Class 11 Chemistry Formula Sheet 2026-27

8.6 FUNCTIONAL GROUPS, RESONANCE AND ESTIMATION OF ELEMENTS

In an organic molecule, the reactions that the compound undergoes are largely decided by a particular atom or small group of atoms present in it, known as the functional group. The hydroxyl group of alcohols, the formyl group of aldehydes and the carboxyl group of acids are familiar examples. Compounds having the same functional group and differing from one another by a –CH₂– unit form a homologous series and show a gradual change in physical properties along the series.

For some molecules a single Lewis structure is unable to explain all the observed properties. In such cases two or more structures, which differ only in the arrangement of electrons, are written. None of these structures exists by itself; the real molecule is a hybrid of them and is more stable than any one of the contributing forms.

To find the percentage of carbon and hydrogen in a compound, a weighed sample is heated strongly with copper(II) oxide so that carbon is converted to carbon dioxide and hydrogen to water. These products are absorbed separately and weighed, and the percentages are calculated from the masses obtained.