Question

Nuclear charge increases in a period as well as group. However, periodic properties such as atomic size and IP show a reverse trend. Why?

Answer 1

Nuclear charge increases but in a period, electrons enter into the same shell but in a group, they enter into different shells. When they are in same shells, protons attract easily because of the uniform distance of all electrons. Thus the ionization enthalpy increases.

But in different shells, shielding effect came into existence which increases the atomic size and decreases IP.

So atomic size and IP show reverse trend along a period and group.