Boron (B) — Atomic Number 5

Boron is a chemical element with the symbol B and atomic number 5. It is a metalloid — dark, hard, and lustrous. Its name comes from borax, the mineral from which it was first isolated.

At a Glance

Discovery

First isolated in 1808 by French chemists Gay-Lussac and Thénard, and independently by Sir Humphry Davy.

Chemical Properties

Boron has 3 valence electrons and typically forms 3 covalent bonds. It is chemically inert at room temperature.

Key Reactions

1. $4\text{B}+3{\text{O}}_2\to 2{\text{B}}_2{\text{O}}_3$ (at ~700 °C)
2. $2\text{B}+3{\text{Cl}}_2\to 2{\text{BCl}}_3$
3. ${\text{B}}_2{\text{O}}_3+3{\text{H}}_2\text{O}\to 2{\text{H}}_3{\text{BO}}_3$ (boric acid — acidic oxide)

Compounds & Uses

IGCSE Tips

• Metalloid — properties between metals and non-metals
• 3 valence electrons — forms 3 covalent bonds
• Oxide (B₂O₃) is acidic — unusual for a metal-ish element

Sources

• Boron — Wikipedia
• Boron — Ptable.com