Answer
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When an element forms an anion, the radius increases. This is because an anion gains electrons, leading to increased electron-electron repulsion and a larger electron cloud, resulting in a larger atomic radius.
When an element forms a cation, the radius decreases. This is because a cation loses electrons, leading to a reduced electron-electron repulsion and a smaller electron cloud, resulting in a smaller atomic radius.
Isoelectronic refers to atoms or ions that have the same number of electrons. When comparing sizes of ions in an isoelectronic series, the ion with the largest positive charge (fewest electrons) will have the smallest radius, and the ion with the largest negative charge (most electrons) will have the largest radius. This is because as the number of protons increases, the attractive force on the electrons increases, leading to a smaller radius, while as the number of electrons increases, the repulsive force between electrons increases, leading to a larger radius.
