MediumChemistryHigh School (11–12)Coordination Compounds › Bonding: Valence Bond and Crystal Field TheoryConceptualNumericalA-LevelIBNEET
Four aqua complexes are [Sc(H₂O)₆]³⁺, [Zn(H₂O)₆]²⁺, [Cr(H₂O)₆]³⁺ and [Co(H₂O)₆]²⁺…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Four aqua complexes are , , and . The atomic numbers of scandium, zinc, chromium and cobalt are 21, 30, 24 and 27. Count the d electrons of each metal ion, and say how many of the four complexes are coloured.
Need a reminder? The key ideaShow
A d-d transition absorbs light of wavelength , and for a or ion in kJ/mol with in nm. The colour seen is opposite the colour absorbed. A or ion has no d-d transition. At , in kJ/mol, where is the stability constant.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The d counts. has d electrons. has . has . has .
Step 2. Which can absorb? The ion has no electron to move. The ion has no empty d orbital to move to. Both complexes are colourless. The and ions have both an electron and a place for it, so they make a d-d transition.
Answer: 2 complexes are coloured, those of chromium (violet) and cobalt (pink). The scandium and zinc complexes are colourless.
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