(a)    Proton containing solvents (protonic or protic)
(b)    proton free solvents (non-protonic or aprotic)
(c)    Amphoteric solvents

These solvents contain ionizable protons. They are generally acidic; Examples are HF, H₂SO₄ etc. These solvents have a strong tendency to donate protons. Even ammonia which is a base is a protic solvent and can ionize to give H⁺ ions to stronger bases. These solvents have strong tendency to accept protons. These solvents undergo auto-ionization. Some examples are:

       3HF  <==>  H₂F⁺ + HF₂^-
2H₂SO₄  <==>  H₃SO₄⁺ + HSO₄^-
    2NH₃  <==> NH₄⁺ + NH₂^-

These solvents can be categorized into two types :

Acetonitrile (CH₃CN), N, N-dimethylformamide [HCON (CH₃)₂]. dimethylsuphoxide (DMSO), sulphur dioxide (SO₂) are some common examples of this type. These compounds are aprotic and so not show evidence of undergoing self-ionization. These solvents are known to strongly solvate ions.

Chloring trifluoride (CIF₃), bromine trifluoride (BrF₃) and phosphorus oxychloride (POCI₃) are some common examples of this type. These solvents do not contain proton but undergo self-ionization.

   2CIF₃  <==>  CIF₂⁺ + CIF₄^-
    2BrF₃  <==>  BrF₂⁺ + BrF₄^-
2POCI₃  <==>  POCI₂⁺ + POCI₄^-

These solvents have hydrogen in their formula and can accept or donate protons depending onto eh nature of the reacting species. These solvents can act both as acids and bases and thus re called amphoteric solvents. These solvents dissociate very weekly into protons and anions. Examples are acetic acid and water. For example, acetic acid ionizes as an acid in water.

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