A common prank on college campuses is to switch the salt and sugar on dining hall tables, which is usually easy because the substances look so much alike. Yet, despite the similarity in their appearance, these two substances differ greatly in their properties, since one is a molecular solid and the other is an ionic solid. How do the properties differ and why?

Molecular solids are made up of molecules held together by weak intermolecular forces, like Van der Waals forces or hydrogen bonding. These forces are weaker than the covalent bonds that hold individual molecules together. Examples of molecular solids include sugar, dry ice (CO2), and most organic compounds. Ionic solids, on the other hand, are composed of positively charged ions (cations) and negatively charged ions (anions) held together by strong electrostatic forces (ionic bonding). These forces result from the interaction of particles that have opposite charges. One well-known example of an ionic solid is table salt (NaCl).

Molecular solids usually have the following properties: 1. Low melting and boiling points: Due to the weak intermolecular forces, molecular solids have low melting and boiling points compared to ionic solids. 2. Poor electrical conductivity: Molecular solids do not have free-moving charges, so they are weak conductors of electricity. 3. Generally soft and brittle: Molecular solids have a soft and brittle consistency due to the weak intermolecular forces. Ionic solids exhibit these properties: 1. High melting and boiling points: The strong electrostatic forces between the ions lead to high melting and boiling points. 2. Good electrical conductivity when dissolved or melted: While ionic solids are poor conductors in their solid state, when dissolved in water or melted, the ions become free to move and conduct an electric current. 3. Hard and brittle: Ionic solids tend to be harder than molecular solids because of the strong ionic bonding, and they can be quite brittle.

- Melting and boiling points: Sugar, being a molecular solid, has a lower melting point than salt, which is an ionic solid. This is the main reason why sugar dissolves faster in water than salt. - Electrical conductivity: Both sugar and salt are poor conductors of electricity in their solid states, but salt conducts electricity when dissolved in water or melted. - Hardness and brittleness: While both sugar and salt are brittle, salt is generally harder than sugar due to the stronger ionic bonding present. In conclusion, sugar (a molecular solid) and salt (an ionic solid) have different properties due to the types of forces that hold their structures together - weak intermolecular forces in molecular solids and strong ionic bonds in ionic solids.