Q 6. '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?

Q 6. '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?

Solution:–

Melting points of substances

Water = 273K

Ethyl alcohol = 155·7K

Diethyl ether = 156·8K

Methane        = 90·5K.

The stability of crystals depends up on the packing of the atoms. if there are strong force of attraction between the constituent particles then greater the stability.  

Water – strong intermolecular hydrogen bonding

Ethyl alcohol             – strong intermolecular hydrogen bonding.

Diethyl ether – it is a polar molecule so there is dipole –dipole attraction

Methane        – is  a non–polar molecule so that there is weak van der Waal's forces (London dispersion forces).