My chemistry teacher mentioned that the acidity of HX compounds increases down the group (i.e. HF<HCl<HBr<HI), and I get why it is so (because the atomic radius of the atom increases down the group => bond length increases => less attraction between H⁺ and X^- => donates H⁺ more readily).
But whenever I search for strong acids online, they only mention HF and HCl, while HI is very much stronger than those acids. Why is it like that? Is it just because they are more well known? Or is there another reason?

1 hour ago, heiwuchang said:

My chemistry teacher mentioned that the acidity of HX compounds increases down the group (i.e. HF<HCl<HBr<HI), and I get why it is so (because the atomic radius of the atom increases down the group => bond length increases => less attraction between H⁺ and X^- => donates H⁺ more readily).
But whenever I search for strong acids online, they only mention HF and HCl, while HI is very much stronger than those acids. Why is it like that? Is it just because they are more well known? Or is there another reason?

I'm sure you can find information about HBr and HI. There is a more detailed comparison of the relative strength of acidity of the hydrogen halides here: https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_17%3A_The_Halogens/1Group_17%3A_General_Reactions/The_Acidity_of_the_Hydrogen_Halides

A lot of this is taken up with explaining why HF is a weak acid, due to the special effects of hydrogen bonding, which is lost when it ionises, and the negative entropy change on solvation. So there is an argument for treating HF as the odd one out.

But you will also find a table of pKa values comparing HF, HCl, HBr and HI which indeed increase as you go down the group.  

(P.S. In spite of being only a weak acid, HF is highly dangerous as it burns skin and flesh and can penetrate down to the bone, causing serious damage.)