What is the difference between the first member of a group and the other elements in the $s$- and $p$-block? Why?

(N/A) The first member of each group differs from the other elements in the same group due to their small size,high charge density,and high electronegativity.
$(i)$ Smaller atomic and ionic radii: The first member has a significantly smaller atomic and ionic radius compared to the subsequent members of the same group.
$(ii)$ Absence of $d$-orbitals: The first member of each group has only four valence orbitals $(2s, 2p_x, 2p_y, 2p_z)$ available for bonding,limiting its maximum covalency to $4$ (e.g.,Boron forms $[BF_4]^-$,while Aluminium can form $[AlF_6]^{3-}$).
$(iii)$ Ability to form $p_{\pi}-p_{\pi}$ multiple bonds: The first member of $p$-block elements has a greater ability to form $p_{\pi}-p_{\pi}$ multiple bonds with itself (e.g.,$C=C, C \equiv C, N=N, N \equiv N$) and with other elements of the second period (e.g.,$C=O, C=N, N=O$),whereas heavier elements do not form such bonds effectively.