Consequently there are six groups of $p$-block elements in the periodic table numbering from $13$ to $18$ . Boron, carbon, nitrogen, oxygen, fluorine and helium head the groups. Their valence shell electronic configuration is $n s^{2} n p^{1-6}$ (except for $He$).

The inner core of the electronic configuration may, however, differ. The difference in inner core of elements greatly influences their physical properties (such as atomic and ionic radii, ionisation enthalpy, etc.) as well as chemical properties.

Consequently, a lot of variation in properties of elements in a group of $p$-block is observed. The maximum oxidation state shown by a $p$-block element is equal to the total number of valence electrons (i.e., the sum of the $s$ and $p$-electrons).

The important oxidation states exhibited by $p$-block elements are shown in table. In boron, carbon and nitrogen families the group oxidation state is the most stable state for the lighter elements in the group.

However, the oxidation state two unit less than the group oxidation state becomes progressively more stable for the heavier elements in each group.

The occurrence of oxidation states two unit less than the group oxidation states are sometime attributed to the 'inert pair effect'.