Which of the following compounds does not follow the octet rule the electron distribution

Options

A. `PCl_(5)`
B. `PCl_(3)`
C. `H_(2)O`
D. `PH_(3)`

Explanation

To determine which of the following compounds does not follow the octet rule, we will analyze each compound's electron distribution and bonding.

### Step-by-Step Solution:

1. **Understanding the Octet Rule**:
- The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable electronic configuration with eight electrons in their valence shell.

2. **Analyzing PCl5**:
- **Phosphorus (P)** has 5 valence electrons (atomic number 15).
- **Chlorine (Cl)** has 7 valence electrons (atomic number 17).
- In PCl5, phosphorus is the central atom bonded to 5 chlorine atoms.
- Phosphorus shares its 5 valence electrons with 5 chlorine atoms, forming 5 bonds.
- This results in phosphorus having 10 electrons around it (5 bond pairs), which means it has expanded its octet.
- **Conclusion**: PCl5 does not follow the octet rule.

3. **Analyzing PCl3**:
- In PCl3, phosphorus shares its 5 valence electrons with 3 chlorine atoms.
- Each chlorine shares one electron with phosphorus, leading to a total of 8 electrons around phosphorus (3 bond pairs and 1 lone pair).
- **Conclusion**: PCl3 follows the octet rule.

4. **Analyzing H2O**:
- Oxygen has 6 valence electrons and needs 2 more to complete its octet.
- Each hydrogen shares one electron with oxygen, resulting in 8 electrons around oxygen.
- **Conclusion**: H2O follows the octet rule.

5. **Analyzing PH3**:
- Phosphorus shares its electrons with 3 hydrogen atoms.
- Each hydrogen atom contributes one electron, leading to a total of 8 electrons around phosphorus (3 bond pairs and 1 lone pair).
- **Conclusion**: PH3 follows the octet rule.

### Final Conclusion:
The compound that does not follow the octet rule is **PCl5**.