Why is HF Not a Lewis Base and MgBr2 a Lewis Acid?

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Discussion Overview

The discussion revolves around the classification of HF (hydrofluoric acid) and MgBr2 (magnesium bromide) in terms of Lewis acid-base theory. Participants explore why HF is not considered a Lewis base and the reasoning behind MgBr2 being classified as a Lewis acid, examining various contexts and interactions.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions why HF is not a Lewis base, suggesting that the presence of lone pairs on F- could allow for electron donation.
  • Another participant argues that the high electronegativity of fluorine leads to a dipole moment, which affects the behavior of HF, implying that it does not act as a Lewis base due to the strong bond with hydrogen.
  • A different perspective is introduced, stating that HF can act as a Lewis base in specific contexts, such as intermolecular hydrogen bonding, and can also act as a Lewis acid depending on the reaction conditions.
  • It is noted that in aqueous solutions, HF behaves as a stronger acid, indicating that the classification may depend on the specific chemical environment.

Areas of Agreement / Disagreement

Participants express differing views on the classification of HF and MgBr2, with no consensus reached on whether HF can act as a Lewis base or the conditions under which it does so.

Contextual Notes

The discussion highlights the importance of context in determining the behavior of HF and MgBr2, suggesting that definitions and classifications may vary based on specific interactions and conditions.

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why's HF not a lewis base? doesn't F- have lone pairs which could be used to donate electrons?
why's MgBr2 a Lewis acid and not a lewis base?
 
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well to start with, since F has three lone pairs, it would seem to be a good explanation, except that it is so electronegative that most of the time, electron of hydrogen are with F instead, giving it a dipole moment. A Lewis acid is when it can accept electrons or donate protons, in this case it could do that because hydrogen is just hanging there barely (F is so negative that the hydrogen bond can easily break).
 
Depends on what context you're referring to. HF can act as a lewis base, when it participates in intermolecular hydrogen bonding (and a lewis acid in this case). The LUMO on the hydrogen will interact with the HOMO on the Flourine.

In aqueous solutions, and in the case of its reaction with water, it's an acid, that is the stronger acid.

In either case you've got to consider what the compound is reacting with.
 
thank you very much! ^^
 

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