Although the H-bonding in hydrogen fluoride is much stronger than that in water, yet water has a much higher boiling point than hydrogen fluoride. Why?

Answer

To understand why water (H₂O) has a higher boiling point than hydrogen fluoride (HF) despite HF having stronger hydrogen bonding, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Understanding Hydrogen Bonding**:
- Hydrogen bonding occurs when a hydrogen atom covalently bonded to a highly electronegative atom (like F, O, or N) interacts with another electronegative atom. In HF, the hydrogen bonds are strong due to the high electronegativity of fluorine.

**Hint**: Recall that hydrogen bonds are stronger when the hydrogen is bonded to highly electronegative atoms.

2. **Comparing the Strength of Hydrogen Bonds**:
- While HF has stronger hydrogen bonds than water due to the presence of fluorine, the overall effect on boiling point is not solely dependent on bond strength.

**Hint**: Consider both the strength and the arrangement of hydrogen bonds in the molecules.

3. **Molecular Structure and Geometry**:
- Water has a bent molecular geometry due to its two lone pairs on oxygen, which allows for more complex hydrogen bonding interactions. Water molecules can form multiple hydrogen bonds with neighboring molecules, creating a three-dimensional network.

**Hint**: Visualize the molecular geometry of water and HF to understand how they interact with each other.

4. **Dimensionality of Hydrogen Bonding**:
- The hydrogen bonding in water is multidimensional, meaning that each water molecule can participate in multiple hydrogen bonds at once, leading to a more extensive network. In contrast, HF has a more linear arrangement, limiting the number of hydrogen bonds that can form.

**Hint**: Think about how the arrangement of molecules affects the overall structure and stability of the liquid.

5. **Impact on Boiling Point**:
- The extensive hydrogen bonding network in water requires more energy (in the form of heat) to break these interactions when transitioning from liquid to gas, resulting in a higher boiling point. In contrast, the linear hydrogen bonding in HF does not create as strong a network, leading to a lower boiling point.

**Hint**: Relate the strength and number of hydrogen bonds to the energy required to change states from liquid to gas.

### Conclusion:
In summary, although hydrogen fluoride has stronger hydrogen bonds, the multidimensional hydrogen bonding in water leads to a more stable and higher energy state, resulting in a higher boiling point for water compared to hydrogen fluoride.