irreducible units of matter (atoms) and, choosing to side with neither Aristotle's view of the four elements nor Paracelsus' view of three fundamental elements, left open the question of the number of elements. [30] The first modern list of chemical elements was given in Antoine Lavoisier's 1789 Elements of Chemistry , which contained thirty-three elements, including light and caloric. [31] By 1818, Jöns Jakob Berzelius had determined atomic weights for forty-five of the forty-nine then-accepted elements. Dmitri Mendeleev had sixty-six elements in his periodic table of 1869.

Dmitri Mendeleev DIMendeleevCab.jpg
Dmitri Mendeleev

From Boyle until the early 20th century, an element was defined as a pure substance that could not be decomposed into any simpler substance. [30] Put another way, a chemical element cannot be transformed into other chemical elements by chemical processes. Elements during this time were generally distinguished by their atomic weights, a property measurable with fair accuracy by available analytical techniques.

Atomic definitions

Henry Moseley Henry Moseley.jpg
Henry Moseley

The 1913 discovery by English physicist Henry Moseley that the nuclear charge is the physical basis for an atom's atomic number, further refined when the nature of protons and neutrons became appreciated, eventually led to the current definition of an element based on atomic number (number of protons per atomic nucleus). The use of atomic numbers, rather than atomic weights, to distinguish elements has greater predictive value (since these numbers are integers), and also resolves some ambiguities in the chemistry-based view due to varying properties of isotopes and allotropes within the same element. Currently, IUPAC defines an element to exist if it has isotopes with a lifetime longer than the 10−14 seconds it takes the nucleus to form an electronic cloud. [32]

By 1914, seventy-two elements were known, all naturally occurring. [33] The remaining naturally occurring elements were discovered or isolated in subsequent decades, and various additional elements have also been produced synthetically, with much of that work pioneered by Glenn T. Seaborg. In 1955, element 101 was discovered and named mendelevium in honor of D.I. Mendeleev, the first to arrange the elements in a periodic manner. Most recently, the synthesis of element 118 (since named oganesson) was reported in October 2006, and the synthesis of element 117 (tennessine) was reported in April 2010. [34]

Discovery and recognition of various elements

Ten materials familiar to various prehistoric cultures are now known to be chemical elements: Carbon, copper, gold, iron, lead, mercury, silver, sulfur, tin, and zinc. Three additional materials now accepted as elements, arsenic, antimony, and bismuth, were recognized as distinct substances prior to 1500 AD. Phosphorus, cobalt, and platinum were isolated before 1750.

Most of the remaining naturally occurring chemical elements were identified and characterized by 1900, including:

Elements isolated or produced since 1900 include:

Recently discovered elements

The first transuranium element (element with atomic number greater than 92) discovered was neptunium in 1940. Since 1999 claims for the discovery of new elements have been considered by the IUPAC/IUPAP Joint Working Party. As of January 2016, all 118 elements have been confirmed as discovered by IUPAC. The discovery of element 112 was acknowledged in 2009, and the name copernicium and the atomic symbol Cn were suggested for it. [35] The name and symbol were officially endorsed by IUPAC on 19 February 2010. [36] The heaviest element that is believed to have been synthesized to date is element 118, oganesson, on 9 October 2006, by the Flerov Laboratory of Nuclear Reactions in Dubna, Russia. [12] [37] Tennessine, element 117 was the latest element claimed to be discovered, in 2009. [38] On 28 November 2016, scientists at the IUPAC officially recognized the names for four of the newest chemical elements, with atomic numbers 113, 115, 117, and 118. [39] [40]

List of the 118 known chemical elements

The following sortable table shows the 118 known chemical elements.

Note that the densities of synthetic elements depend on the isotope.

