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)`

Answer

To determine which compound does not follow the octet rule in its electron distribution, we will analyze each of the given compounds: PCl5, PCl3, water (H2O), and PH3.

### Step-by-Step Solution:

1. **Understanding the Octet Rule**:
- The octet rule states that main group elements tend to bond in such a way that each atom has eight electrons in its valence shell.

2. **Analyzing PCl5**:
- Phosphorus (P) has 5 valence electrons.
- In PCl5, phosphorus forms 5 bonds with 5 chlorine (Cl) atoms.
- Each bond consists of 2 electrons, so:
\[ \text{Total electrons around P} = 5 \text{ bonds} \times 2 \text{ electrons/bond} = 10 \text{ electrons} \]
- Since phosphorus has 10 electrons around it, it does not follow the octet rule.

3. **Analyzing PCl3**:
- Phosphorus has 5 valence electrons.
- In PCl3, phosphorus forms 3 bonds with 3 chlorine atoms and has 1 lone pair.
- The total electron count is:
\[ \text{Total electrons around P} = 3 \text{ bonds} \times 2 \text{ electrons/bond} + 2 \text{ electrons (lone pair)} = 8 \text{ electrons} \]
- Thus, PCl3 follows the octet rule.

4. **Analyzing Water (H2O)**:
- Oxygen (O) has 6 valence electrons.
- In water, oxygen forms 2 bonds with 2 hydrogen (H) atoms and has 2 lone pairs.
- The total electron count is:
\[ \text{Total electrons around O} = 2 \text{ bonds} \times 2 \text{ electrons/bond} + 4 \text{ electrons (lone pairs)} = 8 \text{ electrons} \]
- Therefore, water follows the octet rule.

5. **Analyzing PH3**:
- Phosphorus has 5 valence electrons.
- In PH3, phosphorus forms 3 bonds with 3 hydrogen atoms and has 1 lone pair.
- The total electron count is:
\[ \text{Total electrons around P} = 3 \text{ bonds} \times 2 \text{ electrons/bond} + 2 \text{ electrons (lone pair)} = 8 \text{ electrons} \]
- Hence, PH3 also follows the octet rule.

6. **Conclusion**:
- Among the compounds analyzed, only PCl5 does not follow the octet rule as phosphorus has 10 electrons around it instead of 8.

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

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