Which combination of atoms can form a polar covalent bond?

Options

A. H and H
B. H and F
C. N and N
D. Na and F

Explanation

To determine which combination of atoms can form a polar covalent bond, we need to analyze the electronegativity (E-N) differences between the atoms involved in the bond. Here’s a step-by-step solution:

### Step 1: Understand Polar Covalent Bonds
A polar covalent bond occurs when two atoms share electrons unequally due to a difference in their electronegativities. The greater the difference in electronegativity, the more polar the bond.

### Step 2: Evaluate the Given Combinations
1. **H and H**:
- When two hydrogen atoms bond (H2), they share electrons equally.
- Electronegativity difference = 0 (both are the same atom).
- **Conclusion**: Non-polar covalent bond.

2. **N and N**:
- When two nitrogen atoms bond (N2), they also share electrons equally.
- Electronegativity difference = 0 (both are the same atom).
- **Conclusion**: Non-polar covalent bond.

3. **Na and F**:
- Sodium (Na) has a low electronegativity, while fluorine (F) has a very high electronegativity.
- The bond formed here is ionic (Na donates an electron to F).
- **Conclusion**: Not a covalent bond, hence not polar covalent.

4. **H and F**:
- Hydrogen (H) has a lower electronegativity compared to fluorine (F).
- When they bond, the shared electrons are pulled closer to F due to its higher electronegativity.
- Electronegativity difference is significant.
- **Conclusion**: This forms a polar covalent bond (HF).

### Step 3: Final Conclusion
Among the combinations evaluated, the combination of **H and F** can form a polar covalent bond.

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