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

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SUMMARY

HF is not classified as a Lewis base due to the high electronegativity of fluorine, which causes the hydrogen atom to be less available for electron donation. Instead, HF can act as a Lewis acid in specific contexts, such as intermolecular hydrogen bonding. Conversely, MgBr2 is identified as a Lewis acid because it can accept electrons or donate protons, particularly in reactions where the context of the reacting compounds is crucial. The interaction between the LUMO of hydrogen and the HOMO of fluorine further illustrates the complexity of these classifications.

PREREQUISITES
  • Understanding of Lewis acid-base theory
  • Knowledge of electronegativity and its effects on molecular behavior
  • Familiarity with molecular orbital theory, specifically LUMO and HOMO concepts
  • Basic principles of hydrogen bonding in chemistry
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  • Research the role of electronegativity in Lewis acid-base reactions
  • Study molecular orbital theory, focusing on LUMO and HOMO interactions
  • Explore examples of Lewis acids and bases in various chemical reactions
  • Investigate the behavior of HF in different solvent systems, particularly aqueous solutions
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Chemistry students, educators, and professionals interested in acid-base theory and molecular interactions, particularly those focusing on Lewis acid-base classifications.

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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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