CBSE Class 10 Science 2019 · Paper 31/3/2 · Question 20

Structural isomers: compounds that have the same molecular formula but different structures are called structural isomers. Characteristics of isomers: 1. They have the same molecular formula. 2. They have the same molecular mass and the same number of each kind of atom. 3. They have different structures. 4. They have different physical and chemical properties (for example, butane boils at about $-0.5{}^{\circ }\text{C}$ and isobutane at about $-11.7{}^{\circ }\text{C}$). Possible structures of butane, ${\text{C}}_4{\text{H}}_{10}$: (i) butane (n-butane), a straight chain of four carbon atoms, ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_3$; (ii) isobutane (2-methylpropane), a chain of three carbon atoms with the fourth attached to the middle carbon, ${\text{CH}}_3-\text{CH}({\text{CH}}_3)-{\text{CH}}_3$.