|Pronunciation|| / /|
|Appearance||silvery gray; with a pale yellow tint|
|Standard atomic weight Ar, std(Ba)||137.327(7)|
|Barium in the periodic table|
|Atomic number (Z)||56|
|Group||group 2 (alkaline earth metals)|
|Element category||Alkaline earth metal|
|Electron configuration||[ Xe ] 6s2|
Electrons per shell
|2, 8, 18, 18, 8, 2|
|Phase at STP||solid|
|Melting point||1000 K (727 °C,1341 °F)|
|Boiling point||2118 K(1845 °C,3353 °F)|
|Density (near r.t.)||3.51 g/cm3|
|when liquid (at m.p.)||3.338 g/cm3|
|Heat of fusion||7.12 kJ/mol|
|Heat of vaporization||142 kJ/mol|
|Molar heat capacity||28.07 J/(mol·K)|
| Vapor pressure |
|Oxidation states||+1, +2 (a strongly basic oxide)|
|Electronegativity||Pauling scale: 0.89|
|Atomic radius||empirical:222 pm|
|Covalent radius||215±11 pm|
|Van der Waals radius||268 pm|
|Spectral lines of barium|
|Crystal structure|| body-centered cubic (bcc)|
|Speed of sound thin rod||1620 m/s(at 20 °C)|
|Thermal expansion||20.6 µm/(m·K)(at 25 °C)|
|Thermal conductivity||18.4 W/(m·K)|
|Electrical resistivity||332 nΩ·m(at 20 °C)|
|Magnetic susceptibility||+20.6·10−6 cm3/mol|
|Young's modulus||13 GPa|
|Shear modulus||4.9 GPa|
|Bulk modulus||9.6 GPa|
|Discovery||Carl Wilhelm Scheele (1772)|
|First isolation||Humphry Davy (1808)|
|Main isotopes of barium|
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.
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.
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.
The atomic number or proton number of a chemical element is the number of protons found in the nucleus of every atom of that element. The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus. In an uncharged atom, the atomic number is also equal to the number of electrons.
The most common naturally occurring minerals of barium are barite (now called baryte) (barium sulfate, BaSO4) and witherite (barium carbonate, BaCO3), both insoluble in water. The name barium originates from the alchemical derivative "baryta", from Greek βαρύς (barys), meaning "heavy." Baric is the adjectival form of barium. Barium was identified as a new element in 1774, but not reduced to a metal until 1808 with the advent of electrolysis.
Baryte or barite (, ) is a mineral consisting of barium sulfate (BaSO4). Baryte is generally white or colorless, and is the main source of barium. The baryte group consists of baryte, celestine (strontium sulfate), anglesite (lead sulfate), and anhydrite (calcium sulfate). Baryte and celestine form a solid solution (Ba,Sr)SO4.
Barium sulfate (or sulphate) is the inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and materials prepared from it. The white opaque appearance and its high density are exploited in its main applications.
Witherite is a barium carbonate mineral, BaCO3, in the aragonite group. Witherite crystallizes in the orthorhombic system and virtually always is twinned. The mineral is colorless, milky-white, grey, pale-yellow, green, to pale-brown. The specific gravity is 4.3, which is high for a translucent mineral. It fluoresces light blue under both long- and short-wave UV light, and is phosphorescent under short-wave UV light.
Barium has few industrial applications. Historically, it was used as a getter for vacuum tubes and in oxide form as the emissive coating on indirectly heated cathodes. It is a component of YBCO (high-temperature superconductors) and electroceramics, and is added to steel and cast iron to reduce the size of carbon grains within the microstructure. Barium compounds are added to fireworks to impart a green color. Barium sulfate is used as an insoluble additive to oil well drilling fluid, as well as in a purer form, as X-ray radiocontrast agents for imaging the human gastrointestinal tract. The soluble barium ion and soluble compounds are poisonous, and have been used as rodenticides.
A getter is a deposit of reactive material that is placed inside a vacuum system, for the purpose of completing and maintaining the vacuum. When gas molecules strike the getter material, they combine with it chemically or by absorption. Thus the getter removes small amounts of gas from the evacuated space.
