Which of the following substances exhibits strong hydrogen...

Which of the following substances exhibits strong hydrogen bonding in the liquid and solid states?
(a) $\mathrm{CH}_{3} \mathrm{OH}$ (methanol); (b) $\mathrm{PH}_{3}$; (c) $\mathrm{CH}_{4}$;
(d) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH} ;$
(e) $\mathrm{CH}_{3} \mathrm{NH}_{2}$

Key Concepts

Hydrogen Bonding

Hydrogen bonding is a form of strong intermolecular attraction that occurs when a hydrogen atom covalently bonded to a highly electronegative atom (usually oxygen, nitrogen, or fluorine) interacts with a lone pair of electrons on another electronegative atom. This interaction significantly influences the physical properties of substances, such as their boiling and melting points, by enhancing attractions between molecules in both liquid and solid states.

Intermolecular Forces

Intermolecular forces are the attractive forces between molecules that determine many macroscopic properties like phase, viscosity, and boiling points. Among these forces, hydrogen bonds are notably strong compared to dispersion forces or typical dipole-dipole interactions, particularly when highly polar bonds are involved.

Electronegativity and Bond Polarity

Electronegativity is the measure of an atom’s ability to attract shared electrons in a chemical bond. When hydrogen is bound to highly electronegative atoms (like oxygen or nitrogen), the resulting bond is highly polar, leading to a partial positive charge on hydrogen and making it capable of forming strong hydrogen bonds with lone-pair electrons on other electronegative atoms.

Functional Groups and Molecular Structure

Specific functional groups, such as the hydroxyl (-OH) and amino (-NH or -NH2) groups, provide the necessary elements for hydrogen bonding by featuring hydrogen atoms bonded to electronegative atoms. The presence, number, and position of these groups in a molecule, as well as the overall molecular geometry, are crucial for determining the substance’s ability to form extensive hydrogen-bond networks in the liquid and solid states.

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