Question

The size of a cation is smaller than the parent atom while the size of the anion is larger than its parent atom . explain

Answer 1

Answer:

(1) An anion is formed by the acceptance of an electron by a parent atom.

A + e^- → A^-

(2) The nuclear charge in a parent atom and its anion is same.

(3) The additional electron in an anion, results in the repulsion among the electrons and results in the decrease in effective nuclear charge, as compared to the parent atom. Therefore, the radius of an anion is larger than its parent atom. For example, F atom has atomic radius 64 pm while anion F has ionic radius 136 pm

Answer 2

The size of a cation is smaller than its parent atom because-

• We already know that cations are formed due to the loss of one or more electrons from the parent gaseous atom.
• But, even after the loss of electrons, the nuclear charge of the parent gaseous atom remains the same.
• Due to this the effective nuclear charge on the remaining electrons increases and so the remaining electrons are held closer to the nucleus.
• This results in a decrease in the size of the charged atom.

The size of an anion is larger than its parent atom because-

• We know that anions are formed due to the gain of one or more electrons in the parent atom.
• Nuclear charge remains the same in this case too.
• Due to this the effective nuclear charge per electron decreases and the electrons go further away from the nucleus.
• This results in anions being greater in size than their parent atoms.