Which type of intermolecular force is primarily responsible for the interaction between molecules in a liquid and molecules in a solid during melting?

• A. London dispersion forces
• B. Covalent bonding
• C. Hydrogen bonding
• D. Ionic bonding

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the nature of intermolecular forces and intramolecular forces. Intermolecular forces are forces between molecules, while intramolecular forces (like covalent and ionic bonds) hold atoms together within a molecule or compound.
2. Step 2: Recognize that melting involves a phase change from solid to liquid, where molecules overcome some intermolecular forces to move more freely but the molecules themselves remain intact (no breaking of covalent or ionic bonds).
3. Step 3: Identify the types of intermolecular forces: London dispersion forces, dipole-dipole interactions, and hydrogen bonding. Covalent and ionic bonding are intramolecular forces and not responsible for interactions between separate molecules during melting.
4. Step 4: Consider that London dispersion forces are present in all molecules, especially nonpolar ones, and are often the primary force in molecular solids and liquids where no strong dipole or hydrogen bonding exists.
5. Step 5: Conclude that during melting, the primary intermolecular force being overcome between molecules in the solid and liquid phases is the London dispersion force, as it is the weakest and most universal intermolecular force responsible for holding molecules together in many molecular solids.