Boron
metalloidProperties
| Property | Value |
|---|---|
| Atomic Mass | 10.81 amu |
| Category | metalloid |
| Group | 13 |
| Period | 2 |
| Electron Configuration | 1s2 2s2 2p1 |
| Electronegativity | 2.04 (Pauling) |
| Oxidation States | 3 |
| Melting Point | 2349 K (2075.8 °C) |
| Boiling Point | 4200 K (3926.8 °C) |
| Density | 2.34 g/cm³ |
| Discovered By | Joseph Louis Gay-Lussac (1808) |
About Boron
Boron is the element that broke valence theory. With only three valence electrons and an empty 2p orbital, it cannot satisfy the octet rule the easy way, so it invented its own bonding: three-center two-electron bonds, the famous "banana bonds" of diborane (B₂H₆) that William Lipscomb spent a Nobel-winning career mapping out. The boranes and carboranes that grew out of that work are cage molecules — icosahedra of boron with hydrogens hanging off — and they remain a playground for inorganic chemists looking for unusual coordination geometries. On the practical side, boron oxide is the network former that turns ordinary soda-lime glass into Pyrex, knocking the thermal expansion coefficient down by a factor of three so a beaker survives a 200 °C temperature shock. The same ¹⁰B isotope that absorbs thermal neutrons aggressively (cross-section 3837 barns) shows up in PWR control rods, in BNCT cancer therapy, and as the boron-doped polysilicon counter in every neutron-monitoring station built since 1980.
Fun Fact
Cubic boron nitride is the second-hardest known material after diamond, and unlike diamond it does not react with iron at red heat — which is why machinists grind hardened steel with cBN wheels and not with diamond.
Common Uses
- Borosilicate glass (Pyrex, lab glassware) for low thermal expansion
- Fiberglass insulation and reinforcement for buildings
- B-10 enriched control rods and emergency boron injection in PWRs
- NdFeB rare-earth magnets for EV motors and hard drives
- Borax and perborate bleach activators in detergents