Q. 1.6    '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?

Answers (1)
D Devendra Khairwa

If a crystal has a high melting point implies that it will require high temperature or say energy to break the intermolecular bonds. Also if the intermolecular forces are strong then the crystal is more stable. Thus it can be said that higher the melting point high is the stability.

Melting points of compounds are given below:- 

(i) Water:- 273 K

(ii) Ethyl alcohol:- 155.7 K

(iii) Diethyl ether:- 156.8 K

(iv) Methane:-  90.5 K

It can be concluded from the above data that among all, the intermolecular force of attraction is highest in water and lowest in methane. The possible reason for this is the hydrogen bonding present in water whereas the Vanderwall force of attraction is present in case of methane.