Question

LiI has lower melting point than LiF. Why ?

Answer 1

liI is covalent.liF is ionic.so generally ionic compound having high mp and bp

Answer 2

Explanation:

According to Fajan's rule, the smaller is the cation and larger is the anion then more will be the polarizing power of cation and easily the anion will get distorted.

As a result, a covalent bond will form between the two atoms.

In case of LiI (lithium iodide), there will be a covalent bond between Li and I as Li is smaller in size and I is much larger in size. Therfore, iodine will easily get distorted.

Whereas the bonding between LiF will be ionic because both Li and F are small in size. As a result, they will be closely held to each other so there will be strong forces of attraction due to the opposite charges and small size that they have.

Hence, to break this ionic bond more heat has to be supplied. Thus, LiF will have high melting point as compared to LiI or vice versa.