The many compounds of carbon

Carbon makes millions of compounds, for two reasons:

• Tetravalency: each carbon has four bonds to make. Think of four seats that must always be filled.
• Catenation: carbon can bond to other carbons, in long chains, branched chains and rings.

Drawing a structure: join the carbons first, give each one four bonds, and fill the empty seats with hydrogen. If there aren't enough hydrogens to fill every seat, put a double (or triple) bond between two carbons.

Compounds of only carbon and hydrogen are hydrocarbons:

Unsaturated compounds are more reactive.

Isomers: butane, C₄H₁₀, can be drawn as a straight chain or as a branched chain. Same formula, different structures: these are structural isomers. Careful: moving a branch to the other end of the chain gives the same molecule, not a new one.

Swap a hydrogen for another atom or group and the compound behaves differently. That group is the functional group: it decides the chemical properties.

A homologous series is a family with the same functional group, where each member has one more –CH₂– (14 u) than the one before: methanol, ethanol, propanol, butanol. Their chemical properties are alike; their boiling points rise as the molecules get bigger.

Naming: count the carbons for the stem (1 meth-, 2 eth-, 3 prop-, 4 but-), then add the functional group's ending. Three carbons with a ketone group: propanone. Why is there no "methanone"? A ketone group needs a carbon on each side of it, so it needs at least three carbons.