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. 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. 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. 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. 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 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 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. 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).