Which one has the highest and lowest boiling point ?

Options

A. `H_2 O, H_2 S`
B. `H_2 O, H_2 Se`
C. `H_2 S, H_2 O`
D. `H_2 S, H_2 Se`

Answer

To determine which compound has the highest and lowest boiling points among the hydrides of group 16 elements (specifically H2S, H2Se, H2Te, and H2O), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Boiling Points**:
- Boiling points are influenced by the strength of intermolecular forces. Stronger intermolecular forces lead to higher boiling points.

2. **Types of Intermolecular Forces**:
- The main types of intermolecular forces include Van der Waals forces (dispersion forces) and hydrogen bonding. Hydrogen bonding is a particularly strong type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine.

3. **Analyzing the Compounds**:
- The compounds we are considering are:
- H2S (Hydrogen sulfide)
- H2Se (Hydrogen selenide)
- H2Te (Hydrogen telluride)
- H2O (Water)

4. **Comparing Molecular Weights**:
- As the molecular weight increases, the Van der Waals forces also increase, which generally leads to higher boiling points.
- The molecular weights are approximately:
- H2S: 34 g/mol
- H2Se: 80 g/mol
- H2Te: 130 g/mol
- H2O: 18 g/mol

5. **Identifying Hydrogen Bonding**:
- Water (H2O) exhibits strong hydrogen bonding due to the presence of oxygen, which is highly electronegative. This significantly increases its boiling point compared to the other hydrides.

6. **Ranking the Boiling Points**:
- Based on the strength of intermolecular forces and molecular weights, we can rank the boiling points:
- H2S has the lowest boiling point due to weaker Van der Waals forces and no hydrogen bonding.
- H2Se has a higher boiling point than H2S but lower than H2Te.
- H2Te has a higher boiling point than both H2S and H2Se due to its higher molecular weight.
- H2O has the highest boiling point due to strong hydrogen bonding.

7. **Conclusion**:
- Therefore, the compound with the highest boiling point is H2O (water), and the compound with the lowest boiling point is H2S (hydrogen sulfide).

### Final Answer:
- **Highest Boiling Point**: H2O (Water)
- **Lowest Boiling Point**: H2S (Hydrogen sulfide)