Question

Why is atomic density of K less than Na

Answer 1

Potassium (K) is lighter than Sodium (Na) because of abnormal increase in the size of potassium. In the group, not only the atomic size but also the mass increases, but the increase in atomic mass more compansates the bigger atomic size and so the density naturally increases. But, in potassium the atomic radius increases highly whereas the mass is smaller in comparison to size and so the density of K decreases and it becomes lighter than Sodium Na.