The valence of representative elements is either equal to the number of valence electrons or eight minus the number. What is the basis of their rule?
| Group | 1 | 2 | 13 | 14 | 15 | 16 | 17 |
| Compounds | LiH | BeH2 | BH3 | CH4 | NH3 | H2O | HF |
| No. of valence electrons | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| Valency of element | 1 | 2 | 3 | 4 | 8-5 =3 | 8-6 =2 | 8-7 =1 |
From the above table, it is clear that valency of the representative elements of groups 1, 2, 13 and 14 is equal to the number of valence electrons. But the valency of representative elements of group 15, 16 and 17 is equal to eight minus number of valence electrons.
The valency of any element is the number of electrons which it loses, joins or shares with other atoms to attain the nearest inert gas configuration. The elements of groups 1, 2 and 13 lose 1, 2 and 3 electrons respectively to attain the nearest noble gas configuration. Thus, the valency of the elements of groups 1, 2 and 13 is equal to the number of their valence electrons. The elements of group 14 have four electrons in their respective valence shells and thus attain noble gas configuration only by sharing with four more electrons of other atoms. Therefore, the valency of elements of group 14 is also equal to the number of their valence electrons.
The elements of group 15, 16 and 17 have 5, 6 and 7 electrons in their respective valence shells and hence they acquire 3 (8-5), 2 (8-6) and 1 (8-7) electrons either by gaining or sharing electrons from other atoms to attain the nearest inert gas configuration. Thus, the valency of the elements of groups 15, 16 and 17 is equal to eight minus the number of electrons in their respective valence shells.
