How will you accout for `104.5^(@)` bond angle in water ?

Explanation

To account for the 104.5° bond angle in water (H₂O), we can follow these steps:

### Step 1: Determine the Central Atom and Its Valence Electrons
- The central atom in water is oxygen (O), which has an atomic number of 8.
- Oxygen has 6 valence electrons.

**Hint:** Remember that the number of valence electrons for an element can be found from its group number in the periodic table.

### Step 2: Count the Bonding and Lone Pairs
- Water forms two single bonds with hydrogen (H), which are monovalent (each H contributes 1 electron).
- Therefore, the total number of electrons involved in bonding is 2 (from the two H atoms).
- The total number of electrons around the oxygen atom is 6 (from O) + 2 (from H) = 8 electrons.

**Hint:** Each bond formed contributes to the total electron count around the central atom.

### Step 3: Calculate the Steric Number
- The steric number can be calculated using the formula:
\[ \text{Steric Number} = \frac{(V + M + C - A)}{2} \]
where:
- \( V \) = number of valence electrons of the central atom (6 for O)
- \( M \) = number of monovalent atoms bonded (2 for H)
- \( C \) = charge of cations (0 for neutral water)
- \( A \) = charge of anions (0 for neutral water)

- Plugging in the values:
\[ \text{Steric Number} = \frac{(6 + 2 + 0 - 0)}{2} = \frac{8}{2} = 4 \]

**Hint:** The steric number helps determine the hybridization and geometry of the molecule.

### Step 4: Determine Hybridization
- A steric number of 4 indicates that the hybridization of the oxygen atom is \( sp^3 \).

**Hint:** Hybridization can be inferred from the steric number: 4 corresponds to \( sp^3 \).

### Step 5: Analyze the Molecular Geometry
- The geometry of \( sp^3 \) hybridized molecules is tetrahedral, which has bond angles of approximately 109.5°.

**Hint:** Tetrahedral geometry is the ideal arrangement for minimizing electron pair repulsion.

### Step 6: Consider the Effect of Lone Pairs
- In the case of water, there are 2 lone pairs of electrons on the oxygen atom.
- According to VSEPR (Valence Shell Electron Pair Repulsion) theory, lone pairs repel more strongly than bonding pairs.

**Hint:** Lone pairs occupy more space and exert greater repulsive forces than bonding pairs.

### Step 7: Adjust the Bond Angle
- The presence of the 2 lone pairs compresses the bond angle between the hydrogen atoms from the ideal tetrahedral angle (109.5°) to approximately 104.5°.

**Hint:** The actual bond angle is less than the ideal angle due to the repulsion caused by the lone pairs.

### Conclusion
Thus, the bond angle in water is 104.5° due to the repulsion between the two lone pairs of electrons on the oxygen atom, which reduces the angle from the ideal tetrahedral angle of 109.5°.

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