Organic and inorganic
Compounds containing carbon are mostly called organic compounds. A few carbon-containing substances such as carbon dioxide (CO2), carbonates and metal carbides are counted as inorganic. Organic chemistry is dominated by carbon because a carbon atom forms four covalent bonds and can link to other carbon atoms in chains and rings — a property called catenation.
Hydrocarbons and derivatives
Hydrocarbons contain only carbon and hydrogen. They are divided into saturated hydrocarbons (only single C–C bonds, such as the alkanes) and unsaturated hydrocarbons (with double or triple bonds, such as the alkenes). Other organic families contain extra elements: alcohols (–OH), carboxylic acids (–COOH) and esters (–COO–).
| Family | Example |
|---|---|
| Alkane | CH4 |
| Alkene | C2H4 |
| Alcohol | C2H5OH |
| Carboxylic acid | CH3COOH |
Worked example
Classify ethanol, C2H5OH. It contains carbon, so it is organic. It contains the –OH group, so it belongs to the alcohol family, not the hydrocarbons — even though it also has C and H, the oxygen-containing group defines its class.
Beyond these families, organic chemistry also includes esters (sweet-smelling compounds made from an alcohol and an acid) and, at higher levels, halogenoalkanes, aldehydes, ketones and amines. Carbon compounds form the basis of fuels, plastics, medicines and all living tissue. A molecular formula shows the actual number of atoms present, while a structural formula shows how those atoms are joined; both are useful when deciding which family a compound belongs to.
Remember
- Most carbon compounds are organic; CO2 and carbonates are inorganic.
- Hydrocarbons contain only C and H.
- Saturated = single bonds only; unsaturated = has C=C or C≡C.
- Functional groups define the chemical family.