List of chemical elements
Z [upper-roman 1] Symbol Element Origin of name [41] [42] Group Period Atomic weight [43] [44] ( u (±) ) Density ( g / cm3 ) Melt ( K ) [45] Boil (K) C [upper-roman 1] ( J / g  · K ) χ [upper-roman 1] Abundance in Earth's crust [upper-roman 2] (mg/kg)
1H Hydrogen Greek elements hydro- and -gen , meaning 'water-forming'111.008 [upper-roman 3] [upper-roman 4] [upper-roman 5] [upper-roman 6] 0.0000898814.0120.2814.3042.201400
2He Helium Greek hḗlios , 'sun'1814.002602(2) [upper-roman 3] [upper-roman 5] 0.0001785 [upper-roman 7] 4.225.1930.008
3Li Lithium Greek líthos , 'stone'126.94 [upper-roman 3] [upper-roman 4] [upper-roman 5] [upper-roman 8] [upper-roman 6] 0.534453.6915603.5820.9820
4Be Beryllium beryl, a mineral (ultimately from the name of Belur in southern India)229.0121831(5)1.85156027421.8251.572.8
5B Boron borax, a mineral (from Arabic bawraq )13210.81 [upper-roman 3] [upper-roman 4] [upper-roman 5] [upper-roman 6] 2.34234942001.0262.0410
6C Carbon Latin carbo , 'coal'14212.011 [upper-roman 3] [upper-roman 5] [upper-roman 6] 2.267380043000.7092.55200
7N Nitrogen Greek nítron and -gen , meaning 'niter-forming'15214.007 [upper-roman 3] [upper-roman 5] [upper-roman 6] 0.001250663.1577.361.043.0419
8O Oxygen Greek oxy- 'acid' and -gen , meaning 'acid-forming'16215.999 [upper-roman 3] [upper-roman 5] [upper-roman 6] 0.00142954.3690.200.9183.44461000
9F Fluorine Latin fluere , 'to flow'17218.998403163(6)0.00169653.5385.030.8243.98585
10Ne Neon Greek néon , 'new'18220.1797(6) [upper-roman 3] [upper-roman 4] 0.000899924.5627.071.030.005
11Na Sodium English soda (The symbol is derived from New Latin natrium , coined from German Natron , 'natron')1322.98976928(2)0.971370.8711561.2280.9323600
12Mg Magnesium Magnesia, a district of Eastern Thessaly in Greece 2324.305 [upper-roman 6] 1.73892313631.0231.3123300
13Al Aluminium alumina, from Latin alumen (gen. aluminis), 'bitter salt, alum'13326.9815384(3)2.698933.4727920.8971.6182300
14Si Silicon Latin silex , 'flint' (originally silicium)14328.085 [upper-roman 5] [upper-roman 6] 2.3296168735380.7051.9282000
15P Phosphorus Greek phōsphóros , 'light-bearing'15330.973761998(5)1.82317.305500.7692.191050
16S Sulfur Latin sulphur , 'brimstone'16332.06 [upper-roman 3] [upper-roman 5] [upper-roman 6] 2.067388.36717.870.712.58350
17Cl Chlorine Greek chlōrós , 'greenish yellow'17335.45 [upper-roman 3] [upper-roman 4] [upper-roman 5] [upper-roman 6] 0.003214171.6239.110.4793.16145
18Ar Argon Greek argós , 'idle' (because of its inertness)18339.948 [upper-roman 3] [upper-roman 5] [upper-roman 6] 0.001783783.8087.300.523.5
19K Potassium New Latin potassa , 'potash' (The symbol derives from Latin kalium )1439.0983(1)0.862336.5310320.7570.8220900
20Ca Calcium Latin calx , 'lime'2440.078(4) [upper-roman 3] 1.54111517570.647141500
21Sc Scandium Latin Scandia , 'Scandinavia'3444.955908(5)2.989181431090.5681.3622
22Ti Titanium Titans, the sons of the Earth goddess of Greek mythology4447.867(1)4.54194135600.5231.545650
