- A cation is formed by the loss of one or more electrons, therefore, it contains fewer electrons that the parent atom but has the same nuclear charge.
- As a result, the shielding effect is less and effective nuclear charge is larger within a cation. Thus, radius of a cation is smaller than the parent atom.
- However, an anion is formed by the gain of one or more electrons and therefore, it contains a greater number of electrons than the parent atom.
- Due to these additional electrons, anion experiences increased electronic repulsion and decreased effective nuclear charge. As a result, an anion has larger radius than its parent atom.
Hence, radius of a cation is smaller and that of an anion are larger as compared to that of their parent atoms.