Which of the substances in each of the following sets would...

Which of the substances in each of the following sets would be expected to have the lowest melting point? Explain why.
a. $\mathrm{H}_{2}, \mathrm{N}_{2}, \mathrm{O}_{2}$
b. $\mathrm{Xe}, \mathrm{NaCl}, \mathrm{C}$ (diamond)
c. $\mathrm{Cl}_{2}, \mathrm{Br}_{2}, \mathrm{I}_{2}$

Key Concepts

Intermolecular Forces

This concept explains the forces between molecules that determine how strongly they attract one another in the solid state. For nonpolar molecules, such as many simple gases and halogens, London dispersion forces are the key type of intermolecular attraction, and variations in these forces can lead to differences in melting points.

Molecular Weight and Polarizability

This concept highlights that molecular size and the ease with which their electron clouds can be distorted (polarizability) directly affect the strength of London dispersion forces. Generally, molecules with lower molecular weights exhibit weaker dispersion forces, resulting in lower melting points compared to their heavier counterparts.

Bonding Types

This concept covers the different types of chemical bonds—ionic, covalent, and network covalent—and their impact on melting points. Substances with ionic bonds or extensive covalent networks tend to have very high melting points, as breaking these bonds requires much more energy than overcoming the weaker van der Waals forces found in nonpolar molecules.

Crystal Lattice Structure and Lattice Energy

This concept involves understanding how the arrangement and interactions of particles in a crystal lattice influence its stability. A well-organized and strongly bound lattice, whether by ionic bonds or covalent networks, results in a high melting point, while a loosely packed lattice formed only by weak intermolecular forces leads to a lower melting point.

Transcript

Please give Ace some feedback