Bonding of HCL and HF: Why Higher Boiling Temp for HF?

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Discussion Overview

The discussion focuses on explaining why hydrogen fluoride (HF) has a higher boiling temperature than hydrogen chloride (HCl), despite HF having a lower molecular weight. The scope includes concepts of molecular bonding, intermolecular forces, and comparisons with other compounds.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that the difference in boiling points is related to the bonding types, noting that higher boiling points require more thermal energy to separate molecules.
  • Another participant draws a parallel to the boiling point difference between water and methane, indicating that bonding plays a crucial role.
  • A participant proposes that intramolecular forces in HF and HCl are polar covalent, while the intermolecular forces in HCl are weak van der Waals forces, whereas HF exhibits hydrogen bonding.
  • One participant questions whether the higher electronegativity of fluorine compared to chlorine contributes to stronger van der Waals forces in HF.
  • A later reply affirms that the participant's reasoning about hydrogen bonding in HF is correct.
  • Another participant challenges the claim that HCl only has weak van der Waals forces, stating that there is significant hydrogen bonding in HCl as well.

Areas of Agreement / Disagreement

Participants express differing views on the nature and strength of intermolecular forces in HCl, with some asserting the presence of hydrogen bonding while others suggest it is primarily van der Waals forces. The discussion remains unresolved regarding the exact contributions of these forces to the boiling points of HF and HCl.

Contextual Notes

There are unresolved assumptions regarding the definitions and implications of intermolecular forces, particularly the nature of bonding in HCl and HF. The discussion does not clarify the extent to which hydrogen bonding influences boiling points compared to other factors.

Soilwork
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Homework Statement


Explain why hydrogen fluoride (HF) has a higher boiling temperature than hydrogen chloride (HCL) even though HF has a lower molecular weight.


Attempt
OK so from the looks of it I think that the bonding that bonds the H to the Cl and the H to the F is polar covalent. So why would it have the higher boiling point if it has a lower molecular weight?? I mean it must have something to do with bonding because a higher boiling point means that more thermal energy is required to separate the molecules.

Any help would be greatly appreciated.

Thanks
 
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The same rationale can be used to explain the difference in boiling point between water (MW = 18) and methane (MW = 16). Why the big difference in these two compounds of almost identical molecular weight?

I think you were on to it when you wrote, "I mean it must have something to do with bonding...".
 
Well I've been doing some reading and I think I might have it, but I'm not entirely sure. From the looks of it there are the intramolecular bonding forces and the intermolecular bonding forces. So the intramolecular forces are polar covalent because they are responsible for the bonding of the H to the Cl and the H to the F. However, the bonding forces between the various HCl molecules (intermolecular) are weak van der Waals forces. Then for HF we have hydrogen bonding which is stronger. Is this on the right track?
 
Doesn't F have a way higher electronegativity than Cl, implying that the van der Waals forces of attraction would be significantly greater?
 
Soilwork said:
Then for HF we have hydrogen bonding which is stronger. Is this on the right track?

Absolutely on the right track.
 
ahh cool. :)

Thanks!
 
Soilwork said:
However, the bonding forces between the various HCl molecules (intermolecular) are weak van der Waals forces.

This statement isn't quite right. There is significant hydrogen bonding in HCl.
 

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