Element 5 · Metalloid
Boron (B) — Element 5
Arabic buraq — borax
Boron (B) is a metalloid in Period 2, Group 13 of the periodic table with atomic number 5, standard atomic weight 10.81 u, and ground-state electron configuration [He] 2s² 2p¹. At standard temperature and pressure it is classified as a solid with 3 valence electrons and common oxidation states +3.
Glass, detergents, semiconductors
What are the atomic properties and physical constants of Boron?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 5
- Standard atomic mass
- 10.81 u
- Chemical family
- Metalloid
- Ground-state configuration
- [He] 2s² 2p¹
- Electrons per shell
- 2, 3
- Valence electrons
- 3
- Common ion charges / oxidation states
- +3
- Phase at STP
- Solid
- Pauling electronegativity
- 2.04 Pauling
- First ionization energy
- 801 kJ/mol
- Atomic radius
- 87 pm
- Melting point
- 2,076 °C
- Boiling point
- 3,927 °C
- Discovery year
- 1808
- Table coordinate
- Period 2, Group 13
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Boron’s shells?
A neutral Boron atom contains 5 electrons distributed across 2 occupied principal energy shells ([He] 2s² 2p¹). The table below compares Boron’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in B | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 3 e⁻ | 8 e⁻ |
Frequently Asked Questions about Boron (B)
What is the atomic mass and atomic number of Boron (B)?
Boron (B) has atomic number Z = 5 (5 protons in its nucleus) and an IUPAC standard atomic weight of 10.81 u. It sits in Period 2, Group 13 and is classified as a metalloid.
What is the ground-state electron configuration of Boron?
The neutral ground-state electron configuration of Boron (Z = 5) is [He] 2s² 2p¹. Across its 2 occupied principal shells (n = 1 to n = 2), the electrons per shell are 2, 3, with 3 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Boron?
Boron commonly forms +3 oxidation states or ion charges in compounds. Its Pauling electronegativity is 2.04 and its first ionization energy is 801 kJ/mol.
When was Boron discovered and what is it used for?
Boron was discovered in 1808 (Arabic buraq — borax). Glass, detergents, semiconductors
How does Boron compare to neighboring elements?
Other metalloid elements: