(i) The number of electrons gained, lost or shared to make the octet of electrons (in the outermost shell), gives us directly the combining capacity of the element, that is, the valency.
(ii)
Elements | Atomic No. | Electronic configuration | Valency |
Chlorine | 17 | 2, 8, 7 | -1 |
Sulphur | 16 | 2, 8, 6 | -2 |
Aluminium | 13 | 2, 8, 3 | +3 |