Why carbon builds everything
Cooking gas and candle wax are both built on carbon chains.
Add carbons one at a time. Count the slots left for hydrogen.
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The rule
A carbon has four bond slots. In a hydrocarbon, the slots go to hydrogens or to other carbons. Hydrogens fill whatever slots are left open.
Four bond slots is carbon's tetravalency. Carbon bonding to carbon is catenation. Carbon does this very well, so its chains can be long.
| Shape | How the slots go |
|---|---|
| Chain | Each middle carbon spends two slots on carbon neighbours. |
| Branch | One carbon spends three slots on carbon neighbours. |
| Ring | The two ends of a chain join, so each carbon has two hydrogens. |
Four carbons in a chain carry 4 × 4 = 16 slots. A link is one bond between two carbons. It takes one slot from each carbon, so 2 slots. Three links use 3 × 2 = 6 slots. That leaves 16 − 6 = 10 slots for hydrogen. That is C₄H₁₀, butane.
Join six carbons into a ring. They carry 6 × 4 = 24 slots. A ring has 6 links, using 6 × 2 = 12 slots. That leaves 24 − 12 = 12 hydrogens: C₆H₁₂, cyclohexane.