56 Ba 137.327

Barium

Alkaline earth metal Barium solid

[Xe] 6s² · 2 · 8 · 18 · 18 · 8 · 2

← Cs Caesium La Lanthanum →

A heavy alkaline earth metal whose name means heavy. Barium sulfate is so insoluble that it is safe to drink before an X-ray, even though every soluble barium salt is a potent poison.

3D model

Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.

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Atomic properties

Atomic number: 56
Atomic mass: 137.327 а.е.м.
Electron configuration: [Xe] 6s²
Electrons per shell: 2 · 8 · 18 · 18 · 8 · 2
Block: s-block
Group: Alkaline earth metals
Period: 6
Electronegativity (Pauling): 0.89
Electronegativity (Allen): 0.88
Atomic radius: 253 pm
Covalent radius: 215 pm
Van der Waals radius: 268 pm
Ionisation energy 1: 502.9 kJ/mol
Ionisation energy 2: 965.2 kJ/mol
Ionisation energy 3: 3 600 kJ/mol
Electron affinity: 13.95 kJ/mol
Common oxidation states: +2
Oxidation states: +1, +2

Physical properties

State at 25 °C: solid
Density: 3.51 g/cm³
Melting point: 1 000 K · 726.9 °C
Boiling point: 2 118 K · 1 844.9 °C
Speed of sound: 1 620 m/s

Thermal properties

Heat of fusion: 7.12 kJ/mol
Heat of vaporisation: 140 kJ/mol
Specific heat capacity: 0.204 J/(g·K)
Thermal conductivity: 18.4 W/(m·K)

Mechanical properties

Young's modulus: 13 GPa
Shear modulus: 4.9 GPa
Bulk modulus: 9.6 GPa
Poisson ratio: no data
Mohs hardness: 1.25
Brinell hardness: no data

Electrical and magnetic properties

Electrical resistivity: 332 nΩ·m
Magnetic ordering: paramagnetic
Curie point: no data
Néel point: no data
Superconducting point: no data

Crystal structure

Crystal structure: body-centred cubic (bcc)
Lattice constants: a = 502.8 pm

Abundance

In the crust: 425 mg/kg
In the ocean: 0.013 mg/L
In the universe: 10 mg/kg
In the human body: 0.3 mg/kg

Isotopes

Isotope	Abundance	Half-life	Decay mode
¹³⁰Ba	0.106 %	stable	—
¹³²Ba	0.101 %	stable	—
¹³⁴Ba	2.417 %	stable	—
¹³⁵Ba	6.592 %	stable	—
¹³⁶Ba	7.854 %	stable	—
¹³⁷Ba	11.232 %	stable	—
¹³⁸Ba	71.698 %	stable	—

Barium-133 serves as a gamma calibration source; barium-137m is the daughter of caesium-137 and powers the teaching generators used to demonstrate radioactive decay.

Discovery

Year of discovery: 1808
Discovered by: Humphry Davy
Where: England
Origin of the name: from Greek barys (heavy): baryte is unusually dense for a stone

History

Baryte was known to alchemists as the Bologna stone: calcined, it glowed in the dark. Scheele recognised a new earth in it in 1772, and Davy isolated the metal in 1808.

Where it occurs

425 mg/kg of the crust — the fourteenth most abundant element. The main minerals are baryte, BaSO₄, and witherite.

How it is produced

Baryte is mostly used as mined, simply ground. Barium metal comes from aluminothermic reduction of the oxide in vacuum.

Role in living things

No biological role. The barium ion blocks potassium channels, which is the basis of its toxicity.

Safety

Soluble barium salts are potent poisons: a lethal dose of the chloride is about a gram. The insoluble sulfate is safe, but confusing one for the other in a hospital has caused mass poisonings.

Uses

Weighting agent in drilling mud — over 80 % of the baryte mined
Barium sulfate contrast suspension for imaging the stomach and bowel
Green colour in pyrotechnics
Getters in vacuum devices: barium mops up residual gas
Ferroelectric ceramics based on barium titanate

Curiosities

The name means heavy: baryte is unusually dense for a non-metallic stone.
The seventeenth-century Bologna stone — calcined baryte — glowed after exposure to light and was taken for a wonder.
The difference between a deadly poison and a safe medicine here is nothing but solubility.
Barium titanate was the first ferroelectric discovered and still underlies most ceramic capacitors.