Barium (Ba)
Element 56 · Alkaline earth metal · atomic mass 137.33 u · group 2, period 6
Electron shells: 2, 8, 18, 18, 8, 2
Barium compounds are dense and opaque to X-rays, which is why patients drink barium sulfate before a scan. Soluble barium salts, by contrast, are seriously toxic.
The "barium meal" is safe only because barium sulfate refuses to dissolve — soluble barium salts are poisons.
- Atomic number
- 56
- Atomic mass
- 137.33 u
- Electron configuration
- [Xe] 6s²
- Group · period · block
- 2 · 6 · s
- Oxidation states
- +2
- Electronegativity
- 0.89 (Pauling)
- Melting point
- 727 °C
- Boiling point
- 1,897 °C
- Density
- 3.62 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery-white metal
- Discovered
- Carl Wilhelm Scheele; isolated by Humphry Davy, 1808
56 protons, and 56 electrons when neutral
IUPAC standard atomic weight
Alkaline earth metals
What Barium is used for
- Barium meal X-ray contrast
- Oil-drilling mud weighting
- Green fireworks
- Vacuum tube getters
Atomic structure of Barium
A neutral barium atom has 56 protons and 56 electrons. Its most common isotope carries about 81 neutrons, which is where the mass number 137 comes from. Change the neutron count and you have a different isotope of barium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 18, 8, 2. In orbital notation that is [Xe] 6s², leaving 2 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Barium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Barium sits in the periodic table
Group 2 metals with two outer electrons. Harder and less reactive than the alkali metals, and they form the +2 ions that build bone, shell and cement.
Discovery and naming
Barium was discovered by Carl Wilhelm Scheele; isolated by Humphry Davy in 1808. Its name comes from Greek barys, "heavy".
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Barium?
The standard atomic weight of Barium is 137.33 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Barium have?
Barium has 56 protons, because the atomic number is the proton count and that is what makes an atom Barium at all. A neutral Barium atom has the same number of electrons, 56. The neutron count varies by isotope; the most common one has about 81, since 137 − 56 = 81.
What is the electron configuration of Barium?
The electron configuration of Barium is [Xe] 6s². Its electrons are arranged 2, 8, 18, 18, 8, 2 across 6 shells.
Is Barium a metal?
Yes. Barium is classified as a alkaline earth metal, on the left side of the table.
What group and period is Barium in?
Barium is in group 2 (the alkaline earth metals), period 6, in the s-block. The group is its column and the period is its row.
What is the charge of Barium?
Barium most commonly forms a 2+ ion. It has 2 electrons in its outer shell and loses them readily, which is what the group number tells you.
What is the melting point of Barium?
Barium melts at 727 °C and boils at 1,897 °C. That puts it in the solids at everyday temperatures.
What is Barium used for?
Barium meal X-ray contrast, Oil-drilling mud weighting, Green fireworks, Vacuum tube getters. Barium compounds are dense and opaque to X-rays, which is why patients drink barium sulfate before a scan.
Who discovered Barium, and where does its name come from?
Barium (Ba) was discovered by Carl Wilhelm Scheele; isolated by Humphry Davy in 1808. The name comes from Greek barys, "heavy".