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, we can follow these steps:

### Step 1: Identify the Central Atom and Its Valence Electrons
- The central atom in PH₃ is phosphorus (P).
- Phosphorus has 5 valence electrons.

### Step 2: Count the Number of Attached Atoms
- In PH₃, there are 3 hydrogen (H) atoms attached to the phosphorus atom.

### Step 3: Calculate the Steric Number
- The formula for calculating the steric number (SN) is:
\[ \text{SN} = \frac{1}{2} \left( V + M + C - A \right) \]
where:
- \( V \) = number of valence electrons of the central atom (5 for P)
- \( M \) = number of monovalent atoms attached (3 for H)
- \( C \) = charge of anions (0 for neutral PH₃)
- \( A \) = charge of cations (0 for neutral PH₃)

- Plugging in the values:
\[ \text{SN} = \frac{1}{2} \left( 5 + 3 + 0 - 0 \right) = \frac{8}{2} = 4 \]

### Step 4: Determine the Hybridization
- A steric number of 4 indicates that the hybridization of phosphorus in PH₃ is sp³.

### Step 5: Analyze the Geometry
- The ideal geometry for sp³ hybridization is tetrahedral.
- However, in PH₃, there are 3 bond pairs (P-H bonds) and 1 lone pair.

### Step 6: Adjust for Lone Pair Repulsion
- The presence of a lone pair affects the bond angles. Lone pair-bond pair repulsions are greater than bond pair-bond pair repulsions.
- This causes the bond angles to be smaller than the ideal tetrahedral angle of 109.5°.

### Step 7: Estimate the Bond Angle
- In PH₃, the bond angle is reduced due to the lone pair, resulting in a bond angle close to 93.5°.
- Therefore, the bond angle in PH₃ is expected to be close to 90°.

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

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