Sodium and aluminium have atomic numbers 11 and 13, respectively. They are separated by one element in the periodic table, and have valencies 1 and 3 respectively. Chlorine and potassium are also separated by one element in the periodic table (their atomic numbers being 17 and 19, respectively) and yet both have valency 1. Explain.

Explanation

Na and Al have 1 and 3 valence electrons respectively. They easily lose electron (donate electrons) to form cations for attaining stability. 1 But in the case of Cl and K, they have 7 and 1 valence electrons respectively. Thus, chlorine nearer to octer configuration gain an electron forming anion and attains stability, while potassium having 1 valence electron, lose electron (donate electrons) to form cation and attains stability. Thus, the difference.