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Barium

Element 56 · Alkaline earth metal

Specimen

Atomic number
56
Atomic mass
137.33
State at room temperature
Solid
Melting point
726.9 °C
Boiling point
1,897 °C
Density
3.62 g/cm³
Discovered
1808

Atomic mass from IUPAC.1 Other physical data from PubChem.2

Can I eat it?

In food and water
Harmful. Barium salts that dissolve can cause vomiting, muscle weakness and changes in heart rhythm. Barium sulfate does not dissolve well and is not generally harmful. The US EPA limits barium in drinking water to 2 mg per liter. 3

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The atom

Ba
ShellElectrons
1 (K) 2
2 (L) 8
3 (M) 18
4 (N) 18
5 (O) 8
6 (P) outermost 2
Total56

Configuration [Xe] 6s²

6s ↑ ↓
A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 56 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the Xe core, with one arrow per electron.

Related elements

Group 2
Be Beryllium Mg Magnesium Ca Calcium Sr Strontium Ra Radium

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Sources

  1. 1

    IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024. Abridged Standard Atomic Weights 2024 .

    The atomic mass shown for the 84 elements that have a standard atomic weight.

  2. 2

    National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

    Electron configuration, melting and boiling points, density and discovery year for all 118 elements.

  3. 3

    Agency for Toxic Substances and Disease Registry (ATSDR), 2007. ToxFAQs for Barium .

    • Barium compounds that do not dissolve well, such as barium sulfate, are not generally harmful.
    • may experience vomiting, abdominal cramps, diarrhea ... and muscle weakness ... amounts of barium compounds that easily dissolve can cause changes in heart rhythm or paralysis and possibly death.
    • The EPA has set a limit of 2.0 milligrams of barium per liter of drinking water (2.0 mg/L)
  4. 4

    National Institute of Standards and Technology (NIST), 2026. Atomic Weights and Isotopic Compositions for All Elements .

    Isotopic composition of each element; the most abundant isotope sets the neutron count in the nucleus view.