Question

Define valency and valence shell.

Answer 1

1. Valency could be defined as the maximum number of electrons lost or gained by an atom in order to get a complete octet.
2. For example- the valency of chlorine ($\mathrm{Cl}$) is $1$. It gains $1$ electron.
3. Valence shell is the outermost orbit of an atom containing valence electrons.
4. For example Chlorine ($\mathrm{Cl}$) has $7$ electrons in its outermost shell.