In the given alkyl halides which one has minimum boiling point?

Options

A. `C_(2)H_(5)F`
B. `C_(2)H_(5)I`
C. `C_(2)H_(5)Cl`
D. `C_(2)H_(5)Br`

Answer

To determine which alkyl halide has the minimum boiling point among the given options, we will analyze the factors affecting boiling points in alkyl halides.

### Step-by-Step Solution:

1. **Understanding Boiling Point Dependence**:
- The boiling point of a compound is influenced by the intermolecular forces present. In the case of alkyl halides, the primary forces are Van der Waals forces (dispersion forces).
- Generally, a higher boiling point corresponds to stronger intermolecular forces.

2. **Factors Affecting Boiling Point**:
- The boiling point is influenced by two main factors:
- **Molar Mass**: Higher molar mass typically leads to stronger Van der Waals forces due to increased electron cloud size, resulting in a higher boiling point.
- **Surface Area**: A larger surface area can also lead to stronger Van der Waals forces, contributing to a higher boiling point.

3. **Analyzing the Given Alkyl Halides**:
- Consider the alkyl halides: C2H5F (ethyl fluoride), C2H5Cl (ethyl chloride), C2H5Br (ethyl bromide), and C2H5I (ethyl iodide).
- The common alkyl group (C2H5) has a fixed mass, so we will focus on the halogen atoms.

4. **Calculating Molar Mass of Each Alkyl Halide**:
- For each halide, we will add the molar mass of the halogen to the fixed mass of the ethyl group (C2H5):
- C2H5F: Molar mass = 29 (C2H5) + 19 (F) = 48 g/mol
- C2H5Cl: Molar mass = 29 (C2H5) + 35.5 (Cl) = 64.5 g/mol
- C2H5Br: Molar mass = 29 (C2H5) + 80 (Br) = 109 g/mol
- C2H5I: Molar mass = 29 (C2H5) + 127 (I) = 156 g/mol

5. **Comparing Molar Masses**:
- The calculated molar masses are:
- C2H5F: 48 g/mol
- C2H5Cl: 64.5 g/mol
- C2H5Br: 109 g/mol
- C2H5I: 156 g/mol
- The lowest molar mass is for C2H5F.

6. **Conclusion**:
- Since C2H5F has the lowest molar mass, it will have the weakest Van der Waals forces among the given alkyl halides, resulting in the lowest boiling point.
- Therefore, the alkyl halide with the minimum boiling point is **C2H5F (ethyl fluoride)**.