Boron
Element 5 · Metalloid
Boron sits on the staircase boundary between metals and nonmetals, and it behaves like a true in-between: hard and brittle like a ceramic, yet able to tune the conductivity of silicon in computer chips. It never appears free in nature; instead it forms borate minerals such as borax. Humans have used it for millennia in glazes and glass, and modern chemistry relies on boron compounds for heat-resistant borosilicate labware, detergents, fiberglass insulation, and the control rods that tame nuclear reactors. Plants need boron in tiny amounts to build cell walls.
Key facts
| Atomic number | 5 |
|---|---|
| Atomic weight | 10.81 |
| Category | Metalloid |
| Group / Period | 13 / 2 |
| Block | p |
| Electron configuration | 1s2 2s2 2p1 |
| Common oxidation states | +3 |
| State at STP | Solid |
| Electronegativity | 2.04 |
| Atomic radius | 87 pm |
| Density | 2.34 g/cm³ |
| Melting point | 2075 °C |
| Boiling point | 4000 °C |
Occurrence
Boron concentrates in evaporite deposits left by ancient lakes and seas. Major borate mines operate in Turkey and the United States. It reaches plants through soil water in trace amounts.
Applications
Borosilicate heat-resistant glass
Detergents and cleaning borax
Fiberglass insulation
Semiconductor doping
Neutron-absorbing control rods
Common compounds
- Borax (Na2B4O7·10H2O)
- Boric acid (H3BO3)
- Boron carbide (B4C)
- Boron nitride (BN)
Boron carbide ranks among the hardest materials known — it armors military vehicles and stops bullets in ceramic body armor.
Data source: IUPAC standard atomic weights 2021