Which type of periodicity is exhibited by periodic table following properties of element:

(i) Atomic radii

(ii) Ionisation enthalpy

(iii) Electronegativity

(i) As we go down a group, the number of shells increases and hence the atomic radii increases. Along a period, the number of shells remain the same, but the effective nuclear charge increases from left to right. This means that there is an increased force of attraction between nucleus and the electrons causing the atomic radii to decrease along a period.

(ii) Ionisation enthalpy is the energy required to remove an electron from an isolated gaseous atom. Ionisation enthalpy decreases down the group because the increased atomic radii down the group cause a decrease in the effective nuclear charge. There will be less force of attraction between nucleus and outermost electron, from which electron can be removed by supplying a small amount of energy.

When going from left to right, the atomic radii decreases and the effective nuclear charge increases. The electron removal process would be more difficult, and it requires more amount of energy. Hence ionization enthalpy increases from left to right in a period.

(iii) Electronegativity is the relative tendency of an element to attract the bonded shared electrons towards it.

Going from top to bottom in a group, the atomic radii increases and the effective nuclear charge decreases. Due to this reason, the elements would give up the electrons more easily. Thus electronegativity decreases down the group.

Going from left to right, there is an increase in effective nuclear charge and decrease in atomic radii. The increased force of attraction of nucleus would attract the shared electrons to itself. Thus electronegativity increases from left to right in a period.