Discuss variations in atomic radii and ionization enthalpies in halogens.

(N/A) $(i)$ 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 the second period,is extremely small. Atomic radii and ionic radii increase from fluorine to iodine due to the increasing number of quantum shells.
$(ii)$ Ionization enthalpies: Halogens have very high ionization enthalpy,which indicates that they have very little tendency to lose an electron. The ionization enthalpy decreases down the group from fluorine to iodine due to the increase in atomic size. Iodine has the maximum tendency to lose an electron $(I^+)$ because of its large size and low ionization enthalpy.