A-level [Transition metal-Complexes]

• hoay

  29 Dec 14, 04:07

  A sample of CuSO4 is stirred in excess of water a pale-blue solution is formed the specie responsible is [Cu(H2O)6]2+ ion. A sample of NiSO4 gave green colour complex having formula [Ni(H2O)6]2+. Why 6 water always shown?? can't they be 7 or 5?

• UltimaOnline

  29 Dec 14, 06:01

  Originally posted by hoay:

  A sample of CuSO4 is stirred in excess of water a pale-blue solution is formed the specie responsible is [Cu(H2O)6]2+ ion. A sample of NiSO4 gave green colour complex having formula [Ni(H2O)6]2+. Why 6 water always shown?? can't they be 7 or 5?

  
  The topic of complex ions is more complex than can be properly understood at A levels. The simple A level version is : water ligands are small, and hence 6 water ligands are able to surround any hydrated metal cation. 6 is the ideal number of ligands, because the more bonds formed, the more exothermic and thermodynamically favourable, but too many ligands (eg. 7 or 8) can cause steric overcrowding and van der Waals strain. So 6 is the ideal number.