Atomic Structure and Chemical Bonding — CHEMISTRY STD 9 — Question

Elements tend to combine with one another to attain the stable electronic configuration of the nearest inert gas.
Sodium chloride
The sodium atom has 1 electron in the valence shell which it donates to the chlorine atom with 7 electrons in the valence shell to attain the stable electronic configuration of the nearest inert gas, i.e. 8 electrons in the valence shell. This is known as the octet rule. These elements combine to form sodium chloride.