Why do molecules have low melting points?

• A. Weak intermolecular forces
• B. Strong covalent bonds
• C. High density
• D. Large molecular mass

Answer: (A)

Melting a solid of molecules happens when the forces holding the molecules in the solid lattice are overcome. If these intermolecular forces are weak, only a small amount of energy is needed to separate the molecules, so the substance melts at a low temperature. The bonds that typically define the strength of a solid of molecules are the weaker intermolecular forces (like London dispersion forces, dipole-dipole interactions, or hydrogen bonds), not the strong covalent bonds inside each molecule. Those covalent bonds stay intact during melting, so they don’t determine the melting point directly.

Density isn’t the deciding factor for melting point, and while larger molecules can experience stronger overall intermolecular forces, the key point is the strength of the forces between different molecules, not the mass or density.