Recognised as Chemical element
Barium
- Ba
- Z = 56
- alkaline earth metal
Barium (Ba) is element 56, an alkaline earth metal in period 6 and group 2. Its standard atomic weight is 137.33 Da. Weights follow IUPAC standard atomic weights, 2021 revision.
Identity
SymbolBa
Standard atomic weight137.33atomic mass units (Da)
Mass in kilograms2.2804183 × 10^-25
Categoryalkaline earth metal
Group2
Period6
Blocks-block
Electrons in a neutral atom56
Neutrons in the most common isotope81≈
Electron configuration
Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s²ground state, subshells written in order of n
Noble gas shorthand[Xe] 6s²
Electrons per shell2, 8, 18, 18, 8, 2K, L, M and outward
Electrons in the outer shell2
Unpaired electrons0Hund's rule; none unpaired, so the free atom is diamagnetic
Madelung ruleFollowedthe ground state is what the n + l filling order predicts
Quantities
Molar mass137.33 g/mol
Mass of one mole137.33 grams
Atoms in one gram4.3851604 × 10^21
Mass of one atom2.2804183 × 10^-22 g
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