JEE Advanced2017ChemistryClassification of Elements and Periodicity in PropertiesActual
The colour of the X 2 molecules of group 17 elements changes gradually from yellow to violet down the group. This is due to -
Options
- ADecrease i n H O M O - L U M O gap down the group
- BDecrease in π * - σ * down the group
- CThe physical state of X 2 at room temperature changes from gas to solid down the group
- DDecrease in ionization energy down the group
Correct answer
A. Decrease i n H O M O - L U M O gap down the group
Step-by-step solution
Halogens are coloured due to HOMO-LUMO transition of electrons. On moving down the group HOMO-LUMO energy gap decreases so transition of electrons become easier from Π * 2 p x to σ * 2 p z therefore colour intensify.