What is meant by atomic and ionic radii ? Explain giving reason Why the size of `C1^(-)` ion is bigger than that of `C1` atom whereas size `Na^(+)` ion is smaller than that of Na atom ?

Explanation

### Step-by-Step Solution:

1. **Definition of Atomic and Ionic Radii:**
- **Atomic Radius:** The atomic radius is defined as the distance from the nucleus of an atom to the outermost shell of electrons. It represents the size of a neutral atom.
- **Ionic Radius:** The ionic radius is the distance from the nucleus of an ion to the outermost shell of electrons. It represents the size of an ion, which can be either positively charged (cation) or negatively charged (anion).

2. **Comparison of Cl⁻ Ion and Cl Atom:**
- The chlorine atom (Cl) has 17 protons and 17 electrons, with 7 electrons in its outermost shell (valence shell). When chlorine gains an electron to become Cl⁻, it now has 8 electrons in its valence shell.
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