In electronics, a vacuum tube, an electron tube, or valve or, colloquially, a tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
Yttrium barium copper oxide (YBCO) is a family of crystalline chemical compounds, famous for displaying high-temperature superconductivity. It includes the first material ever discovered to become superconducting above the boiling point of liquid nitrogen (77 K) at about 92 K. Many YBCO compounds have the general formula YBa2Cu3O7−x (also known as Y123), although materials with other Y:Ba:Cu ratios exist, such as YBa2Cu4Oy (Y124) or Y2Ba4Cu7Oy (Y247). At present, there is no singularly recognised theory for high-temperature superconductivity.
Barium is a soft, silvery-white metal, with a slight golden shade when ultrapure. 2 The silvery-white color of barium metal rapidly vanishes upon oxidation in air yielding a dark gray oxide layer. Barium has a medium specific weight and good electrical conductivity. Ultrapure barium is very difficult to prepare, and therefore many properties of barium have not been accurately measured yet. :2:
Redox is a type of chemical reaction in which the oxidation states of atoms are changed. Redox reactions are characterized by the transfer of electrons between chemical species, most often with one species undergoing oxidation while another species undergoes reduction. The chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. In other words:
Barium oxide, BaO, baria, is a white hygroscopic non-flammable compound. It has a cubic structure and is used in cathode ray tubes, crown glass, and catalysts. It is harmful to human skin and if swallowed in large quantity causes irritation. Excessive quantities of barium oxide may lead to death.
The specific weight is the weight per unit volume of a material. The symbol of specific weight is γ.
At room temperature and pressure, barium has a body-centered cubic structure, with a barium–barium distance of 503 picometers, expanding with heating at a rate of approximately 1.8×10−5/°C. :2 It is a very soft metal with a Mohs hardness of 1.25. :2 Its melting temperature of 1,000 K (730 °C; 1,340 °F) :4–43 is intermediate between those of the lighter strontium (1,050 K or 780 °C or 1,430 °F) :4–86 and heavier radium (973 K or 700 °C or 1,292 °F); :4–78 however, its boiling point of 2,170 K (1,900 °C; 3,450 °F) exceeds that of strontium (1,655 K or 1,382 °C or 2,519 °F). :4–86 The density (3.62 g/cm3) :4–43 is again intermediate between those of strontium (2.36 g/cm3) :4–86 and radium (≈5 g/cm3). :4–78
Barium is chemically similar to magnesium, calcium, and strontium, but even more reactive. It always exhibits the oxidation state of +2, except in a few rare and unstable molecular species that are only characterised in the gas phase such as BaF. 2 Reactions with chalcogens are highly exothermic (release energy); the reaction with oxygen or air occurs at room temperature, and therefore barium is stored under oil or in an inert atmosphere. :2 Reactions with other nonmetals, such as carbon, nitrogen, phosphorus, silicon, and hydrogen, are generally exothermic and proceed upon heating. :2–3 Reactions with water and alcohols are very exothermic and release hydrogen gas: :3:
The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. It consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioactive element polonium (Po). The chemically uncharacterized synthetic element livermorium (Lv) is predicted to be a chalcogen as well. Often, oxygen is treated separately from the other chalcogens, sometimes even excluded from the scope of the term "chalcogen" altogether, due to its very different chemical behavior from sulfur, selenium, tellurium, and polonium. The word "chalcogen" is derived from a combination of the Greek word khalkόs (χαλκός) principally meaning copper, and the Latinised Greek word genēs, meaning born or produced.
An exothermic reaction is a chemical reaction that releases energy through light or heat. It is the opposite of an endothermic reaction.
In chemistry, a nonmetal is a chemical element that mostly lacks the characteristics of a metal. Physically, a nonmetal tends to have a relatively low melting point, boiling point, and density. A nonmetal is typically brittle when solid and usually has poor thermal conductivity and electrical conductivity. Chemically, nonmetals tend to have relatively high ionization energy, electron affinity, and electronegativity. They gain or share electrons when they react with other elements and chemical compounds. Seventeen elements are generally classified as nonmetals: most are gases ; one is a liquid (bromine); and a few are solids. Metalloids such as boron, silicon, and germanium are sometimes counted as nonmetals.
Barium reacts with ammonia to form complexes such as Ba(NH3)6. 3:
The metal is readily attacked by most acids. Sulfuric acid is a notable exception because passivation stops the reaction by forming the insoluble barium sulfate on the surface.Barium combines with several metals, including aluminium, zinc, lead, and tin, forming intermetallic phases and alloys.
| O2−|| S2−|| F−|| Cl−|| SO2−|
Barium salts are typically white when solid and colorless when dissolved, and barium ions provide no specific coloring.They are denser than the strontium or calcium analogs, except for the halides (see table; zinc is given for comparison).
