The vocabulary of this chapter tells one story: carbon builds families called homologous series, each defined by a functional group, and a small set of named reactions moves you from one family to the next along a single reaction map.
The terms in Carbon Compounds are best learned as one connected story rather than a list, because they all describe the same thing from different angles: how carbon builds families of compounds and how those families turn into one another. Once you see how the definitions link up, the chapter stops being a pile of names and becomes a map you can walk across in an answer, and that map is where the marks are, since so many questions here reward the exact word.
Building blocks: series, formulae and structure. Everything begins with the carbon compound, a compound of carbon with other elements, and its most basic type, the hydrocarbon, which contains only carbon and hydrogen. Carbon compounds are grouped into a homologous series, a family that shares one general formula and one functional group, whose members differ by CH₂ and change gradually in physical properties. The functional group is the reactive part that gives each series its chemistry. To describe a single molecule we use its molecular formula, the actual atom count, or its structural formula, which shows how the atoms are joined. Two words separate the two great classes of hydrocarbon: saturated, meaning single carbon–carbon bonds only, and unsaturated, meaning at least one carbon–carbon double bond. This saturated–unsaturated split is the first pair students must keep straight, because it decides which reactions a compound can do.
The families themselves. Five series carry the chapter. The alkane is a saturated hydrocarbon, CₙH₂ₙ₊₂, relatively unreactive. The alkene is unsaturated, CₙH₂ₙ, with a reactive C=C double bond. The alcohol carries the hydroxyl group –OH, the carboxylic acid carries the carboxyl group –COOH and behaves as a weak acid, and the ester carries the –COO– linkage and smells sweet. The alcohol and the acid are the two oxygen-bearing series, and students often confuse them: the neutral –OH of the alcohol is not the acidic –COOH of the carboxylic acid, even though both can come from ethanol.
The language of naming. To name these compounds we use IUPAC nomenclature, a stem for the number of carbons and a suffix for the functional group, with a locant number to fix where a double bond or group sits, and an alkyl group such as methyl or ethyl naming any branch. Alongside naming sits isomerism, the existence of compounds with the same molecular formula but different structures; butane and 2-methylpropane are the standard structural isomers. A common slip is to treat isomers as members of a homologous series, but isomers share a molecular formula while successive members of a series differ by CH₂.
The named reactions that connect the map. A short set of reactions moves you between the families, and each is a vocabulary item in its own right. Combustion burns a compound in oxygen, cleanly to carbon dioxide and water in plenty of air, or incompletely to carbon monoxide and soot when air is short. Substitution replaces an atom on a saturated alkane, only in ultraviolet light; addition opens the double bond of an alkene and needs no light. That substitution–addition pair is the reaction that most rewards careful wording. Hydrogenation adds hydrogen across a C=C over a nickel catalyst to harden oils into fats. Polymerisation joins many alkene monomers into a polymer. Fermentation makes ethanol from glucose, while oxidation of ethanol with acidified potassium dichromate(VI) gives a carboxylic acid, and dehydration removes water from an alcohol to give back an alkene. Finally esterification joins a carboxylic acid and an alcohol, with concentrated sulfuric acid as catalyst, to form an ester and water, closing the loop between the two oxygen-bearing series.
Ethanol sits at the centre of this map as a hub that connects many reactions: it is made from an alkene by hydration or from glucose by fermentation, it is oxidised to ethanoic acid, dehydrated back to ethene, and reacted with an acid to form an ester. Mastering this one compound therefore explains a large part of the chapter. Keep the physical trend in mind too: within any homologous series the boiling point rises and the volatility falls as the molecules get larger, a pattern often tested alongside the names and formulae.
These terms build directly on bonding and the mole from earlier chapters and underpin the essays and structure questions that Carbon Compounds is known for. Our teachers walk students through this vocabulary in its connected order in online one-to-one lessons, in English, from RM50 an hour, so the wording that SPM Chemistry rewards comes out naturally under exam pressure.
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