What is electronic concept of valency

Valency of an atom is defined as its combining capacity or combining power.However the valency is also defined on the basis of electronic configuration of elements.This electronic concept of valency is also known as The electronic theory of valency.This theory was originated by Kossel and Lewis independently and applied by Langmuir. According to this theory-- every element has a tendency to acquire inert electronic configuration (ns²np⁶) of the nearest inert gas because it is considered as the most stable configuration (stable octet).Noble gases like neon,argon etc. do not participate in bonding due to the presence of octet of electrons(8 e-s in valence shell).Other elements have less than 8e-s in the valence shell so they participate in chemical combination.This noble gas configuration is attained by either--
(i) transference of electrons which leads to formation of ionic bonding.One of the element called as metal loses its electrons and transfer or donate e-s to another element called as non-metal.Metal loses its e- forms cation and another gains e- and forms anion.
(ii) sharing of electrons leads to formation of covalent bonding.Depending on no. of e-s shared,this may be single,double or triple covalent bonding.