23V Vanadium Vanadis, an Old Norse name for the Scandinavian goddess Freyja 5450.9415(1)6.11218336800.4891.63120
24Cr Chromium Greek chróma , 'colour'6451.9961(6)7.15218029440.4491.66102
25Mn Manganese corrupted from magnesia negra ; see Magnesium 7454.938043(2)7.44151923340.4791.55950
26Fe Iron English word (The symbol derives from Latin ferrum )8455.845(2)7.874181131340.4491.8356300
27Co Cobalt German Kobold , 'goblin'9458.933194(3)8.86176832000.4211.8825
28Ni Nickel Nickel, a mischievous sprite of German miner mythology10458.6934(4)8.912172831860.4441.9184
29Cu Copper English word, from Latin cuprum , from Ancient Greek Kýpros 'Cyprus'11463.546(3) [upper-roman 5] 8.961357.7728350.3851.960
30Zn Zinc Most likely from German Zinke , 'prong' or 'tooth', though some suggest Persian sang , 'stone'12465.38(2)7.134692.8811800.3881.6570
31Ga Gallium Latin Gallia , 'France'13469.723(1)5.907302.914626730.3711.8119
32Ge Germanium Latin Germania , 'Germany'14472.630(8)5.3231211.4031060.322.011.5
33As Arsenic French arsenic , from Greek arsenikón 'yellow arsenic' (influenced by arsenikós , 'masculine' or 'virile'), from a West Asian wanderword ultimately from Old Iranian *zarniya-ka, 'golden'15474.921595(6)5.7761090 [upper-roman 9] 8870.3292.181.8
34Se Selenium Greek selḗnē , 'moon'16478.971(8) [upper-roman 5] 4.8094539580.3212.550.05
35Br Bromine Greek brômos , 'stench'17479.904 [upper-roman 6] 3.122265.8332.00.4742.962.4
36Kr Krypton Greek kryptós , 'hidden'18483.798(2) [upper-roman 3] [upper-roman 4] 0.003733115.79119.930.24831×10−4
37Rb Rubidium Latin rubidus , 'deep red'1585.4678(3) [upper-roman 3] 1.532312.469610.3630.8290
38Sr Strontium Strontian, a village in Scotland 2587.62(1) [upper-roman 3] [upper-roman 5] 2.64105016550.3010.95370
39Y Yttrium Ytterby, a village in Sweden 3588.90584(1)4.469179936090.2981.2233
40Zr Zirconium zircon, a mineral4591.224(2) [upper-roman 3] 6.506212846820.2781.33165
41Nb Niobium Niobe, daughter of king Tantalus from Greek mythology5592.90637(1)8.57275050170.2651.620
42Mo Molybdenum Greek molýbdaina, 'piece of lead', from mólybdos , 'lead'6595.95(1) [upper-roman 3] 10.22289649120.2512.161.2
43Tc Technetium Greek tekhnētós , 'artificial'75[98] [upper-roman 10] 11.5243045381.9~ 3×10−9 [upper-roman 11]
44Ru Ruthenium New Latin Ruthenia , 'Russia'85101.07(2) [upper-roman 3] 12.37260744230.2382.20.001
45Rh Rhodium Greek rhodóeis , 'rose-coloured', from rhódon, 'rose'95102.90549(2)12.41223739680.2432.280.001
46Pd Palladium the asteroid Pallas, considered a planet at the time105106.42(1) [upper-roman 3] 12.021828.0532360.2442.20.015
47Ag Silver English word (The symbol derives from Latin argentum )115107.8682(2) [upper-roman 3] 10.5011234.9324350.2351.930.075
48Cd Cadmium New Latin cadmia , from King Kadmos 125112.414(4) [upper-roman 3] 8.69594.2210400.2321.690.159
49In Indium Latin indicum , 'indigo' (colour found in its spectrum)135114.818(1)7.31429.7523450.2331.780.25
50Sn Tin English word (The symbol derives from Latin stannum )145118.710(7) [upper-roman 3] 7.287505.0828750.2281.962.3
