Acid/Base Trends

[DTingey_1C]

If the strength of binary acids increases with elements across a period because of the increase in electronegativity, why does the strength of binary acids also increase with elements down a group if electronegativity typically decreases down a group? Thanks

[Veronica_Lubera_2A]

Strong acids dissociate completely. When going down a group, the atoms are getting larger (making a bond longer), and therefore making the bond weaker. Therefore, the strength will increase because the bond is easier to break.

[Rita Chen 1B]

I think this is because as you go down a group for binary acids, you are looking at the strength and length of the HA bond, not the polarity, so the weaker the HA bond, the stronger the acid.

[Annie Ye]

Why is HF a weaker acid than HI?

[Daniel Honeychurch1C]

I has a larger ionic radius which makes the H-I bond longer and weaker. Therefore, HI dissociates more than HF and is a stronger acid.

[andrewcj 2C]

Why is HF a weaker acid than HI?

When an acid dissociates, the bond must be broken between the H⁺ and the conjugate base. If the bond is strong, which it is in the case of HF, this makes it harder and less of the acid dissociates, resulting in less H⁺ present in the resulting solution and a higher pH by definition of pH.

[Annie Ye]

The trend of acidity increases from left to right across the periodic table but it decreases going from top to bottom.