# What is that process called in which we add water molecules to an ion to form a complex?

An example would be $\ce{[Fe(H2O)6]^2+}$ in which it has 6 water molecules associated with it. What is the process of adding these water molecules called?

• What makes you think there exist some specific term for this particular kind of complexation? – Wildcat Jun 21 '15 at 12:39
• Are you referring to "hydration"? – ron Jun 21 '15 at 13:16
• @ron thank you but i am confused is this called hydration ?Then what is that called $\ce{FeSO4.5 H2O}$? The water of crystallization is also said to be a result of hydration reaction.Please clarify!! – Satyajeet Jun 21 '15 at 13:40
• $\ce{[Fe(H2O)6]^{2+}}$ and $\ce{[FeSO4(H2O)5]}$ are both examples of hydrated iron. In the latter compound, one of the water ligands has been replaced by a sulphate ligand. – ron Jun 21 '15 at 13:49
• @ron what i am thinking is the first ion actually has coordinated $\ce{H2O}$ bonded to $\ce{Fe^2+}$ and in the second case the water of crystallisation is surrounding the compound FeSO4 by electrostatic attractions. – Satyajeet Jun 21 '15 at 13:55

I believe it is normally just called "addition of water". There is also the term "hydration" but this can also refer to the addition of water to alkenes or alkynes which forms alcohols (in the case of alkene; I am not sure about alkynes). For example, $$\ce{CH2=CH2 \text{(ethene/alkene)} + H2O -> CH3CH2OH \text{(ethanol/alcohol)}}$$