51Sb Antimony Latin antimonium , the origin of which is uncertain: folk etymologies suggest it is derived from Greek antí ('against') + mónos ('alone'), or Old French anti-moine , 'Monk's bane', but it could plausibly be from or related to Arabic ʾiṯmid , 'antimony', reformatted as a Latin word. (The symbol derives from Latin stibium 'stibnite'.)155121.760(1) [upper-roman 3] 6.685903.7818600.2072.050.2
52Te Tellurium Latin tellus , 'the ground, earth'165127.60(3) [upper-roman 3] 6.232722.6612610.2022.10.001
53I Iodine French iode , from Greek ioeidḗs , 'violet')175126.90447(3)4.93386.85457.40.2142.660.45
54Xe Xenon Greek xénon , neuter form of xénos 'strange'185131.293(6) [upper-roman 3] [upper-roman 4] 0.005887161.4165.030.1582.63×10−5
55Cs Caesium Latin caesius , 'sky-blue'16132.90545196(6)1.873301.599440.2420.793
56Ba Barium Greek barýs , 'heavy'26137.327(7)3.594100021700.2040.89425
57La Lanthanum Greek lanthánein , 'to lie hidden'36138.90547(7) [upper-roman 3] 6.145119337370.1951.139
58Ce Cerium the dwarf planet Ceres, considered a planet at the time6140.116(1) [upper-roman 3] 6.77106837160.1921.1266.5
59Pr Praseodymium Greek prásios dídymos , 'green twin'6140.90766(1)6.773120837930.1931.139.2
60Nd Neodymium Greek néos dídymos , 'new twin'6144.242(3) [upper-roman 3] 7.007129733470.191.1441.5
61Pm Promethium Prometheus of Greek mythology6[145] [upper-roman 10] 7.26131532731.132×10−19 [upper-roman 11]
62Sm Samarium samarskite, a mineral named after Colonel Vasili Samarsky-Bykhovets, Russian mine official6150.36(2) [upper-roman 3] 7.52134520670.1971.177.05
63Eu Europium Europe 6151.964(1) [upper-roman 3] 5.243109918020.1821.22
64Gd Gadolinium gadolinite, a mineral named after Johan Gadolin, Finnish chemist, physicist and mineralogist6157.25(3) [upper-roman 3] 7.895158535460.2361.26.2
65Tb Terbium Ytterby, a village in Sweden6158.925354(8)8.229162935030.1821.21.2
66Dy Dysprosium Greek dysprósitos , 'hard to get'6162.500(1) [upper-roman 3] 8.55168028400.171.225.2
67Ho Holmium New Latin Holmia, 'Stockholm'6164.930328(7)8.795173429930.1651.231.3
68Er Erbium Ytterby, a village in Sweden6167.259(3) [upper-roman 3] 9.066180231410.1681.243.5
69Tm Thulium Thule, the ancient name for an unclear northern location6168.934218(6)9.321181822230.161.250.52
70Yb Ytterbium Ytterby, a village in Sweden6173.045(10) [upper-roman 3] 6.965109714690.1551.13.2
71Lu Lutetium Latin Lutetia , 'Paris'6174.9668(1) [upper-roman 3] 9.84192536750.1541.270.8
72Hf Hafnium New Latin Hafnia, 'Copenhagen' (from Danish havn )46178.49(2)13.31250648760.1441.33
73Ta Tantalum King Tantalus, father of Niobe from Greek mythology56180.94788(2)16.654329057310.141.52
74W Tungsten Swedish tung sten , 'heavy stone' (The symbol is from wolfram, the old name of the tungsten mineral wolframite)66183.84(1)19.25369558280.1322.361.3
75Re Rhenium Latin Rhenus , 'the Rhine'76186.207(1)21.02345958690.1371.97×10−4
76Os Osmium Greek osmḗ , 'smell'86190.23(3) [upper-roman 3] 22.61330652850.132.20.002
