Tuesday, January 17, 2017

inorganic chemistry - How to compare the boiling point of water, ammonia and hydrogen fluoride?


According to the values of boiling points that I found on internet the order is as follows:



$\ce{H2O}$ > $\ce{HF}$ > $\ce{NH3}$




I was expecting $\ce{HF}$ to have highest boiling point because F is the most electronegative atom hence should form stronger H Bonds.


Now, I think the factor here might be number of H Bond rather than strength of H Bond.




  • $\ce{H2O}$ have 2 lone pair and 2 H atoms, hence it can form 4 H Bonds with surrounding molecules.




  • Similarly $\ce{NH3}$ is also capable of forming 4 H Bonds with surrounding molecules.





  • $\ce{HF}$ on the other hand is only capable of forming 2 H Bonds with surrounding molecules.




Still the above hypothesis doesn’t explain why the boiling point of $\ce{HF}$ is greater than $\ce{NH3}$. I’m not sure what am I missing here.




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