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Homework Help: Dative bond confusion (or coordinate bond)

  1. Jan 28, 2007 #1
    I am a little confused with this. I know what a dative bond is, but the problem is when it comes to complex ions I do not understand.

    ok now for example

    [tex]NH_3[/tex] + [tex]H^+[/tex] = [tex]NH_4^+[/tex]

    So in this the lone pair of NH3 will fill the s- subshell of H and make it stable,

    but say in [tex]Cu^2^+[/tex]
    when this attracts six water molecules with six lone pairs, where do these lone pairs go? I mean what subshell does it fill?

    I really appreciate if you can help me with this.
    Thanks alot
    Last edited: Jan 28, 2007
  2. jcsd
  3. Feb 15, 2007 #2


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    they are dumped into the LUMO.
  4. Feb 19, 2007 #3
    They go into a higher energy orbital.

    Its more advanced than it seems though, The different shells actually sorta combine in a way called hybridisation, these shells form a difinitive shape. The lone pairs partially go into these hybridisation shells.

    i think someone else could probably describe it more correctly. i'm not too confidant on the subject myself.
  5. Feb 20, 2007 #4
    When cu2+ is hydrated, the lone pairs of electrons present on the oxygen atom of water are 'donated' to the d-orbital of the copper 2+ ion. This is why copper can form complexes (thats what the species is called).

    This species has a certain structure which depends on the type of ligand attacking (in this case water), the number of bonds formed, and where the lone pairs go. Here, the orbitals undergo dsp^3 hybridisation (that basically means the number of lone pairs present in the respective orbital: in this case, 1 in 3d, 1 in 4s, and 3 in 4p) to give the species trigonal bipyramidal geometry (a triangle with two bonds perpendicular to the plane sticking out of the center).

    Look up werner's theory/ability of d-block metals to form complexes if you want more detail.

    Another example of a complex is Tollen's reagent [Ag(NH3)4]+ which gives your famous silver mirror test for aldehydes.
  6. Feb 20, 2007 #5


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    If the copper is hydrated with 6 molecules of water, it cannot adopt a trigonal bipyramid structure. Only 5 ligands are required for a trigonalbipyramid...
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