77Ir Iridium Iris, the Greek goddess of the rainbow96192.217(2)22.56271947010.1312.20.001
78Pt Platinum Spanish platina , 'little silver', from plata 'silver'106195.084(9)21.462041.440980.1332.280.005
79Au Gold English word (The symbol derives from Latin aurum )116196.966570(4)19.2821337.3331290.1292.540.004
80Hg Mercury Mercury, Roman god of commerce, communication, and luck, known for his speed and mobility (The symbol is from the element's Latin name hydrargyrum , derived from Greek hydrárgyros , 'water-silver')126200.592(3)13.5336234.43629.880.1420.085
81Tl Thallium Greek thallós , 'green shoot or twig'136204.38 [upper-roman 6] 11.8557717460.1291.620.85
82Pb Lead English word (The symbol derives from Latin plumbum )146207.2(1) [upper-roman 3] [upper-roman 5] 11.342600.6120220.1291.8714
83Bi Bismuth German Wismut, from weiß Masse 'white mass', unless from Arabic156208.98040(1) [upper-roman 10] 9.807544.718370.1222.020.009
84Po Polonium Latin Polonia , 'Poland' (the home country of Marie Curie)166[209] [upper-roman 10] 9.3252712352.02×10−10 [upper-roman 11]
85At Astatine Greek ástatos , 'unstable'176[210] [upper-roman 10] 75756102.23×10−20 [upper-roman 11]
86Rn Radon radium 186[222] [upper-roman 10] 0.00973202211.30.0942.24×10−13 [upper-roman 11]
87Fr Francium France 17[223] [upper-roman 10] 1.873009500.7~ 1×10−18 [upper-roman 11]
88Ra Radium French radium, from Latin radius , 'ray'27[226] [upper-roman 10] 5.597320100.0940.99×10−7 [upper-roman 11]
89Ac Actinium Greek aktís , 'ray'37[227] [upper-roman 10] 10.07132334710.121.15.5×10−10 [upper-roman 11]
90Th Thorium Thor, the Scandinavian god of thunder7232.0377(4) [upper-roman 10] [upper-roman 3] 11.72211550610.1131.39.6
91Pa Protactinium proto- (from Greek prôtos , 'first, before') + actinium, which is produced through the radioactive decay of protactinium7231.03588(1) [upper-roman 10] 15.37184143001.51.4×10−6 [upper-roman 11]
92U Uranium Uranus, the seventh planet in the Solar System7238.02891(3) [upper-roman 10] 18.951405.344040.1161.382.7
93Np Neptunium Neptune, the eighth planet in the Solar System7[237] [upper-roman 10] 20.4591742731.36 3×10−12 [upper-roman 11]
94Pu Plutonium the dwarf planet Pluto, considered the ninth planet in the Solar System at the time7[244] [upper-roman 10] 19.84912.535011.28 3×10−11 [upper-roman 11]
95Am Americium The Americas, as the element was first synthesised on the continent, by analogy with europium 7[243] [upper-roman 10] 13.69144928801.130 [upper-roman 12]
96Cm Curium Pierre Curie and Marie Curie, French physicists and chemists7[247] [upper-roman 10] 13.51161333831.280 [upper-roman 12]
97Bk Berkelium Berkeley, California, where the element was first synthesised, by analogy with terbium 7[247] [upper-roman 10] 14.79125929001.30 [upper-roman 12]
98Cf Californium California, where the element was first synthesised7[251] [upper-roman 10] 15.11173(1743) [upper-roman 13] 1.30 [upper-roman 12]
99Es Einsteinium Albert Einstein, German physicist7[252] [upper-roman 10] 8.841133(1269) [upper-roman 13] 1.30 [upper-roman 12]
