The bond angle in `PH _(3)` would be expected to be close to

Options

A. `90^(@)`
B. `105^(@)`
C. `109^(@)`
D. `120^(@)`

Answer

To determine the bond angle in PH₃ (phosphine), we can follow these steps:

### Step 1: Determine the Valence Electrons
Phosphorus (P) is in Group 15 of the periodic table and has 5 valence electrons. Each hydrogen (H) atom has 1 valence electron. Therefore, in PH₃:
- Total valence electrons = 5 (from P) + 3 × 1 (from 3 H) = 8 valence electrons.

### Step 2: Identify Bonding and Lone Pairs
In PH₃, phosphorus forms three single bonds with three hydrogen atoms. This means:
- 3 bond pairs (from the P-H bonds).
- 2 electrons remain as a lone pair on phosphorus.

### Step 3: Analyze the Molecular Geometry
The presence of the lone pair affects the geometry. PH₃ adopts a trigonal pyramidal shape due to the three bond pairs and one lone pair. However, the lone pair does not participate in hybridization because it resides in a pure s orbital.

### Step 4: Consider the Bond Angle
In a perfect tetrahedral arrangement (which would have bond angles of 109.5°), the presence of a lone pair typically reduces the bond angle between the bond pairs. In PH₃, the bond angle is influenced by the lone pair-bond pair repulsion.

### Step 5: Estimate the Bond Angle
Given that the lone pair is non-directional and does not exert significant repulsion on the bond pairs, the bond angle in PH₃ is expected to be less than 109.5°. The bond angle is approximately 93° due to the geometry and the presence of the lone pair.

### Conclusion
The bond angle in PH₃ would be expected to be close to **90 degrees**.

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