At room temperature, common table salt (sodium chloride, or NaCl) is a solid. At the same temperature, however, methane (` `) is a gas. Explain, in terms of the bonds present in each compound, why their physical states are so different.
The chemicals that make up table salt and methane form different intermolecular bonds. These are the bonds between molecules in a substance. Let's look at the intermolecular bonds formed by each compound.
NaCl's intermolecular forces are ionic. These are very strong intermolecular forces, and they occur due to the big difference in their charge. They are opposite in charge (sodium is positive, chlorine is negative) and so they pull together strongly.
Methane, by contrast, is subject to only very weak London dispersion forces between its molecules. Carbon and hydrogen, the two elements that make up methane, are very close in electronegativity. That is, they are not at all opposite in charge. London dispersion forces are a weak intermolecular bond that every compound is subject to.
Ionic bonds take much more energy to break. This also means that substances made up of chemicals with ionic bonds have a higher melting point and boiling point than substances with ionic bonds. That is, the temperature at which they melt (turn from solid to liquid) and boil (turn from liquid to gas) is higher. This means that at room temperature, table salt is a solid, but methane is a gas because its boiling point is much lower.