100Fm Fermium Enrico Fermi, Italian physicist7[257] [upper-roman 10] (9.7) [upper-roman 13] (1125) [upper-roman 13] 1.30 [upper-roman 12]
101Md Mendelevium Dmitri Mendeleev, Russian chemist and inventor who proposed the periodic table 7[258] [upper-roman 10] (10.3) [upper-roman 13] (1100) [upper-roman 13] 1.30 [upper-roman 12]
102No Nobelium Alfred Nobel, Swedish chemist and engineer7[259] [upper-roman 10] (9.9) [upper-roman 13] (1100) [upper-roman 13] 1.30 [upper-roman 12]
103Lr Lawrencium Ernest O. Lawrence, American physicist7[266] [upper-roman 10] (15.6) [upper-roman 13] (1900) [upper-roman 13] 1.30 [upper-roman 12]
104Rf Rutherfordium Ernest Rutherford, British chemist and physicist47[267] [upper-roman 10] (23.2) [upper-roman 13] (2400) [upper-roman 13] (5800) [upper-roman 13] 0 [upper-roman 12]
105Db Dubnium Dubna, a town in Russia where the Joint Institute for Nuclear Research is located57[268] [upper-roman 10] (29.3) [upper-roman 13] 0 [upper-roman 12]
106Sg Seaborgium Glenn T. Seaborg, American chemist67[269] [upper-roman 10] (35.0) [upper-roman 13] 0 [upper-roman 12]
107Bh Bohrium Niels Bohr, Danish physicist77[270] [upper-roman 10] (37.1) [upper-roman 13] 0 [upper-roman 12]
108Hs Hassium New Latin Hassia, 'Hesse' (a state in Germany)87[270] [upper-roman 10] (40.7) [upper-roman 13] 0 [upper-roman 12]
109Mt Meitnerium Lise Meitner, Austrian physicist97[278] [upper-roman 10] (37.4) [upper-roman 13] 0 [upper-roman 12]
110Ds Darmstadtium Darmstadt, Germany, where the element was first synthesised107[281] [upper-roman 10] (34.8) [upper-roman 13] 0 [upper-roman 12]
111Rg Roentgenium Wilhelm Conrad Röntgen, German physicist117[282] [upper-roman 10] (28.7) [upper-roman 13] 0 [upper-roman 12]
112Cn Copernicium Nicolaus Copernicus, Polish astronomer127[285] [upper-roman 10] (23.7) [upper-roman 13] ~357 [upper-roman 14] 0 [upper-roman 12]
113Nh Nihonium Japanese Nihon , 'Japan' (where the element was first synthesised)137[286] [upper-roman 10] (16) [upper-roman 13] (700) [upper-roman 13] (1400) [upper-roman 13] 0 [upper-roman 12]
114Fl Flerovium Flerov Laboratory of Nuclear Reactions, part of JINR, where the element was synthesised; itself named after Georgy Flyorov, Russian physicist147[289] [upper-roman 10] (14) [upper-roman 13] ~2100 [upper-roman 12]
115Mc Moscovium Moscow Oblast, Russia, where the element was first synthesised157[290] [upper-roman 10] (13.5) [upper-roman 13] (700) [upper-roman 13] (1400) [upper-roman 13] 0 [upper-roman 12]
116Lv Livermorium Lawrence Livermore National Laboratory in Livermore, California, which collaborated with JINR on its synthesis167[293] [upper-roman 10] (12.9) [upper-roman 13] (709) [upper-roman 13] (1085) [upper-roman 13] 0 [upper-roman 12]
117Ts Tennessine Tennessee, United States177[294] [upper-roman 10] (7.2) [upper-roman 13] (723) [upper-roman 13] (883) [upper-roman 13] 0 [upper-roman 12]
118Og Oganesson Yuri Oganessian, Russian physicist187[294] [upper-roman 10] (5.0) [upper-roman 13] [upper-roman 15] (350) [upper-roman 13] 0 [upper-roman 12]