Barium hydroxide ("baryta") was known to alchemists, who produced it by heating barium carbonate. Unlike calcium hydroxide, it absorbs very little CO2 in aqueous solutions and is therefore insensitive to atmospheric fluctuations. This property is used in calibrating pH equipment.
Volatile barium compounds burn with a green to pale green flame, which is an efficient test to detect a barium compound. The color results from spectral lines at 455.4, 493.4, 553.6, and 611.1 nm. :3
Organobarium compounds are a growing field of knowledge: recently discovered are dialkylbariums and alkylhalobariums. 3:
Barium found in the Earth's crust is a mixture of seven primordial nuclides, barium-130, 132, and 134 through 138.Barium-130 undergoes very slow radioactive decay to xenon-130 by double beta plus decay, and barium-132 theoretically decays similarly to xenon-132, with half-lives a thousand times greater than the age of the Universe. The abundance is ≈0.1% that of natural barium. The radioactivity of these isotopes is so weak that they pose no danger to life.
Of the stable isotopes, barium-138 composes 71.7% of all barium; other isotopes have decreasing abundance with decreasing mass number.
In total, barium has about 40 known isotopes, ranging in mass between 114 and 153. The most stable artificial radioisotope is barium-133 with a half-life of approximately 10.51 years. Five other isotopes have half-lives longer than a day. Barium also has 10 meta states, of which barium-133m1 is the most stable with a half-life of about 39 hours.
Alchemists in the early Middle Ages knew about some barium minerals. Smooth pebble-like stones of mineral baryte were found in volcanic rock near Bologna, Italy, and so were called "Bologna stones." Alchemists were attracted to them because after exposure to light they would glow for years. 5The phosphorescent properties of baryte heated with organics were described by V. Casciorolus in 1602. :
Carl Scheele determined that baryte contained a new element in 1774, but could not isolate barium, only barium oxide. Johan Gottlieb Gahn also isolated barium oxide two years later in similar studies. Oxidized barium was at first called "barote" by Guyton de Morveau, a name that was changed by Antoine Lavoisier to baryta. Also in the 18th century, English mineralogist William Withering noted a heavy mineral in the lead mines of Cumberland, now known to be witherite. Barium was first isolated by electrolysis of molten barium salts in 1808 by Sir Humphry Davy in England.Davy, by analogy with calcium, named "barium" after baryta, with the "-ium" ending signifying a metallic element. Robert Bunsen and Augustus Matthiessen obtained pure barium by electrolysis of a molten mixture of barium chloride and ammonium chloride.
The production of pure oxygen in the Brin process was a large-scale application of barium peroxide in the 1880s, before it was replaced by electrolysis and fractional distillation of liquefied air in the early 1900s. In this process barium oxide reacts at 500–600 °C (932–1,112 °F) with air to form barium peroxide, which decomposes above 700 °C (1,292 °F) by releasing oxygen:
Barium sulfate was first applied as a radiocontrast agent in X-ray imaging of the digestive system in 1908.
