Which of the following molecules does not contain a lone pair of electrons?

Options

A. `NH_(3)`
B. `PF_(5)`
C. `H_(2)O`
D. `SF_(4)`

Answer

To determine which molecule does not contain a lone pair of electrons, we will analyze each option by drawing their Lewis structures.

### Step 1: Analyze NH3 (Ammonia)
- **Valence Electrons**: Nitrogen (N) has 5 valence electrons, and each Hydrogen (H) has 1 valence electron. Therefore, NH3 has a total of \(5 + 3(1) = 8\) valence electrons.
- **Lewis Structure**: Nitrogen forms three single bonds with three Hydrogens, using 6 electrons (3 bonds). This leaves 2 electrons as a lone pair on Nitrogen.
- **Conclusion**: NH3 contains a lone pair of electrons.

### Step 2: Analyze PF5 (Phosphorus Pentafluoride)
- **Valence Electrons**: Phosphorus (P) has 5 valence electrons, and each Fluorine (F) has 7 valence electrons. Therefore, PF5 has a total of \(5 + 5(7) = 40\) valence electrons.
- **Lewis Structure**: Phosphorus forms five single bonds with five Fluorines, using all 5 of its valence electrons. There are no remaining electrons for a lone pair.
- **Conclusion**: PF5 does not contain a lone pair of electrons.

### Step 3: Analyze H2O (Water)
- **Valence Electrons**: Oxygen (O) has 6 valence electrons, and each Hydrogen has 1 valence electron. Therefore, H2O has a total of \(6 + 2(1) = 8\) valence electrons.
- **Lewis Structure**: Oxygen forms two single bonds with two Hydrogens, using 4 electrons. This leaves 4 electrons as 2 lone pairs on Oxygen.
- **Conclusion**: H2O contains lone pairs of electrons.

### Step 4: Analyze SF4 (Sulfur Tetrafluoride)
- **Valence Electrons**: Sulfur (S) has 6 valence electrons, and each Fluorine has 7 valence electrons. Therefore, SF4 has a total of \(6 + 4(7) = 34\) valence electrons.
- **Lewis Structure**: Sulfur forms four single bonds with four Fluorines, using 8 electrons. This leaves 2 electrons as one lone pair on Sulfur.
- **Conclusion**: SF4 contains a lone pair of electrons.

### Final Conclusion
From the analysis, the molecule that does not contain a lone pair of electrons is **PF5** (option B).

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