Carbon and its Compounds
What is tested
This domain covers covalent bonding, allotropes, homologous series, functional groups, isomerism, reactions of carbon compounds, ethanol, ethanoic acid, soaps and detergents. Questions often ask you to identify a functional group or complete an equation.
Core rules
- Carbon is tetravalent and forms strong covalent bonds. It shows catenation, forming chains and rings.
- Diamond, graphite and fullerene are allotropes of carbon. Diamond is hard and non-conducting; graphite is soft and conducts because of delocalised electrons.
- A homologous series has the same functional group and successive members differ by CH2, that is 14 u.
- Saturated compounds mainly show substitution; unsaturated compounds show addition. Combustion and oxidation are also important reactions.
- Functional groups include alcohol -OH, carboxylic acid -COOH, aldehyde -CHO, ketone -CO- and halide -X.
- Soap molecules form micelles and clean in soft water; detergents work even in hard water.
Worked example
Ethene is unsaturated and adds hydrogen in the presence of nickel: C2H4 + H2 → C2H6. Ethene has a double bond; ethane has only single bonds. This is an addition reaction, not substitution.
Traps
Isomers have the same molecular formula but different structures. Do not say graphite and diamond have different elements. Ethanoic acid is called glacial acetic acid when pure and frozen. Soap is less effective in hard water because calcium and magnesium ions form scum.