They form a homologous series represented by CnH2n+1X They are
further classified as primary, secondary or tertiary according to the
nature of carbon to which halogen is attached If halogen is attached to
a primary carbon atom in an alkyl halide, the alkyl halide is called
primary alkyl halide or 1° alkyl halide Similarly, if halogen is attached
to secondary or tertiary carbon atom, the alkyl halide is called
secondary alkyl halide (2°) and tertiary (3°) alkyl halide, respectively