About

Barium is a soft, silvery alkaline earth metal that is chemically similar to calcium. Due to its high density, the compound barium sulfate is opaque to X-rays and is ingested by patients as a 'barium meal' to provide clear imaging of the gastrointestinal tract in medicine. It also gives a characteristic pale green color to fireworks and is used as a 'getter' to remove residual gas from vacuum tubes.

Atomic Properties

Atomic Number56

Atomic Weight137.327 u

Neutrons (common)82

Electron Configuration[Xe] 6s²

Full Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s²

Electrons per Shell2, 8, 18, 18, 8, 2

Electronegativity0.89

Electron Affinity13.954 kJ/mol

Oxidation States+2

Covalent Radius215 pm

Van der Waals Radius268 pm

Ionic Radius135 pm

Periodic Table Position

Group2

Period6

BlockS

Chemical SeriesAlkaline earth metals

Physical Properties

State at STPsolid

Appearancesilvery-white metallic

Crystal Structurebcc

Magnetic Orderingparamagnetic

Speed of Sound1,620 m/s

Poisson Ratio0.28

Thermal Properties

Melting Point1,000 K

Boiling Point2,170 K

Triple Point1,000 K

Thermal Expansion0 1/K

Thermal Conductivity18.4 W/(m·K)

Specific Heat0.204 J/(g·K)

Molar Heat28.07 J/(mol·K)

Heat of Fusion7.12 kJ/mol

Heat of Vaporization142 kJ/mol

Abundance

In Earth's Crust425 ppm

In Ocean0.006 ppm

In Solar System0.002 ppm

In Human Body0.031 ppm

In Universe0.01 ppm

Discovery

Discovered byHumphry Davy

Discovery Year1,808

Occurrenceprimordial

CAS Number7440-39-3

Electron Configuration

Energy

↿⇂

Isotopes of Barium

Symbol ▲	Mass (u) ▲	Abundance ▲	Half-life ▲	Decay Mode ▲
¹³⁰Ba	129.906320	0.106%	Stable	Stable
¹³²Ba	131.905060	0.101%	Stable	Stable
¹³⁴Ba	133.904510	2.417%	Stable	Stable
¹³⁵Ba	134.905690	6.592%	Stable	Stable
¹³⁶Ba	135.904580	7.854%	Stable	Stable
¹³⁷Ba	136.905830	11.232%	Stable	Stable
¹³⁸Ba	137.905250	71.698%	Stable	Stable

Interactive Visualization

Explore the 3D Bohr model of Barium in our interactive viewer.

View 3D Model of Barium