Question

select the arrangement that orders the compounds by increasing boiling point based on predominant intermolecular force.

\\(\text{ch}_4 < \text{br}_2 < \text{hcl} < \text{nh}_3\\)
\\(\text{nh}_3 < \text{hcl} < \text{br}_2 < \text{ch}_4\\)
\\(\text{br}_2 < \text{ch}_4 < \text{hcl} < \text{nh}_3\\)
\\(\text{ch}_4 < \text{br}_2 < \text{nh}_3 < \text{hcl}\\)

Explanation:

Identify predominant intermolecular forces

• \(\text{CH}_4\): Nonpolar molecule, predominant force is London dispersion forces (weakest).
• \(\text{Br}_2\): Nonpolar molecule, predominant force is London dispersion forces. However, because it has a much larger electron cloud than \(\text{CH}_4\), its dispersion forces are stronger, but the question specifies ordering "based on predominant intermolecular force" type.
• \(\text{HCl}\): Polar molecule, predominant force is dipole-dipole interactions (moderate).
• \(\text{NH}_3\): Polar molecule with \(\text{N-H}\) bonds, predominant force is hydrogen bonding (strongest).

Order by increasing strength of predominant force

• London dispersion forces < Dipole-dipole interactions < Hydrogen bonding.
• This yields the sequence: \(\text{CH}_4 < \text{Br}_2 < \text{HCl} < \text{NH}_3\).

Answer:

• (A) \(\text{CH}_4 < \text{Br}_2 < \text{HCl} < \text{NH}_3\) (Correct answer)
• (B) \(\text{NH}_3 < \text{HCl} < \text{Br}_2 < \text{CH}_4\)
• (C) \(\text{Br}_2 < \text{CH}_4 < \text{HCl} < \text{NH}_3\)
• (D) \(\text{CH}_4 < \text{Br}_2 < \text{NH}_3 < \text{HCl}\)