Rationalize why chalk (calcium carbonate) has a higher melting point than motor oil (large compound made from carbon and hydrogen), which has a higher melting point than water and engages in relatively strong hydrogen bonding interactions.

Intermolecular forces are forces of attraction or repulsion that exist between molecules. These forces can impact the properties of materials, including melting and boiling points. There are three primary types of intermolecular forces: London Dispersion Forces, Dipole-Dipole Interactions, and Hydrogen Bonding.

Calcium carbonate (CaCO3) is an ionic compound, which means that it consists of ions with opposite charges held to each other by strong electrostatic attractions called ionic bonds. In this case, there is a positively charged calcium ion (Ca^2+) and the negatively charged carbonate ion (CO3^2-). The ionic bonds within calcium carbonate require substantial energy to break, resulting in a higher melting point compared to non-ionic compounds.

Motor oil is primarily composed of large hydrocarbon chains (molecules containing mostly carbon and hydrogen). Hydrocarbons exhibit London Dispersion Forces, which are the weakest type of intermolecular force caused by temporary fluctuations in electron distribution. However, due to the large size of the molecules found in motor oil, these interactions are relatively strong compared to smaller hydrocarbon molecules. Geometrically, the long chains of hydrocarbons in motor oil can interact through the increased surface area, creating relatively strong London Dispersion Forces that contribute to a higher melting point than smaller hydrocarbon molecules.

Water (H2O) is a polar molecule, meaning that it has a net uneven distribution of electron density. This creates two regions with opposite charges – a positive end with the hydrogen atoms and a negative end with the oxygen atom. This arrangement results in strong intermolecular forces known as hydrogen bonds, which occur between the hydrogen atom of one water molecule and the oxygen atom of another. While hydrogen bonds are relatively strong compared to other intermolecular forces (such as London Dispersion Forces or Dipole-Dipole Interactions), they are still weaker than the ionic bonds present in calcium carbonate.

Now that we have evaluated the interactions in each substance, we can compare the melting points: 1. Calcium Carbonate (chalk) - Has ionic bonds, which are the strongest of the interactions discussed, requiring the most energy to break and therefore resulting in the highest melting point. 2. Motor Oil - Has relatively strong London Dispersion Forces due to the large hydrocarbon molecules and their increased surface area, which allows for more interactions and a higher melting point compared to water. 3. Water - Engages in hydrogen bonding, which, although relatively strong compared to other intermolecular forces, is weaker than ionic bonds, resulting in a lower melting point than calcium carbonate and motor oil. In conclusion, chalk (calcium carbonate) has the highest melting point due to the strong ionic bonds, followed by motor oil with its pronounced London Dispersion Forces, and finally water with its hydrogen bonding interactions.