Nature of organic compounds

Why carbon makes so many compounds

Organic compounds are based on carbon. Some occur naturally, while others are made synthetically. Carbon can form four covalent bonds, and a carbon atom can bond to another carbon atom. Repeating those carbon–carbon bonds builds a carbon skeleton that can be short or long, straight or branched. A chain can also join back on itself to form a ring. Hydrogen and other atoms can attach to the skeleton, creating still more possibilities.

Compare a straight chain of four carbon atoms with a branched arrangement of four carbon atoms. Both use the same number of carbon atoms, but the atoms are connected differently. Rings add another kind of arrangement. These different structures help explain why carbon gives rise to such a vast array of compounds rather than just a few.

Families within the variety

The many compounds are not all unrelated. Chemists group compounds with similar structures and chemical properties into families, called homologous series. For example, methane ($\mathrm{CH_4}$), ethane ($\mathrm{C_2H_6}$) and propane ($\mathrm{C_3H_8}$) are members of the alkane family. Moving from one to the next adds one carbon atom and two hydrogen atoms—a $\mathrm{CH_2}$ unit—while keeping the same general bonding pattern. Members therefore have similar chemical behaviour, although properties such as boiling point change as the molecules get larger.

Carbon's ability to build varied chains and rings creates many possible structures; grouping related structures into families makes that variety easier to understand. The same bonding possibilities underpin carbon compounds found in living things and those made in laboratories.

Carbon structures

Carbon forms four covalent bonds and bonds to itself. Its atoms can form chains, branched chains and rings, allowing a vast range of natural and synthetic organic compounds.

Families

Related organic compounds form homologous series. The alkanes are one example: successive members differ by $\mathrm{CH_2}$ and have similar chemical properties.