Notes

  1. 1 2 3 Z is the standard symbol for atomic number; C is the standard symbol for heat capacity; and χ is the standard symbol for electronegativity on the Pauling scale.
  2. Unless otherwise indicated, elements are primordial – they occur naturally, and not through decay.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 The isotopic composition of this element varies in some geological specimens, and the variation may exceed the uncertainty stated in the table.
  4. 1 2 3 4 5 6 7 The isotopic composition of the element can vary in commercial materials, which can cause the atomic weight to deviate significantly from the given value.
  5. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 The isotopic composition varies in terrestrial material such that a more precise atomic weight can not be given.
  6. 1 2 3 4 5 6 7 8 9 10 11 12 13 The value listed is the conventional atomic-weight value suitable for trade and commerce. The actual value may differ depending on the isotopic composition of the sample. Since 2009, IUPAC provides the standard atomic-weight values for these elements using the interval notation. The corresponding standard atomic weights are:
    • Hydrogen: [1.00784, 1.00811]
    • Lithium: [6.938, 6.997]
    • Boron: [10.806, 10.821]
    • Carbon: [12.0096, 12.0116]
    • Nitrogen: [14.00643, 14.00728]
    • Oxygen: [15.99903, 15.99977]
    • Magnesium: [24.304, 24.307]
    • Silicon: [28.084, 28.086]
    • Sulfur: [32.059, 32.076]
    • Chlorine: [35.446, 35.457]
    • Argon: [39.792, 39.963]
    • Bromine: [79.901, 79.907]
    • Thallium: [204.382, 204.385]
  7. Helium does not solidify at a pressure of one atmosphere. Helium can only solidify at pressures above 25 atmospheres, which corresponds to a melting point of absolute zero.
  8. The atomic weight of commercial lithium can vary between 6.939 and 6.996—analysis of the specific material is necessary to find a more accurate value.
  9. This element sublimes at one atmosphere of pressure.
  10. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 The element does not have any stable nuclides, and a value in brackets, e.g. [209], indicates the mass number of the longest-lived isotope of the element. However, four such elements, bismuth, thorium, protactinium, and uranium, have characteristic terrestrial isotopic compositions, and thus their standard atomic weights are given.
  11. 1 2 3 4 5 6 7 8 9 10 11 This element is transient – it occurs only through decay.
  12. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 This element is synthetic – the transuranic elements 95 and above do not occur naturally, but they can all be produced artificially.
  13. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 The value has not been precisely measured, usually because of the element's short half-life; the value given in parentheses is a prediction.
  14. With error bars: 357+112
    −108
     K.
  15. This predicted value is for liquid oganesson, not gaseous oganesson.

See also

Related Research Articles

Atomic number number of protons found in the nucleus of an atom

The atomic number or proton number of a chemical element is the number of protons found in the nucleus of an atom. It is identical to the charge number of the nucleus. The atomic number uniquely identifies a chemical element. In an uncharged atom, the atomic number is also equal to the number of electrons.

The periodic table is a tabular method of displaying the chemical elements. It can show much information, after name, symbol and atomic number. Also, for each element mean atomic mass value for the natural isotopic composition of each element can be noted. The two layout forms originate from two graphic forms of presentation of the same periodic table. Historically, when the f-block was identified it was drawn below the existing table, with markings for its in-table location. Also, a common presentation is to put all 15 lanthanide and actinide columns below, while the f-block only has 14 columns. One lanthanide and actinide each are d-block elements, belonging to group 3 with scandium and yttrium, though whether these are the first of each series or the last has been disputed. The tables below show lanthanum and actinium as group 3 elements, as this is the more common form in the literature.

Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons, primarily protons and neutrons. The first nuclei were formed about three minutes after the Big Bang, through the process called Big Bang nucleosynthesis. Seventeen minutes later the universe had cooled to a point at which these processes ended, so only the fastest and simplest reactions occurred, leaving our universe containing about 75% hydrogen, 24% helium, and traces of other elements such as lithium and the hydrogen isotope deuterium. The universe still has approximately the same composition today.

Symbol (chemistry)

In relation to the chemical elements, a symbol is a code 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.

Period (periodic table) row in the periodic table of elements

A period in the periodic table is a row of chemical elements. All elements in a row have the same number of electron shells. Each next element in a period has one more proton and is less metallic than its predecessor. Arranged this way, groups of elements in the same column have similar chemical and physical properties, reflecting the periodic law. For example, the alkali metals lie in the first column and share similar properties, such as high reactivity and the tendency to lose one electron to arrive at a noble-gas electronic configuration. As of 2016, a total of 118 elements have been discovered and confirmed.

Nuclide atomic species characterized by the specific constitution of its nucleus: mass number, atomic number, and, where long-enough-lived to observe, the nuclear energy state

A nuclide is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and its nuclear energy state.

