Organic chemistry

Methane, ethylene, acetylene, benzene

Compare saturated methane, double- and triple-bonded hydrocarbons, and aromatic benzene.

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IntuitionIntuition: carbon frameworks

Carbon shares electrons to bond. It forms methane with hydrogen; carbon atoms link by single, double or triple bonds. Benzene is a special six-carbon ring.

Compare methane, ethene, ethyne and benzene.

SchoolSchool level: formulas and reactions

Definition: Hydrocarbon

C–C single, double and triple bonds share one, two and three electron pairs.

Complete combustion:

\ce{CH4 + 2O2 -> CO2 + 2H2O}

Addition:

\ce{C2H4 + H2 -> C2H6}

;

\ce{C2H2 + 2H2 -> C2H6}

Four hydrocarbons
Name	Formula
Methane	CH4
Ethylene / ethene	C2H4
Acetylene / ethyne	C2H2
Benzene	C6H6

Example: Combustion balance

Solution

2 C form 2 CO2; 4 H form 2 H2O; then 3 O2 balance oxygen: $\ce{C2H4 + 3O2 -> 2CO2 + 2H2O}$ .

SchoolHistory: benzene structure

UndergraduateUniversity extension: aromaticity

Benzene’s delocalized π electrons make its six C–C bonds equivalent. Its aromatic stabilization means it usually undergoes substitution rather than addition that destroys the ring.

Methane is a fuel; ethylene is a plant-ripening signal and industrial feedstock; acetylene is used in oxy-acetylene welding.

Limited oxygen can cause incomplete combustion, producing poisonous carbon monoxide or soot.

Benzene is toxic and carcinogenic; it is not a safe classroom solvent.