We’re being asked to arrange the given compounds by their expected boiling points.
Recall that there are several types of intermolecular forces (IMF):
1. Ion-dipole interaction – occurs between an ion and a polar covalent compound; strongest IMF
2. Hydrogen bonding – occurs in compounds where hydrogen is directly connected to an electronegative element such as N, O, or F; 2nd strongest IMF
3. Dipole-dipole interaction – occurs between two polar covalent compounds; 3rd strongest IMF
4. Dispersion forces – occurs in all compounds and is the primary IMF exhibited by nonpolar compounds; weakest IMF
Compounds with strong intermolecular forces have high boiling points. This is because they require more energy to be able to break the bonds during the phase transition.
So, we need to identify the strongest intermolecular forces in each compound.
For CH3OH: The total number of valence electrons present in CH3OH is:
Group Valence Electrons
C 4A 1 × 4 e– = 4 e–
H 1A 4 × 1 e– = 4 e–
O 6A 1 × 6 e– = 6 e–
Total: 14 valence e–
The Lewis structure of CH3OH is:
Arrange these compounds by their expected boiling point
Highest to lowest boiling point
CH3OH, CH4, CH3Cl
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