Describe the theory associated with the radius of an atom as it:
$(a)$ gains an electron
$(b)$ loses an electron

(N/A) When an atom gains an electron,it forms an anion. The addition of an electron increases the interelectronic repulsion,while the nuclear charge remains constant. This causes the electron cloud to expand,leading to an increase in the ionic radius compared to the atomic radius.
$(b)$ When an atom loses an electron,it forms a cation. The removal of an electron decreases the interelectronic repulsion,while the nuclear charge remains constant. This results in a stronger pull by the nucleus on the remaining electrons,leading to a decrease in the ionic radius compared to the atomic radius.