To determine why HF (hydrogen fluoride) has the highest boiling point among the hydrogen halides (HF, HCl, HBr, HI), we can analyze the intermolecular forces present in each compound.
### Step-by-Step Solution:
1. **Identify the Hydrogen Halides**:
The hydrogen halides we are considering are HF, HCl, HBr, and HI.
2. **Understand Intermolecular Forces**:
The boiling point of a substance is influenced by the strength of its intermolecular forces. The stronger the intermolecular forces, the higher the boiling point.
3. **Types of Intermolecular Forces**:
- **Van der Waals Forces (London Dispersion Forces)**: These are weak forces present in all molecules, but they are the only forces in non-polar molecules.
- **Dipole-Dipole Interactions**: Present in polar molecules, these forces are stronger than Van der Waals forces.
- **Hydrogen Bonding**: A specific type of strong dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like fluorine, oxygen, or nitrogen.
4. **Analyze HF**:
- HF exhibits strong hydrogen bonding due to the high electronegativity of fluorine. The bond between hydrogen and fluorine creates a significant dipole, leading to strong hydrogen bonds between HF molecules.
5. **Analyze Other Hydrogen Halides**:
- HCl, HBr, and HI do not exhibit hydrogen bonding to the same extent as HF. While they have dipole-dipole interactions, they are weaker compared to the hydrogen bonds in HF.
- The boiling points of HCl, HBr, and HI are influenced mainly by Van der Waals forces, which are weaker than hydrogen bonds.
6. **Conclusion**:
- Since HF has strong hydrogen bonding, it has a higher boiling point compared to HCl, HBr, and HI, which rely on weaker intermolecular forces.
7. **Final Answer**:
- The reason HF has the highest boiling point among hydrogen halides is due to the presence of **strongest hydrogen bonding**.
