(a) What is a homologous series ? Explain with an example.
(b) State two characteristics of a homologous series.
(c) The molecular formula of an organic compound is C18H36. Name its homologous series.
(d) Select the hydrocarbons which belong to the same homologous series. Give the name of each series.
CH4, C2H2, C2H4, C2H6, C4H10, C3H4, C3H6
(e) What is meant by 'heteroatom'? Give examples. Write the names and formulae of two organic compounds containing different heteroatoms.
(a) Homologous series: A homologous series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group. A homologue of CH3OH will differ by the −CH2 group; therefore, methanol's successive homologue will be ethanol (C2H5OH).
(b) Charecterstics include a general formula and neighbouring members differing by CH2, with similar chemical properties and with a gradation in physical properties. Homologous series are 'families' of organic compounds. They share common characteristics: They all contain the same functional group.
(c) The general formula of the compound is CnH2n. Thus it's an alkene.
(d) Alkane - CH4, C2H6, C4H10
Alkene - C2H4, C3H6
Alkyne - C2H2, C3H4
(e) A heteroatom is any atom that is not carbon or hydrogen. Usually, the term is used to indicate that non-carbon atoms have replaced carbon in the backbone of the molecular structure. Typical heteroatoms are nitrogen (N), oxygen (O), sulfur(S), phosphorus (P), chlorine (Cl)etc.