Ionic Size

Cations  

- Definition: Cations are formed when an atom loses electrons.  

- Effect on Size:  

  - Loss of electrons often leads to loss of an entire shell.  

  - The effective nuclear charge on the remaining valence electrons becomes greater.  

  - As a result, cations have smaller ionic radii compared to their corresponding atomic radii.  

Anions  

- Definition: Anions are formed when an atom gains electrons.  

- Effect on Size:  

  - Addition of electrons increases electron‑electron repulsion.  

  - This can expand the electron cloud and sometimes add to the number of shells.  

  - Consequently, anions have larger ionic radii compared to their corresponding atomic radii.  

Key Insight  

- Cations → Smaller than atoms (due to electron loss and stronger nuclear pull).  

- Anions → Larger than atoms (due to electron gain and increased repulsion).