Barium (Ba)

Barium compounds are toxic, but barium sulfate is so insoluble that a patient can drink half a litre of it for an X-ray and absorb essentially none — the difference between a poison and a medicine is entirely a matter of which counter-ion it is paired with. Around three-quarters of world barite production goes into drilling mud, where its density holds back the pressure of the well. Barium was the tell-tale in the discovery of nuclear fission: Otto Hahn found it in uranium bombarded with neutrons in 1938, could not explain how a heavy element had produced a much lighter one, and Lise Meitner worked out that the nucleus had split.

Properties

Atomic number

56

Symbol

Ba

Standard atomic weight

137.33 u

Category

Alkaline earth metal

Group

2

Period

6

Block

s-block

Electron configuration

[Xe] 6s²

Electrons per shell

2, 8, 18, 18, 8, 2

Melting point

1,000 K — 726.9 °C — 1340.3 °F

Boiling point

2,170 K — 1896.8 °C — 3446.3 °F

Density

3.62 g/cm³

Electronegativity

0.89 (Pauling)

Oxidation states

+2

Discovered

1808 by Humphry Davy

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s²

Noble gas shorthand

[Xe] 6s²

Shells

K: 2 · L: 8 · M: 18 · N: 18 · O: 8 · P: 2

What it is used for

• Barium sulfate as the swallowed contrast agent for gut X-rays
• Weighting agent in oil and gas drilling mud
• Green fireworks
• YBCO high-temperature superconductors
• Getters that absorb stray gas inside vacuum tubes

Hazards

• Soluble barium salts are acutely toxic, causing muscle paralysis and cardiac arrhythmia
• Barium metal ignites in air and reacts with water

Neighbours in the table

Group 2

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Barium sits in group 2 with beryllium, magnesium, calcium, strontium, radium.