The abundance of barium is 0.0425% in the Earth's crust and 13 µg/L in sea water. The primary commercial source of barium is baryte (also called barytes or heavy spar), a barium sulfate mineral. :5 with deposits in many parts of the world. Another commercial source, far less important than baryte, is witherite, a barium carbonate mineral. The main deposits are located in England, Romania, and the former USSR. :5
The baryte reserves are estimated between 0.7 and 2 billion tonnes. The maximum production, 8.3 million tonnes, was produced in 1981, but only 7–8% was used for barium metal or compounds. 5 Baryte production has risen since the second half of the 1990s from 5.6 million tonnes in 1996 to 7.6 in 2005 and 7.8 in 2011. China accounts for more than 50% of this output, followed by India (14% in 2011), Morocco (8.3%), US (8.2%), Turkey (2.5%), Iran and Kazakhstan (2.6% each).:
The mined ore is washed, crushed, classified, and separated from quartz. If the quartz penetrates too deeply into the ore, or the iron, zinc, or lead content is abnormally high, then froth flotation is used. The product is a 98% pure baryte (by mass); the purity should be no less than 95%, with a minimal content of iron and silicon dioxide. 7 It is then reduced by carbon to barium sulfide: :6:
The water-soluble barium sulfide is the starting point for other compounds: reacting BaS with oxygen produces the sulfate, with nitric acid the nitrate, with carbon dioxide the carbonate, and so on. 6 The nitrate can be thermally decomposed to yield the oxide. :6 Barium metal is produced by reduction with aluminium at 1,100 °C (2,010 °F). The intermetallic compound BaAl4 is produced first: :3:
BaAl4 is an intermediate reacted with barium oxide to produce the metal. Note that not all barium is reduced. 3:
The remaining barium oxide reacts with the formed aluminium oxide: 3:
and the overall reaction is 3:
Barium vapor is condensed and packed into molds in an atmosphere of argon. 3 This method is used commercially, yielding ultrapure barium. :3 Commonly sold barium is about 99% pure, with main impurities being strontium and calcium (up to 0.8% and 0.25%) and other contaminants contributing less than 0.1%. :4:
A similar reaction with silicon at 1,200 °C (2,190 °F) yields barium and barium metasilicate. :3 Electrolysis is not used because barium readily dissolves in molten halides and the product is rather impure. :3
The barium mineral, benitoite (barium titanium silicate), occurs as a very rare blue fluorescent gemstone, and is the official state gem of California.
Barium, as a metal or when alloyed with aluminium, is used to remove unwanted gases (gettering) from vacuum tubes, such as TV picture tubes. 4 Barium is suitable for this purpose because of its low vapor pressure and reactivity towards oxygen, nitrogen, carbon dioxide, and water; it can even partly remove noble gases by dissolving them in the crystal lattice. This application is gradually disappearing due to the rising popularity of the tubeless LCD and plasma sets. :4:
Other uses of elemental barium are minor and include an additive to silumin (aluminium–silicon alloys) that refines their structure, as well as 4:
Barium sulfate (the mineral baryte, BaSO4) is important to the petroleum industry as a drilling fluid in oil and gas wells. 4–5 The precipitate of the compound (called "blanc fixe", from the French for "permanent white") is used in paints and varnishes; as a filler in ringing ink, plastics, and rubbers; as a paper coating pigment; and in nanoparticles, to improve physical properties of some polymers, such as epoxies. :9:
Barium sulfate has a low toxicity and relatively high density of ca. 4.5 g/cm3 (and thus opacity to X-rays). For this reason it is used as a radiocontrast agent in X-ray imaging of the digestive system ("barium meals" and "barium enemas"). :4–5 Lithopone, a pigment that contains barium sulfate and zinc sulfide, is a permanent white with good covering power that does not darken when exposed to sulfides.
Other compounds of barium find only niche applications, limited by the toxicity of Ba2+ ions (barium carbonate is a rat poison), which is not a problem for the insoluble BaSO4.
|GHS Signal word||Danger|
|P231+232, P335+334, P370+378, P402+404|
|NFPA 704 (fire diamond)|
Because of the high reactivity of the metal, toxicological data are available only for compounds.Soluble barium compounds are poisonous. In low doses, barium ions act as a muscle stimulant, and higher doses affect the nervous system, causing cardiac irregularities, tremors, weakness, anxiety, shortness of breath, and paralysis. This toxicity may be caused by Ba2+ blocking potassium ion channels, which are critical to the proper function of the nervous system. Other organs damaged by water-soluble barium compounds (i.e., barium ions) are the eyes, immune system, heart, respiratory system, and skin causing, for example, blindness and sensitization.
Barium is not carcinogenic 9and does not bioaccumulate. Inhaled dust containing insoluble barium compounds can accumulate in the lungs, causing a benign condition called baritosis. The insoluble sulfate is nontoxic and is not classified as a dangerous goods in transport regulations. :
To avoid a potentially vigorous chemical reaction, barium metal is kept in an argon atmosphere or under mineral oils. Contact with air is dangerous and may cause ignition. Moisture, friction, heat, sparks, flames, shocks, static electricity, and exposure to oxidizers and acids should be avoided. Anything that may contact with barium should be electrically grounded. Anyone who works with the metal should wear pre-cleaned non-sparking shoes, flame-resistant rubber clothes, rubber gloves, apron, goggles, and a gas mask. Smoking in the working area is typically forbidden. Thorough washing is required after handling barium.
