Why carbon forms many compounds

Carbon has four outer-shell electrons and normally forms four covalent bonds. Carbon atoms bond strongly to one another, allowing straight chains, branched chains and molecules containing functional groups. Organic chemistry studies carbon compounds, especially hydrocarbons and their derivatives. Carbon oxides, carbonates and a few other simple carbon compounds are usually treated separately.

Carbon skeletons

The carbon skeleton is the connected arrangement of carbon atoms. A skeleton may be one carbon atom, a straight chain or a branched chain. Hydrogen atoms complete carbon valencies unless other atoms or groups are attached. The same carbon skeleton can carry different functional groups and therefore show very different chemical behaviour.

Functional groups

A functional group is an atom or group of atoms that determines characteristic chemical properties. The C=C group makes alkenes undergo addition, -OH identifies alcohols, -COOH identifies carboxylic acids, and -COO- occurs in esters. Recognising the group is often faster than interpreting an entire formula.

Structure controls reaction

Organic reactions usually involve a functional group or a particular bond rather than every bond in the molecule. For example, alkane substitution involves C-H bonds, while alkene addition involves the C=C bond. Careful formula interpretation therefore predicts both naming and reaction products.

High-value recall and connections

Essential recall: How many covalent bonds does carbon usually form? Four. What is a functional group? An atom or group of atoms that determines characteristic chemical properties. Why are there many carbon compounds? Carbon forms strong bonds to itself and other atoms, producing chains, branches and functional groups. Practical connection: Use molecular model kits to make methane, ethane, ethene and ethanol. Check that every carbon has four bonds and identify the functional group where present. Examination connection: Count the bonds around each carbon. A double bond counts as two covalent bonds.

Review questions and suggested answers