Element 56 · Alkaline earth metal
Barium (Ba) — Element 56
Greek barys — heavy
Barium (Ba) is an alkaline earth metal in Period 6, Group 2 of the periodic table with atomic number 56, standard atomic weight 137.33 u, and ground-state electron configuration [Xe] 6s². At standard temperature and pressure it is classified as a solid with 2 valence electrons and common oxidation states +2.
X-ray contrast, fireworks (green)
What are the atomic properties and physical constants of Barium?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 56
- Standard atomic mass
- 137.33 u
- Chemical family
- Alkaline earth metal
- Ground-state configuration
- [Xe] 6s²
- Electrons per shell
- 2, 8, 18, 18, 8, 2
- Valence electrons
- 2
- Common ion charges / oxidation states
- +2
- Phase at STP
- Solid
- Pauling electronegativity
- 0.89 Pauling
- First ionization energy
- 503 kJ/mol
- Atomic radius
- 253 pm
- Melting point
- 727 °C
- Boiling point
- 1,897 °C
- Discovery year
- 1808
- Table coordinate
- Period 6, Group 2
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Barium’s shells?
A neutral Barium atom contains 56 electrons distributed across 6 occupied principal energy shells ([Xe] 6s²). The table below compares Barium’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in Ba | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 18 e⁻ | 18 e⁻ |
| n = 4 | N | 18 e⁻ | 32 e⁻ |
| n = 5 | O | 8 e⁻ | 50 e⁻ |
| n = 6 | P | 2 e⁻ | 72 e⁻ |
Frequently Asked Questions about Barium (Ba)
What is the atomic mass and atomic number of Barium (Ba)?
Barium (Ba) has atomic number Z = 56 (56 protons in its nucleus) and an IUPAC standard atomic weight of 137.33 u. It sits in Period 6, Group 2 and is classified as an alkaline earth metal.
What is the ground-state electron configuration of Barium?
The neutral ground-state electron configuration of Barium (Z = 56) is [Xe] 6s². Across its 6 occupied principal shells (n = 1 to n = 6), the electrons per shell are 2, 8, 18, 18, 8, 2, with 2 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Barium?
Barium commonly forms +2 oxidation states or ion charges in compounds. Its Pauling electronegativity is 0.89 and its first ionization energy is 503 kJ/mol.
When was Barium discovered and what is it used for?
Barium was discovered in 1808 (Greek barys — heavy). X-ray contrast, fireworks (green)
How does Barium compare to neighboring elements?
Other alkaline earth metal elements: