Why Doesn't Table Salt Melt Easily?

Table salt, which is sodium chloride, is an ionic compound. The attractive forces between the positive and negative ions in ionic compounds are strong and require a large amounts of energy to break. This means that a high temperature is needed to melt table salt.

The melting point of a compound is explained by its enthalpy of fusion, which is the amount of heat energy required to melt one mole of a compound kept at constant pressure. The higher the enthalpy of fusion for a compound, the higher its boiling point.

Ionic compounds have higher enthalpies of fusion than molecular compounds, which have covalent bonds instead of ionic bonds. Ions are atoms that either donate or receive valence electrons. They bond through strong attractive forces unlike covalently bonded molecules, such as water, that share electrons. These attractive forces are what give ionic compounds their distinct properties, such as high melting and boiling points.

Just like the enthalpy of fusion can explain a compound's melting point, the enthalpy of vaporization can explain a compound's boiling point. Following the same concept and thermodynamic principles, the enthalpy of vaporization denotes how much energy is required to vaporize one mole of a compound under constant pressure.