It is very important to realize that
hydrogen attached to
- trivalent nitrogen (nitrogen bonded to three atoms) is NOT acidic in water.
- carbon is NOT acidic in water.
Hence compounds like NH3 and CH3NH2 are NOT referred to as acids.
Hydrogen attached to elements which are to the right and below oxygen (Group 16 Row 2) in the periodic table is acidic to varying degrees in water.
H–SH (Group 16 Row 3) and H–F (Group 17 Row 2) are weak acids.
H–Cl, H–Br or H–I (Group 17, Rows 3, 4 and 5) are strong acids.
With the exception of the monatomic anions from Group 17 elements, the monatomic anions from p-block elements are such strong bases that they do not exist in water (they react to give their protonated forms).
The most important example of this is O2– which is converted completely into OH- in aqueous solution.