increasing acidity  | ||||
| CH4 | NH3 | H2O | HF |  |
| H2S | HCl | |||
| weak acids | HBr | |||
| strong acids | HI | |||
decreasing basicity  | |||||
| H– | | ||||
| C4– | N3– | O2– | F– | ||
| S2– | Cl– | ||||
| strong base | Br– | ||||
| weak base | I– | ||||
The tendency of an acid to donate a proton to a base is referred to as its acid strength.
The acid strength of HnX can be correlated with the location of X in the periodic table.
As shown below, the acidity of HnX is higher for X farther to the right across a row and farther down a group the periodic table.
The trend in basicities of Xn– is the oppsite to the trend in acidity of EHn.
Excepting the halide ions, Xn– are strong bases.
Strong bases exist in aqueous solution as a mixture of a protonated form and OH–.
N3– and C4– are fully protonated.
N3– + 3H2O → NH3 + 3OH–
C4– + 4H2O → CH4 + 4OH–
S2– and O2– react with one water.
O2– + H2O → 2OH–
S2– + H2O → SH– + OH–
N3– + 3H2O → NH3 + 3OH–
C4– + 4H2O → CH4 + 4OH–
S2– and O2– react with one water.
O2– + H2O → 2OH–
S2– + H2O → SH– + OH–