Define valency by taking examples of silicon and oxygen.
The valency of electrons is determined by electrons present in the outermost shell of an atom. Electrons present in the outermost shell of an atom are known as the valence elctrons. Electrons gain or lose electrons to complete its octet. The valency of silicon is 14 and electronic configuration is 2,8,4. So silicon can gain or lose 4 electrons. So the valency of silicon is +4 or -4. Atomic number of oxygen is 8 and electronic configuration is 2,6. To complete its octet oxygen gain 2 electrons hence the valency of oxygen is 2.
