Carbon (C) — Atomic Number 6

Carbon is a chemical element with the symbol C and atomic number 6. It is the foundation of organic chemistry — the chemical basis of all known life. Its name comes from Latin carbo meaning “coal.” Carbon atoms can bond together in chains, rings, and networks — giving rise to millions of compounds.

At a Glance

Allotropes — The Many Forms of Carbon

Diamond

• Giant covalent structure — each C bonded to 4 others tetrahedrally
• Hardest natural substance — used in cutting and jewellery
• Does not conduct electricity (all electrons in covalent bonds)

Graphite

• Giant covalent layered structure — each C bonded to 3 others in hexagonal sheets
• Soft and slippery — layers slide over each other (weak forces between layers)
• Conducts electricity — one delocalised electron per carbon between layers
• Uses: pencils, electrodes, lubricants

Chemical Properties

1. Complete combustion: $\text{C}+{\text{O}}_2\to {\text{CO}}_2$
2. Incomplete combustion: $2\text{C}+{\text{O}}_2\to 2\text{CO}$ (carbon monoxide — toxic)
3. Reducing agent: $2{\text{Fe}}_2{\text{O}}_3+3\text{C}\to 4\text{Fe}+3{\text{CO}}_2$ (blast furnace)

Test for CO₂

Bubble through limewater → turns milky/cloudy: ${\text{Ca(OH)}}_2+{\text{CO}}_2\to {\text{CaCO}}_3+{\text{H}}_2\text{O}$

Compounds

Biological Role

Carbon is the defining element of life — all organic molecules (carbohydrates, proteins, lipids, DNA) are carbon-based. The carbon cycle moves carbon through atmosphere, biosphere, and lithosphere.

IGCSE Essentials

1. 4 valence electrons — forms 4 covalent bonds
2. Allotropes: Diamond (hard, insulator) vs Graphite (soft, conductor)
3. Test for CO₂: limewater turns milky
4. Used as a reducing agent in metal extraction

Sources

• Carbon — Wikipedia
• Carbon — Ptable.com
• Carbon — RSC Periodic Table