005Metalloid · Group 13 · Period 2
Boron
Boron (B) is element 5, a metalloid in the p-block — group 13, period 2. It is a solid at room temperature with 2 electron shells (2, 3) and an atomic mass of 10.81 u.
- Atomic mass
- 10.81 u
- Phase · STP
- solid
- Melting
- 2349 K · 2076 °C
- Boiling
- 4200 K · 3927 °C
- Electronegativity
- 2.04
- Density
- 2.08 g/cm³
Photograph — Jurii, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons, source: https://images-of-elements.com/boron.php
Identity
- Atomic number
- 5
- Standard atomic weight
- 10.81 u
- Category
- Metalloid
- Group
- 13
- Period
- 2
- Block
- p-block
- Oxidation states
- +3
Physical properties
- Melting point
- 2349 K · 2076 °C
- Boiling point
- 4200 K · 3927 °C
- Density
- 2.08 g/cm³
- Molar heat capacity
- 11.087 J/(mol·K)
- Atomic radius
- 192 pm
- Electron affinity
- 26.989 kJ/mol
Atomic structure
5protons
6neutrons
5electrons
3valence e⁻
- Noble-gas notation
- [He] 2s2 2p1
- Full configuration
- 1s2 2s2 2p1
- Electrons per shell
- 2, 3
Periodic trends
Where Boron ranks across all 118 elements.
Ionization energies
Energy to remove each successive electron (kJ/mol).
800.61
2.4k2
3.7k3
25.0k4
32.8k5
Successive ionization energies (kJ/mol, log scale).
Discovery
- Discovered
- 1808
- Discovered by
- Joseph Louis Gay-Lussac
- Named by
- —
- Appearance
- black-brown