How does the atomic radius affect the strength of an acid?

1 Answer
May 26, 2018

Well, take the hydrogen halides....


#HF, HCl, HBr, HI#
#stackrelrarr"increasing acid strength"#

And we examine the reaction....

#HX(aq) + H_2O(l) rightleftharpoons H_3O^+ + X^-#

The stronger the acid, the farther to the right the equilibrium moves...

While entropy CERTAINLY influences the reaction (i.e. fluoride anion is entropically disfavoured), we could certainly point to the role of enthalpy in this reaction. The LARGER halides possess POORER orbital overlap with respect to the small hydrogen atom. And acidic strength INCREASES for the higher hydrogen halides.