Fluorine has the highest electronegativity among the group on the Pauling scale, but the electron affinity of fluorine is less than that of chlorine because

Options

A. The atomic number of fluorine is less than that of chlorine
B. Fluorine being the first member of the family behaves in an unuseual manner
C. Chlorine can accommodate an electron better than fluorine by untilising its vacant `3d` orbital
D. Small size, high electron density and an increases electron repulsion make addition of an electron to fluorine less favourable than that in the case of chlorine

Answer

To understand why fluorine has a lower electron affinity than chlorine despite having the highest electronegativity, we can break down the reasoning into several steps:

### Step-by-Step Solution

1. **Understanding Electronegativity and Electron Affinity**:
- Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.
- Electron affinity refers to the amount of energy released when an electron is added to a neutral atom to form a negative ion.

2. **Comparing Sizes of Fluorine and Chlorine**:
- Fluorine (F) is smaller in size compared to chlorine (Cl). The atomic radius of fluorine is less than that of chlorine due to its position in the periodic table.

3. **Shielding Effect**:
- In multi-electron atoms, electrons in inner shells repel the valence electrons. This phenomenon is known as the shielding effect.
- In fluorine, the shielding effect is more pronounced due to its small size and high electron density, which leads to greater electron-electron repulsion.

4. **Electron Affinity of Fluorine**:
- When an electron is added to fluorine, the increased electron-electron repulsion due to its small size makes the addition of an electron less favorable.
- Therefore, even though fluorine is highly electronegative, the energy released when it gains an electron (its electron affinity) is less than that of chlorine.

5. **Chlorine's Ability to Accommodate Electrons**:
- Chlorine has empty d-orbitals that can accommodate additional electrons. This allows chlorine to stabilize the added electron better than fluorine can.
- The presence of these empty orbitals in chlorine reduces the repulsive forces experienced when an electron is added, thus increasing its electron affinity.

6. **Conclusion**:
- The combination of fluorine's small size, high electron density, and the resultant electron-electron repulsion makes the addition of an electron less favorable compared to chlorine, which can better accommodate the added electron due to its larger size and available d-orbitals.

### Final Answer:
Fluorine has the highest electronegativity but a lower electron affinity than chlorine because its small size and high electron density lead to increased electron-electron repulsion, making the addition of an electron less favorable compared to chlorine, which can accommodate an electron better due to its larger size and empty d-orbitals.