Barium

Barium: the essentials

Barium is a metallic element, soft, and when pure is silvery white like lead. The metal oxidises very easily and it reacts with water or alcohol. Barium is one of the alkaline-earth metals. Small amounts of barium compounds are used in paints and glasses.

The result of adding different metal salts to a burning reaction mixture of potassium chlorate and sucrose. The red colour originates from strontium sulphate. The orange/yellow colour originates from sodium chloride. The green colour originates from barium chlorate and the blue colour originates from copper (I) chloride. The lilac colour that should be evident from the potassium chlorate is washed out by the other colours, all of which are more intense (only to be demonstrated by a professionally qualified chemist following a legally satisfactory hazard asessment). Improperly done, this reaction is dangerous!

Barium salts impart green colours to flames. The picture above shows the colour arising from adding barium chlorate (BaClO₃) to a burning mixture. Do not attempt this reaction unless are a professionally qualified chemist and you have carried out a legally satisfactory hazard assessment.

Barium: historical information

Baryta (barium oxide, BaO) was distinguished from lime (calcium oxide, CaO) by Scheele in 1774. Elemental barium was isolated by Sir Humphrey Davy in 1808 who electrolysed molten baryta.

Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for barium is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]

Barium: physical properties

• Melting point: 1000 [or 727 °C (1341 °F)] K
• Boiling point: 2143 [or 1870 °C (3398 °F)] K
• Density of solid: 3510 kg m^-3

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Barium: orbital properties

• Ground state electron configuration:  [Xe].6s²
• Shell structure:  2.8.18.18.8.2
• Term symbol:   ¹S₀
• Pauling electronegativity: 0.89 (Pauling units)
•  First ionisation energy: 502.9 kJ mol^-1
•  Second ionisation energy: 965.2 kJ mol^-1

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Isolation

Isolation: barium metal is available commercially and there is normally no need to make it in the laboratory. Commercially, it is made on small scale by the electrolysis of molten barium chloride, BaCl₂.

cathode: Ba²⁺(l) + 2e^- → Ba

anode: Cl^-(l) → ¹/₂Cl₂ (g) + e^-

Barium metal can also be islated from the reduction of barium oxide, BaO, with aluminium.

6BaO + 2Al→ 3Ba + Ba₃Al₂O₆

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