13.2 Coloured complexes (HL) Flashcards
What happens when light passes through a solution with transition metal ions?
Wavelengths are absorbed and emitted
If a compound emits blue, what wavelengths are absorbed?
Orange and possibly red
How does the colour wheel help?
It allows us to look at complementary colors and hence know which wavelength is absorbed when another is emitted
Why are some compounds like those with Cu+ and Sc3+ colourless?
Because the d sublevel is empty and hence doesn’t form colored compounds
What does it mean by “All 5 d orbitals are degenerate”?
It means they have the same energy
What happens to d sublevel when ligand bonds to central metal ion?
It experiences repulsion and they become non-degenerate. This splits them into 2 higher energy orbitals and 3 lower energy
What is a d-d transition?
All transition metals have atleast one half-filled d orbital so electrons can transition from lower to higher set of orbital by absorbing energy
Why are transition metals coloured?
Because some colour is absorbed when electrons are excited in split d orbitals. Not due to the transitions between levels
Relation between spectrochemical series and splitting of orbitals
Ligands higher up in the series produce larger splitting of orbitals like CO and CN- as compared to ligands which are lower like halides
What type of wavelength do stronger ligands absorb?
Shortwave as they are of higher energy
What can affect the strength of repulsion beside nature of ligands?
- Identity of metal ions (Different configurations = diff. repulsion and energy increases as one descends a group)
- Geometry of complex ion
- Oxidation state of metal
Relation between energy absorbed and oxidation state and why
Energy absorbed increases as oxidation state increases.
- Charge on metal ion increases so more charge density and more distance between ligand and metal ion decreases causing overlap between orbitals which equals greater repulsion and hence increase in wavelength absorbed
Which causes greater splitting amongst the two isoelectronic complexes: [Fe(H2O)6]3+ and [Mn(H2O)6]2+
[Fe(H2O)6]3+. Since they have the same no. of electrons, identity of metal will matter. As nuclear charge of Fe is 26+ while for Mn it’s 25+, ligands are pulled closer to Fe3+ and hence cause greater splitting.
