The `H-O-H` angle in water molecule is about

Options

A. `90^(@)`
B. `180^(@)`
C. `109^(@)28`
D. `104.5^(2)`

Answer

To determine the H-O-H angle in a water molecule (H₂O), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Central Atom**:
In the water molecule, oxygen (O) is the central atom, with two hydrogen (H) atoms bonded to it.

2. **Count Lone Pairs and Bond Pairs**:
Oxygen has two lone pairs of electrons and forms two covalent bonds with hydrogen. Therefore, we have:
- Number of bond pairs = 2 (from the two H-O bonds)
- Number of lone pairs = 2 (on the oxygen atom)

3. **Determine the Steric Number**:
The steric number is calculated as the sum of bond pairs and lone pairs:
\[ \text{Steric Number} = \text{Number of Bond Pairs} + \text{Number of Lone Pairs} = 2 + 2 = 4 \]

4. **Identify the Hybridization**:
A steric number of 4 corresponds to sp³ hybridization.

5. **Determine the Geometry**:
The geometry of a molecule with sp³ hybridization and a steric number of 4 is tetrahedral.

6. **Consider the Shape**:
However, since there are two lone pairs, the shape of the water molecule is bent (or V-shaped), not tetrahedral.

7. **Determine the Ideal Bond Angle**:
In a perfect tetrahedral arrangement, the ideal bond angle is 109 degrees and 28 minutes.

8. **Adjust for Lone Pair Repulsion**:
Lone pairs exert greater repulsive forces than bond pairs. This causes the bond angle to decrease. The bond angle in water is reduced from the ideal tetrahedral angle to approximately 104.5 degrees due to the presence of the two lone pairs.

9. **Select the Correct Answer**:
Among the options given:
- 90 degrees (incorrect)
- 180 degrees (incorrect)
- 109 degrees 28 minutes (incorrect)
- 104.5 degrees (correct)

Thus, the H-O-H angle in a water molecule is approximately **104.5 degrees**.