The correct sequence regarding bond angle

Options

A. Option 1. `NH_(3) gt PH_(3) gt AsH_(3)`
B. Option 2. `NH_(3) = PH_(3) = AsH_(3)`
C. Option 3. `AsH_(3) gt PH_(3) gt NH_(3)`
D. Option 4. `PH_(3) gt NH_(3) gt AsH_(3)`

Answer

To determine the correct sequence regarding bond angles for NH3 (ammonia), PH3 (phosphine), and AsH3 (arsine), we can analyze the molecular structures and the factors affecting bond angles. Here’s a step-by-step solution:

### Step-by-Step Solution:

1. **Identify the Molecular Structures**:
- NH3 has a trigonal pyramidal shape due to one lone pair on nitrogen.
- PH3 has a similar structure but with phosphorus as the central atom.
- AsH3 also has a trigonal pyramidal shape with arsenic as the central atom.

2. **Determine Hybridization**:
- All three molecules (NH3, PH3, AsH3) exhibit sp³ hybridization because they each have four regions of electron density (three bond pairs and one lone pair).

3. **Consider Electronegativity**:
- Electronegativity decreases as we move down the group in the periodic table. Thus, nitrogen (N) is more electronegative than phosphorus (P), which is more electronegative than arsenic (As).
- This affects the bond angles due to the repulsion between the bond pairs and the lone pair.

4. **Analyze Bond Pair Repulsion**:
- In NH3, the bond pairs are closer to the nitrogen nucleus, leading to greater repulsion and a larger bond angle.
- In PH3, the bond pairs are further from the phosphorus nucleus, resulting in less repulsion and a smaller bond angle than NH3.
- In AsH3, the bond pairs are even further from the arsenic nucleus, leading to the least repulsion and the smallest bond angle.

5. **Establish the Bond Angle Trend**:
- The bond angles can be summarized as follows:
- NH3 > PH3 > AsH3
- This indicates that as we move down the group from nitrogen to arsenic, the bond angle decreases.

6. **Conclusion**:
- Therefore, the correct sequence regarding bond angles is:
- NH3 > PH3 > AsH3