Hydrated Ions as Examples of a Coordination Complex

The Chemistry of Art > 5. Complexes > Hydrated Ions as Examples of a Coordination Complex >

Describe hydrated ions as examples of a coordination complex or a complex ion and identify examples

  • For many metal cations, (particularly transition metals) the water molecules bond to them
    • Via co-ordinate covalent bonds from the oxygen atom
  • Vacant orbitals in the transition metals can be filled be any molecules or anions that have a lone pair of electrons to donate


  • A complex ion has
    • A central metal cation
    • Surrounded by a group of anions or molecules
    • These are known as ligands
  • Compounds that contain complex ions are called coordination compounds


  • Examples include
    • Anions (E.g Cl or CN)
    • Polar molecules (E.g H2O or NH3)
  • Co-ordinate covalent bonds form between the ligands and the transition metal ion
    • Uses the lone pair electrons of the ligand

Hydrated coordinate examples:

  • Cobalt (II) Chloride hexahydrate (CoCl2.6H2O)
  • Magnesium sulphate heptahydrate (MgSO4.7H2O)
  • Sodium tetraborate decahydrate (Na2B4O7.10H2O_
  • Calcium sulphate dihydrate (CaSO4.2H2O)

How to draw the above

  • Co-ordiantes of cation will be told to you
  • Draw a Lewis dot structure of the ligands to figure out how many dentates it has (Due to electronegativeity etc)
  • Draw the negative polar end towards the centre and connect with an arrow to indicate a co-ordinate bond has taken place