Barium is a soft, silvery alkaline-earth metal. It oxidizes rapidly in air and reacts with water to produce hydrogen gas and barium hydroxide. It is used in vacuum tubes, getters, and as barium sulfate in radiology.
Barium has the ground-state configuration [Xe] 6s2. Like other Group 2 metals, it readily loses two electrons to form Ba2+, which explains its strong reducing character and vigorous reactions with water and oxygen.
Barium reacts rapidly with water to form barium hydroxide and hydrogen gas; the heat of reaction can be significant:
\(\mathrm{Ba(s) + 2\,H_2O(l) \rightarrow Ba(OH)_2(aq) + H_2(g)}\)
In air, Ba forms oxides and peroxides:
\(\mathrm{2\,Ba(s) + O_2(g) \rightarrow 2\,BaO(s)}\)
\(\mathrm{Ba(s) + O_2(g) \rightarrow BaO_2(s)}\)
BaSO4 is extremely insoluble in water and body fluids, so it does not release toxic Ba2+ ions under normal conditions. Its high atomic number provides strong X-ray attenuation, making the gastrointestinal tract visible in imaging.
Soluble barium salts (e.g., BaCl2, Ba(NO3)2) are toxic because free Ba2+ interferes with potassium channels and muscle function. BaSO4 is considered safe for medical imaging due to its negligible solubility.
Barium primarily exhibits the +2 oxidation state. Key compounds include:
Barium is typically produced from barite (BaSO4) by carbothermal reduction to barium sulfide, then conversion to other salts:
\(\mathrm{BaSO_4(s) + 4\,C(s) \rightarrow BaS(s) + 4\,CO(g)}\)
BaS is then treated (e.g., with H2SO4 or CO2) to make BaSO4 or BaCO3, or further processed to other Ba compounds.
Barium imparts a apple-green color to a flame. This arises from electronic transitions of Ba2+ that emit in the green region of the spectrum when excited thermally.
Because of the intense green flame color and the oxidizing ability of barium nitrate \(\mathrm{Ba(NO_3)_2}\), barium salts are used to produce bright green effects in fireworks. Strict handling is required due to toxicity.
Barium hydroxide is a strong base that dissociates substantially in water, yielding highly basic solutions. A representative neutralization is:
\(\mathrm{Ba(OH)_2(aq) + 2\,HCl(aq) \rightarrow BaCl_2(aq) + 2\,H_2O(l)}\)
BaSO4 forms a dense, insoluble precipitate when Ba2+ meets sulfate; this underpins gravimetric analysis of sulfate:
\(\mathrm{Ba^{2+}(aq) + SO_4^{2-}(aq) \rightarrow BaSO_4(s)\downarrow }\)
Its extremely low solubility product makes it ideal for quantitative precipitation.
Fresh barium surfaces chemisorb residual gases (O2, N2, CO, CO2, H2O), improving vacuum quality. In tubes, a Ba film is flashed in situ to scavenge trace gases that would otherwise degrade performance.
Store Ba under dry mineral oil or inert gas to prevent oxidation and contact with moisture. Handle with gloves and eye protection; keep away from water, acids, and oxidizers. Soluble barium wastes must be collected and disposed of as hazardous materials.