Give reasons for:

(i) alkanes are said to be saturated organic compounds

(ii) alkenes are known as olefins

(iii) alkenes are more reactive than alkanes

(iv) ethanoic acid is known as an aliphatic monocarboxylic acid.

(i) In alkanes, all the four valencies of each carbon atom are satisfied by the hydrogen atoms, forming single covalent bond. The non-availability of electrons in the single covalent bond makes them less reactive and therefore they undergo substitution reaction only. Hence, they are called saturated hydrocarbon.

(ii) Alkenes are known as olefins [Oleum = oil; ficare = to make] because they form oily products on treatment with halogens (like chlorine or bromine).

(iii) Alkenes are unsaturated hydrocarbons having carbon atoms forming a double covalent bond as their valencies are not fully satisfied by hydrogen atoms whereas alkanes are saturated hydrocarbons as all the four valencies of its carbon atoms are satisfied by the hydrogen atoms. The availability of electrons in the double bond in case of alkenes makes them more reactive than alkanes which has do not have electrons available in the single covalent bond.

(iv) Ethanoic acid (CH₃ – COOH) contains only one – COOH group (carboxylic acid group) that is why it is called a monocarboxylic acid. As ethanoic acid does not contain a benzene ring, so it is an aliphatic monocarboxylic acid.