A period 6 element is one of the chemical elements in the sixth row (or period) of the periodic table of the elements, including the lanthanides. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The sixth period contains 32 elements, tied for the most with period 7, beginning with caesium and ending with radon. Lead is currently the last stable element; all subsequent elements are radioactive. For bismuth, however, its only primordial isotope, 209Bi, has a half-life of more than 1019 years, over a billion times longer than the current age of the universe. As a rule, period 6 elements fill their 6s shells first, then their 4f, 5d, and 6p shells, in that order; however, there are exceptions, such as gold.

A period 2 element is one of the chemical elements in the second row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases; a new row is started when chemical behavior begins to repeat, creating columns of elements with similar properties.

A period 7 element is one of the chemical elements in the seventh row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The seventh period contains 32 elements, tied for the most with period 6, beginning with francium and ending with oganesson, the heaviest element currently discovered. As a rule, period 7 elements fill their 7s shells first, then their 5f, 6d, and 7p shells, in that order; however, there are exceptions, such as plutonium.

The mass number (symbol A, from the German word Atomgewicht, also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. It determines the atomic mass of atoms. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion. The mass number is different for each different isotope of a chemical element. This is not the same as the atomic number which denotes the number of protons in a nucleus, and thus uniquely identifies an element. Hence, the difference between the mass number and the atomic number gives the number of neutrons in a given nucleus: .

Isotopes of hydrogen

Hydrogen (1H) has three naturally occurring isotopes, sometimes denoted 1H, 2H, and 3H. The first two of these are stable, while 3H has a half-life of 12.32 years. All heavier isotopes are synthetic and have a half-life less than one zeptosecond. Of these, 5H is the most stable, and 7H is the least.

Natural nitrogen (7N) consists of two stable isotopes, nitrogen-14, which makes up the vast majority of naturally occurring nitrogen, and nitrogen-15, which is less common. Fourteen radioactive isotopes (radioisotopes) have also been found so far, with atomic masses ranging from 10 to 25, and one nuclear isomer, 11mN. All of these radioisotopes are short-lived, with the longest-lived one being nitrogen-13 with a half-life of 9.965 minutes. All of the others have half-lives below 7.15 seconds, with most of these being below five-eighths of a second. Most of the isotopes with atomic mass numbers below 14 decay to isotopes of carbon, while most of the isotopes with masses above 15 decay to isotopes of oxygen. The shortest-lived known isotope is nitrogen-10, with a half-life of about 200 yoctoseconds.

Although there are nine known isotopes of helium (2He), only helium-3 and helium-4 are stable. All radioisotopes are short-lived, the longest-lived being 6
He
with a half-life of 806.7 milliseconds. The least stable is 5
He
, with a half-life of 7.6×10−22 s, although it is possible that 2
He
has an even shorter half-life.

Table of nuclides

A table of nuclides or chart of nuclides is a two-dimensional graph in which one axis represents the number of neutrons and the other represents the number of protons in an atomic nucleus. Each point plotted on the graph thus represents the nuclide of a real or hypothetical chemical element. This system of ordering nuclides can offer a greater insight into the characteristics of isotopes than the better-known periodic table, which shows only elements instead of each of their isotopes.

Atomic mass mass of an atom in unified atomic mass units

The atomic mass (ma) is the mass of an atom. Its unit is the unified atomic mass units where 1 unified atomic mass unit is defined as ​112 of the mass of a single carbon-12 atom, at rest. For atoms, the protons and neutrons of the nucleus account for nearly all of the total mass, and the atomic mass measured in u has nearly the same value as the mass number.

Primordial nuclide

In geochemistry, geophysics and geonuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the interstellar medium from which the solar system was formed, and were formed in, or after, the Big Bang, by nucleosynthesis in stars and supernovae followed by mass ejection, by cosmic ray spallation, and potentially from other processes. They are the stable nuclides plus the long-lived fraction of radionuclides surviving in the primordial solar nebula through planet accretion until the present. Only 286 such nuclides are known.

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Further reading