Why are halogens coloured?

Answer

All the halogens are coloured. The colour is due to the reason that their molecules absorb light in the visible is transmitted. The colour of the halogens is actually the colour of this transmitted light.The amount of energy for excitation decreases progressively from `F` to `I` as the size of the atom increases. Consequently, the energy of the transmitted light does on increasing from `F` to `I`.In other words, the colour of the halogens different from `F_(2)` to `I_(2)`.For example `F_(2)` absorbs violet light (higher excitation energy) and hence appears pale yellow while iodine absorbs yellow and green light (lower excitation energy ) and hence appears deep violet. Similarly, we can account for greenish yellow colour of `Cl_(2)` and orange red colour of bromine.