a. "Stability of a crystal is reflected in the magnitude of its melting points" Comment.
b. Melting points of some compounds are given below water `= 273 K`, ethyl alcohol `= 153.7 K`, diethyl ether `= 156.8 K`, methane `= 90.5 K`. What can you say about the intermolecular forces between the molecules of these compounds?

Explanation

Ionic compounds have high melting points. There is a strong force of attraction between the oppositely charged ions, so a lot of heat energy is required to break this force of attraction and have high melting points. The force of attraction between the molecules of a covalent compound is very weak. Only a small amount of heat energy is required to brea these weak molecular forces, due to which covalent compounds have low melting points.
b. i. The intermolecular forces in `H_(2) O` and `C_(2) H_(5) OH` an H-bonding. Higherr melting points of `H_(2) O` than `C_(2) H_(5) OH` shows that H-bonding in `H_(2) O` molecules is stronger than `C_(2) H_(5) OH` molecules.
ii. Diethyl ether is a polar molucule. The intermolecular forces ar dipole-attarction.
iii. `CH_(4)` is non-polar molecular having weak van der waal's forces (London dispersion forces).