ElementsWhat is barium?
Barium is a soft, silvery metal that reacts with air and water. Its salts give a green colour to flames.
What is barium used for?
Barium sulfate for X-ray pictures of the stomach, drilling muds, green fireworks, and glass.
Where the name comes from
From the Greek word barys, heavy.
Key facts
- Symbol
- Ba
- Atomic number
- 56
- Atomic mass
- 137.33 u
- Family
- Alkaline earth metal
- Period
- 6
- Group
- 2
- Block
- s
- State at room temperature
- Solid
- Melting point
- 726.9 °C (1,000 K, 1,340 °F)
- Boiling point
- 1,897 °C (2,170 K, 3,446 °F)
- Density
- 3.62 g/cm³
- Electrons per shell
- 2, 8, 18, 18, 8, 2
- Electron configuration
- [Xe]6s2
- Common oxidation states
- +2
- Electronegativity (Pauling)
- 0.89
- First ionisation energy
- 5.212 eV
- Electron affinity
- no value
- Atomic radius (van der Waals)
- 268 pm
- Discovered
- 1808
Place in the periodic table
Barium is element number 56. It sits in period 6 (row 6) of the periodic table, in group 2 (column 2), and belongs to the s-block. Just before it comes caesium (55), and just after it comes lanthanum (57). In the same column, strontium is above it and radium is below it. Elements in one column tend to behave alike.
Family: Alkaline earth metals.
Physical properties
At room temperature barium is a solid. It melts at 726.9 °C and boils at 1,897 °C, so it stays liquid over a range of 1,170 degrees. Its density is 3.62 grams per cubic centimetre, so a one-litre block would weigh about 3.62 kilograms. By density it ranks 68th among the 96 elements with a measured value.
Inside the atom
An atom of barium has 56 protons in its nucleus and, when neutral, 56 electrons around it. The electrons are arranged in 6 shells: 2, 8, 18, 18, 8, 2. The outermost shell holds 2 electrons. Written in full, the electron configuration is [Xe]6s2.
Its electronegativity on the Pauling scale is 0.89. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 5.212 electronvolts (about 503 kilojoules per mole). One mole of barium weighs 137.33 grams, so a single gram contains about 4.39 × 1021 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains barium with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.