Periodicity in valence - among representative elements, the valence is either equal to the number of electrons in the outermost orbitals or 8 - minus this number

What is 8 ? There can be a max of 6 electroins untill p shell and 3 in s shell

Edited August 22Aug 22 by HbWhi5F

Valence refers to the number of electrons in the valence band, OR, the available positions that can be filled in the valence band.
There are, except for certain special orbital states, 8 electrons and available positions in the valence band where bonds to other atoms are made by 'sharing' electrons.
Groups 15 through 18 can either accept 3, 2, or 1 electrons, or give up 5, 6, or 7 electrons to form a bond.

Edited August 22Aug 22 by MigL