Question

What is the predominant intermolecular force in the liquid state of each of these compounds: ammonia (nh3), carbon tetrachloride (ccl4), and hydrogen chloride (hcl)?

Answer 1

• NH₃: Hydrogen bonds;
• CCl₄: London Dispersion Forces; (a.k.a. Induced dipole)
• HCl: Dipole-dipole Interactions.

Explanation

Relative strength of intermolecular forces in small molecules:

Hydrogen bonds > Dipole-dipole interactions > London DIspersion Forces.

It takes two conditions for molecules in a substance to form hydrogen bonds.

• They shall contain at least one of the three bonds: H-F, O-H, or N-H.
• They shall contain at least one lone pair of electrons.

NH₃ contains N-H bonds. The central nitrogen atom in an NH₃ molecule has one lone pair of electrons. NH₃ meets both conditions; it is capable of forming hydrogen bonds.

CCl₄ molecules are nonpolar. The molecule has a tetrahedral geometry. Dipole from the polar C-Cl bonds cancel out due to symmetry. The molecule is nonpolar overall. As a result, only London Dispersion Force is possible between CCl₄ molecules.

HCl molecules are polar. The H-Cl bond is fairly polar. The HCl molecule is asymmetric, such that the dipole won't cancel out. The molecule is overall polar. Both dipole-dipole interactions and London Dispersion Force are possible between HCl molecules. However, dipole-dipole interactions are most predominant among the two.