Question

‘Stability of a crystal is reflected in the magnitude of its melting points.’ Comment. Collect melting points of solid water, ethyl alcohol, diethyl ether and methane from a data book. What can you say about the intermolecular forces between these molecules?

Answer 1

The stability of the crystal increases with its melting point. This is due to the fact that the strength of the intermolecular interactions that hold particles together is correlated with a crystal’s melting point. The intermolecular forces are greater and the crystal is more stable when the melting point is higher.

The melting points of the given substances are as follows:

Solid water = 273 K

Ethyl alcohol = 155.7 K

Diethyl ether = 156.85 K

Methane = 90.5 K

We can infer from the aforementioned statistics that the substances intermolecular force magnitudes follow the following sequence.

Solid water > Diethyl ether > Ethyl alcohol > Methane

Intermolecular forces are strongest in solid water. The existence of hydrogen bonds is the cause of this. Hydrogen bonds are also present in ethyl alcohol, albeit to a smaller degree. Dipole-dipole interactions are the intermolecular forces seen in diethyl ether, a polar molecule. The weakest van der Waals forces, or intermolecular forces, are found in methane. This is due to the non-polar structure of the methane molecule.