bond polarity and acid strength
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bond polarity and acid strength
I understand that the higher the electronegativity of the anion in an acid, the more polarized the bond is, and therefore the stronger the acid but I am having trouble understanding why this is the case. What does a more positive partial charge an the H+ make it more likely to transfer a proton to H2O? Thanks!
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Re: bond polarity and acid strength
Hi there! I'm not sure I fully know how to address both of your questions, but I will do my best to at least answer the first part:
The more electronegative a certain atom is in a molecule, the more it draws on the electron density of the overall molecule. This pulling actually results in a higher stabilization state for the molecule. Therefore, the more electronegative a particular element is, the harder it pulls, and the more stable this molecule is.
Moreover, when you compare acids such as HCl, HF, HBr, and HI, acidity increases as electronegativity (and thus electron affinity) decreases. You can better visualize this if you look at the Periodic Table trends. A strong acid easily loses an H+ ion (the strongest acids almost completely dissociate in water, in fact), so the stronger acids must have a lower electron affinity. With regard to the acids HCl, HF, HBr, and HI, they just one atom besides H, so you can look at the bond length/strength to measure how acidic the acid is. The rule is that the stronger (shorter) the bond, the less likely it is to dissociate and the weaker the acid (thus, HF is the weakest acid in this list, and the order of their strength is HF > HCl > HBr > HI). However, when comparing acids that have more than H and one other atom, and the same type of atom is directly attached to the acidic proton, it is best to look at the stability of the conjugate base. If we compare HBrO2 to HClO2, for instance, we can say that while the O-H bond is broken in both, BrO2- is less stable. This is because Br is less electronegative than Cl, so the charge of BrO2- is less spread out than it is in ClO2-.
I hope this helps somewhat!
The more electronegative a certain atom is in a molecule, the more it draws on the electron density of the overall molecule. This pulling actually results in a higher stabilization state for the molecule. Therefore, the more electronegative a particular element is, the harder it pulls, and the more stable this molecule is.
Moreover, when you compare acids such as HCl, HF, HBr, and HI, acidity increases as electronegativity (and thus electron affinity) decreases. You can better visualize this if you look at the Periodic Table trends. A strong acid easily loses an H+ ion (the strongest acids almost completely dissociate in water, in fact), so the stronger acids must have a lower electron affinity. With regard to the acids HCl, HF, HBr, and HI, they just one atom besides H, so you can look at the bond length/strength to measure how acidic the acid is. The rule is that the stronger (shorter) the bond, the less likely it is to dissociate and the weaker the acid (thus, HF is the weakest acid in this list, and the order of their strength is HF > HCl > HBr > HI). However, when comparing acids that have more than H and one other atom, and the same type of atom is directly attached to the acidic proton, it is best to look at the stability of the conjugate base. If we compare HBrO2 to HClO2, for instance, we can say that while the O-H bond is broken in both, BrO2- is less stable. This is because Br is less electronegative than Cl, so the charge of BrO2- is less spread out than it is in ClO2-.
I hope this helps somewhat!
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