Which of the following would have a permanent dipole moment ?

Options

A. `BF_(3)`
B. `SiF_(4)`
C. `SF_(4)`
D. `XeF_(4)`

Answer

To determine which of the given compounds has a permanent dipole moment, we need to analyze the molecular geometry and the electronegativity differences between the atoms in each compound. A permanent dipole moment occurs when there is an uneven distribution of electron density due to differences in electronegativity, resulting in partial positive and negative charges within the molecule.

### Step-by-Step Solution:

1. **Understanding Dipole Moment**:
- A dipole moment arises when there is a difference in electronegativity between two bonded atoms, leading to an uneven distribution of electron density. The more electronegative atom attracts the shared electrons more strongly, resulting in a partial negative charge (δ-) on that atom and a partial positive charge (δ+) on the less electronegative atom.

2. **Analyzing Each Compound**:
- **Boron Trifluoride (BF3)**:
- Boron (B) has a lower electronegativity than fluorine (F). However, the molecule is symmetric (trigonal planar), and the dipoles from each B-F bond cancel out. Thus, BF3 has no permanent dipole moment.

- **Silicon Tetrafluoride (SiF4)**:
- Similar to BF3, silicon (Si) is less electronegative than fluorine (F), and SiF4 is also symmetric (tetrahedral). The dipoles cancel out, resulting in no permanent dipole moment.

- **Sulfur Tetrafluoride (SF4)**:
- Sulfur (S) is less electronegative than fluorine (F). SF4 has a seesaw shape due to the presence of one lone pair on sulfur. The asymmetrical arrangement leads to an unequal distribution of charge, resulting in a permanent dipole moment.

- **Xenon Tetrafluoride (XeF4)**:
- Xenon (Xe) is a noble gas and has a complete octet. XeF4 is square planar, and the dipoles from the four F atoms cancel out due to symmetry, resulting in no permanent dipole moment.

3. **Conclusion**:
- Among the compounds analyzed, only **SF4** has a permanent dipole moment due to its asymmetrical shape and the electronegativity difference between sulfur and fluorine.

### Final Answer:
The compound that has a permanent dipole moment is **SF4**.

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