[seal308]

This comes from my textbook
"Breaking the H — X bond becomes easier to accomplish as the bond energy becomes smaller or as the bonding electrons become less polarized toward X. "

i understand the bond energy part. (going down a group acidity level increases)

however i don't get "as the bond electrons become less polarized toward X"
I thought the more the electrons are polarized towards X. the easier it would be for the H to be broken of the compound. This would explain why going right in a row increases acidity (b/c electronegativity difference increases making the compound more polar)
So shouldn't be more not less?

Another question
I'm getting confused in my textbook it says HCl is a stronger acid than HBr b/c it has a higher electronegativity.
At the same time it says that HSe is stronger than HS b/c  it has a higher principal quantum number neaning H-S is a weaker bond
but how does this make sense. Br is below Cl in the periodic table just like how Se is be S but they act differently.
Also HBrO is a weaker acid than HBr. I thought the more oxygen you have the more the electron density goes towards the oxygen increasing acidity.
Why is this hapenning?

[Sophia7X]

I'm getting confused in my textbook it says HCl is a stronger acid than HBr b/c it has a higher electronegativity.

What book is that?

HCl isn't stronger than HBr. HBr is stronger because Br is bigger, thus having a better ability to stabilize charge. HBr's pKa is -8.7 while HCl is -6.3, so HBr is more acidic since it has a more negative pKa.


What atom the H is bonded to: If in the same row on the periodic table, the one with the more electronegative atom is stronger. However, when comparing atoms in the same group, size is the determining factor. HBr is stronger than HCl, and HI is stronger than HBr because I is the largest, then Br, then Cl being the smallest. This is why HF is a weak acid; despite F being very electronegative, it is extremely small so it cannot stabilize charge as well as HCl, HBr, or HI.

Big atoms can stabilize charge better than small atoms simply because there is more space to spread that charge out. Again, this is when you're comparing two acids, in which the atoms bonded to H is in the same group.

An acid is strong if the negative charge of the conjugate base is stable because then the acid will be more willing to give up H+.

[Borek]

HBr's pKa is -8.7 while HCl is -6.3

Don't treat these values too seriously - different (serious) sources give different values.

[seal308]

thanks sophia.
I knew it looked odd.