Discuss variations in atomic radii and ionization enthalpies in Halogens.

Explanation

(i) Atomic radii : The halogens have the smallest atomic radii in their respective periods due to maximum effective nuclear charge. The atomic radius of fluorine like the other elements of second period is extremely small. Atomic radii and ionic radii increase from fluorine to iodine due to increasing number of quantum shells.
(ii) Ionisation enthalpies : Halogens have very high ionisation enthalpy which indicates that they have very less tendency to lose electron. The ionisation enthalpy decreases down the group from fluorine to iodine due to increase in atomic size. Iodine has maximum tendency to lose electron (I+) because of its large size and low ionisation enthalpy.