Why are halogens coloured?

Explanation

Halogens are coloured because their molecules absorb light in the visible region, due to which they get excited to higher energy levels, while the remaining light is transmitted. The colour of the halogens is in fact, the colour of the transmitted light. With increase in atomic size (from F to I), the amount of energy required for excitation decreases. Consequently, the energy of transmitted light increases, which deepens the colour from F to I. For example, `F_(2)` absorbs violet light (higher excitation energy) and appears pale yellow, while iodine absorbs yellow and green light (lower excitation energy) and appears deep violet. Similarly, greenish-yellow colour of Cl and orange-red colour of bromine can be explained.