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin calx "lime", which was obtained from heating limestone.
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. A hydroxide attached to a strongly electropositive center may itself ionize, liberating a hydrogen cation (H+), making the parent compound an acid.
Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to air. Strontium has physical and chemical properties similar to those of its two vertical neighbors in the periodic table, calcium and barium. It occurs naturally mainly in the minerals celestine and strontianite, and is mostly mined from these. While natural strontium is stable, the synthetic 90Sr isotope is radioactive and is one of the most dangerous components of nuclear fallout, as strontium is absorbed by the body in a similar manner to calcium. Natural stable strontium, on the other hand, is not hazardous to health.
In chemistry, a salt is a solid chemical compound consisting of an ionic assembly of cations and anions. Salts are composed of related numbers of cations and anions so that the product is electrically neutral. These component ions can be inorganic, such as chloride (Cl−), or organic, such as acetate ; and can be monatomic, such as fluoride (F−), or polyatomic, such as sulfate.
The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.
Manganese(IV) oxide is the inorganic compound with the formula MnO
2. This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for MnO
2 is for dry-cell batteries, such as the alkaline battery and the zinc-carbon battery. MnO
2 is also used as a pigment and as a precursor to other manganese compounds, such as KMnO
4. It is used as a reagent in organic synthesis, for example, for the oxidation of allylic alcohols. MnO
2 in the α polymorph can incorporate a variety of atoms in the "tunnels" or "channels" between the manganese oxide octahedra. There is considerable interest in α-MnO
2 as a possible cathode for lithium ion batteries.
Barium hydroxide is a chemical compound with the chemical formula Ba(OH)2(H2O)x. The monohydrate (x =1), known as baryta or baryta-water, is one of the principal compounds of barium. This white granular monohydrate is the usual commercial form.
Barium carbonate (BaCO3), also known as witherite, is a chemical compound used in rat poison, bricks, ceramic glazes and cement.
Barium chloride is the inorganic compound with the formula BaCl2. It is one of the most common water-soluble salts of barium. Like most other barium salts, it is white, toxic, and imparts a yellow-green coloration to a flame. It is also hygroscopic, converting first to the dihydrate BaCl2(H2O)2. It has limited use in the laboratory and industry.
Barium nitrate is the inorganic compound with the chemical formula Ba(NO3)2. It, like most barium salts, is colorless, toxic, and water-soluble. It burns with a green flame and is an oxidizer; the compound is commonly used in pyrotechnics.
Gadolinium(III) oxide (archaically gadolinia) is an inorganic compound with the formula Gd2O3. It is one of the most commonly available forms of the rare-earth element gadolinium, derivatives of which are potential contrast agents for magnetic resonance imaging.
Barium chromate, named barium tetraoxochromate(VI) by the IUPAC, is a yellow sand like powder with the formula BaCrO4. It is a known oxidizing agent and produces a green flame when heated, a result of the barium ions.
Barium peroxide is the inorganic compound with the formula BaO2. This white solid (gray when impure) is one of the most common inorganic peroxides, and it was the first peroxide compound discovered. Being an oxidizer and giving a vivid green colour upon ignition (as do all barium compounds), it finds some use in fireworks; historically, it was also used as a precursor for hydrogen peroxide.
Strontium carbonate (SrCO3) is the carbonate salt of strontium that has the appearance of a white or grey powder. It occurs in nature as the mineral strontianite.
Strontium sulfate (SrSO4) is the sulfate salt of strontium. It is a white crystalline powder and occurs in nature as the mineral celestine. It is poorly soluble in water to the extent of 1 part in 8,800. It is more soluble in dilute HCl and nitric acid and appreciably soluble in alkali chloride solutions (e.g. sodium chloride).
Barium chlorate, Ba(ClO3)2, is a white crystalline solid, the barium salt of chloric acid. It is an irritant and toxic, as are all soluble barium compounds. It is sometimes used in pyrotechnics to produce a green color. It also finds use in the production of chloric acid.
Barium ferrate is the chemical compound of formula BaFeO4. This is a rare compound containing iron in the +6 oxidation state. The ferrate(VI) ion has two unpaired electrons, making it paramagnetic. It is isostructural with BaSO4, and contains the tetrahedral [FeO4]2− anion.
Barium perchlorate is a powerful oxidizing agent, with the formula Ba(ClO4)2. It is used in the pyrotechnic industry.