Question

With reference to butane, explain the following terms:
(i) Molecular formula
(ii) Structural formula
(iii) Condensed formula

Answer 1

(i) Molecular formula: The formula of an organic compound that represents the kind and the number of each atom present in one molecule is called a molecular formula.

The molecular formula of butane is C₄H₁₀. It shows that butane contains two kinds of atoms; carbon (C) and hydrogen (H). The formula also tells us that one molecule of butane consists of 4 C-atoms and 10 H-atoms

(ii) Structural formula: This formula gives the number of atoms as well as shows how the atoms are connected to one another. The bonds between atoms are represented by lines connecting the element symbols.

The four carbon atoms of a molecule of butane bond together to form a straight chain or a branched chain. Each outer carbon is bonded to three hydrogen atoms, and the inner carbon atom is bonded to one or two hydrogen atoms. This arrangement results in the following structural formulae for butane:




(iii) Condensed formula: The arrangement of atoms in the molecule are shown but the bonds (some or all) between them are omitted and the number of identical groups attached to an atom are indicated by a subscript, i.e., the condensed structural formula basically shows the structural units present. Hence, the condensed structural formulae for butane may be shown as:
CH₃-CH₂-CH₂-CH₃ or CH₃CH₂CH₂CH₃ or C₄H₁₀.