Explain why are cations smaller and anions larger in radii than their parent atoms?

Question: Explain why are cations smaller and anions larger in radii than their parent atoms?

Cations are smaller and anions are larger in radius than their parent atoms due to the change in the number of electrons in the outermost shell.

When an atom loses one or more electrons to form a cation, the number of electrons in the outermost shell decreases. This causes the remaining electrons to be attracted more strongly to the nucleus, resulting in a decrease in the atomic radius. Additionally, the effective nuclear charge (the net positive charge experienced by an electron in the outermost shell) increases as the number of electrons in the outermost shell decreases, leading to a stronger attraction between the nucleus and the remaining electrons and further decreasing the size of the cation.

On the other hand, when an atom gains one or more electrons to form an anion, the number of electrons in the outermost shell increases. This results in an increase in the repulsion between the electrons, leading to an increase in the atomic radius. Additionally, the effective nuclear charge decreases as the number of electrons in the outermost shell increases, leading to a weaker attraction between the nucleus and the outermost electrons and further increasing the size of the anion.

Overall, the size of an ion is determined by the balance between the attractive force of the nucleus on the electrons and the repulsive force of the electrons on each other. The addition or removal of electrons changes this balance, resulting in the difference in size between cations and anions compared to their parent atoms.