as diagonal relationship in the periodic properties. What are the reasons for the different chemical behaviour of the first member of a group of elements in the s- and p- blocks compared to that of the subsequent members in the same group? The anomalous behaviour is attributed to their small size, large charge/ radius ratio and high electronegativity of the elements. In addition, the first member of group has only four valence orbitals ( s and p ) available for bonding, whereas the second member of the groups have nine valence orbitals ( s , p , d ).
As a consequence of this, the maximum covalency of the first member of each group is (e.g., boron can only form BF