Carbon
& its Compounds

Carbon has 4 valence electrons, so instead of gaining or losing four, it shares them — forming covalent bonds. Two superpowers follow: tetravalency (four bonds) and catenation (bonding to other carbons in long chains, branches and rings). Together they explain why there are millions of carbon compounds.

Compounds of only carbon and hydrogen are hydrocarbons. With only single bonds they are saturated (alkanes); with a double or triple bond they are unsaturated (alkenes / alkynes).

A homologous series is a family of compounds with the same general formula and functional group, where each member differs from the next by –CH₂–. Properties change gradually down the series. Build the alkanes:

Try the interactive at the top of the page — build alkanes from methane to hexane, one –CH₂– at a time.

• Combustion: hydrocarbon + O₂ → CO₂ + H₂O + heat (a clean blue flame means complete combustion).
• Oxidation: alcohols can be oxidised to acids (e.g. ethanol → ethanoic acid).
• Addition: unsaturated compounds add H₂ (hydrogenation, Ni catalyst) — oils → fats.
• Substitution: saturated alkanes swap an H for another atom (e.g. with chlorine in sunlight).

Ethanol (C₂H₅OH) — the alcohol in drinks and sanitisers; reacts with sodium to give H₂.

Ethanoic acid (CH₃COOH) — vinegar is its 5–8% solution; a weak acid that turns blue litmus red and reacts with alcohols to form sweet-smelling esters.