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Why is MELTING POINT of HF less than HI ..???????plzzzzz justify....

Why is MELTING POINT of HF less than HI ..???????plzzzzz justify....

Grade:12th pass

2 Answers

Arun
25750 Points
5 years ago
Although HI has a higher molecular mass than HF, the Van Der Waal's forces of attraction in HI are overpowered by intermolecular hydrogen bonding in HF. Hence, HFhas a lower melting point than HI.
Rajdeep
231 Points
5 years ago
HELLO THERE!
 
There are two points which you must keep in your mind:
 
(i) Fluorine, Oxygen and Nitrogen (F, O, N): these three elements can form Hydrogen bonding, which increases the strength of the bond and thus, the melting point (as higher energy is required to break the bond and hence melt the compound).
 
(ii) Larger is the size of anion, greater is the surface area and hence, greater is the London Dispersion Forces (or Vander Waal’s Forces) acting on it.
 
 
In case of HF and HI:
=> There is inter-molecular Hydrogen bonding in HF.
=> There is greater Vander Waal’s forces in HI.
 
However, the size of I- is far greater than that of F-. Thus, the Vander waal’s forces in HI is stronger than the inter-molecular H-bonding in HF.
So comparatively more amount of energy is required to break the HI bond than the HF bond.
 
Thus, melting point of HF is less than the melting point of HI.
 
THANKS!

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