The statement that the size of an ion is greater than its parent atom is not always true. It depends on whether the ion is a cation (positively charged) or an anion (negatively charged). Here's why:

1. Cations:

* Smaller than the parent atom: When an atom loses electrons to become a cation, it loses an electron shell or reduces the size of its outermost shell. This is because the number of protons in the nucleus remains the same, while the number of electrons decreases. The stronger attraction between the protons and the remaining electrons pulls them closer to the nucleus, resulting in a smaller ionic radius.

2. Anions:

* Larger than the parent atom: When an atom gains electrons to become an anion, it adds electrons to its outermost shell. This increases the electron-electron repulsion within the shell, causing the shell to expand. The increased repulsion outweighs the increased attraction between the nucleus and the additional electrons, resulting in a larger ionic radius.

In summary:

* Cations are smaller than their parent atoms.

* Anions are larger than their parent atoms.

Example:

* Sodium (Na) atom has a radius of 186 pm.

* Sodium ion (Na+) has a radius of 102 pm, smaller than the atom.

* Chlorine (Cl) atom has a radius of 99 pm.

* Chloride ion (Cl-) has a radius of 181 pm, larger than the atom.