Question

Why alkane series is formed by replacing one H atom of an alkane by CH3 group?

Answer 1

Alkanes have only carbon and hydrogen. Each carbon has a valency=4. So we have to add something after removing hydrogen. To go to the next higher alkane, it should have one extra carbon. But we cannot simply add a carbon alone because carbon is tetravalent. Since on addition of this extra carbon, it forms a bond with the carbon which has initially lost H, 3 more bonds are left for the extra added carbon. Since alaknes can have only C and H, we add 3 H to the added carbon which forms a CH3 group. So the higher memeber is obtained by adding CH3 groups.