Describe the theory associated with the radius of an atom as it
a. gains an electron
b. loses an electron

Explanation

(a) Gain of electron . When a neutral atom gains one electron to form an anion its radius increaeses. The reason being that the number of electrons in the anion increases while its nuclear charge remains the same as the parent atom. Since the same nuclear charge now attracts greater number of electrons therefore force of attraction of the nucleus on the electrons of the shells decreases (i.e., effective nuclear charge decreases ) and hence the electron cloud expands. In other words the distance between the centre of the nucleus and the last shell that contains electrons increases thereby increasing the ionic radius . Thus

( b) Loss of electrons. When a neutral atom loses one electron to form a cation its atomic radius decreases. The reason being that the number of electrons in the cation decreases while its nuclear charge remains the same as the parent atom. Since the same nuclear charge now attracts lesser number of electrons therefore the force of attraction of the nucleus of electrons of all the shells- increases (i.e., effective nuclear charges increases ) and hence the size of cation decreases. Thus