The simplest molecular acids are HnX where element X is more electronegative than H.
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. The acidity of HnX is higher for X farther to the right across a row and farther down a group the periodic table.
Strong acids react with water to the extent (extent of conversion of reactants to products - often expressed as a percentage) of 100%
Weak acids react with water to the extent (extent of conversion of reactants to products - often expressed as a percentage) of less than 5%.
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.
increasing acidity  | ||||
| CH4 | NH3 | H2O | HF |  |
| H2S | HCl | |||
| weak acids | HBr | |||
| strong acids | HI | |||
Strong acids react with water to the extent (extent of conversion of reactants to products - often expressed as a percentage) of 100%
| HA strong acid | + |  base |  |
 | + | A– |
H3O+ and A– are major species (A major species is present in relatively high concentration (>10% of the concentration of other species)) in an aqueous solution of a strong acid.
HA is a minor species (A minor species is present in very low concentration - less than 10% of the concentration of major species) in an aqueous solution of a strong acid.
HA is a minor species (A minor species is present in very low concentration - less than 10% of the concentration of major species) in an aqueous solution of a strong acid.
Weak acids react with water to the extent (extent of conversion of reactants to products - often expressed as a percentage) of less than 5%.
| HA strong acid | + | base |  |
| + | A– |
The equilibrium arrow () indicates that the reverse reaction is more important than the forward reaction.
HA is a major species and H3O+ and A– are minor species (A minor species is present in very low concentration - less than 10% of the concentration of major species) in an aqueous solution of a weak acid.
) indicates that the reverse reaction is more important than the forward reaction.HA is a major species and H3O+ and A– are minor species (A minor species is present in very low concentration - less than 10% of the concentration of major species) in an aqueous solution of a weak acid.