DM - Metal complexes and colour Flashcards
What do ligands split?
The 3d subshell into 2 energy levels.
What happens to the energy of the orbitals when ligands bond to the ions/what changes?
Usually the 3d orbitals of transition metal ions all have the same energy.
When ligands bond to the ions, some of the orbitals gain energy, splitting the 3d orbitals into two different energy levels.
Which energy state do electrons usually occupy?
The lower orbitals - the ground state.
What do electrons need to jump up to higher orbitals (excited states)?
Energy equal to the energy gap, ΔE.
How do electrons get the energy to allow them to jump from ground state to the excited state?
From visible light.
The amount of energy needed to make electrons jumps depends on what?
The central metal ion and its oxidation state, the ligands and the coordination number.
Why does the amount of energy needed to make electrons jumps depend on the central metal ion and its oxidation state, the ligands and the coordination number?
As these affect the size of the energy gap (ΔE).
What are the colours of compounds complementary to?
Those colours that are absorbed.
What happens when visible light hits a transition metal ion?
Some frequencies are absorbed when electrons jump up to the higher orbitals.
The frequencies of light absorbed by a transition metal ion depends on what?
The size of the energy gap (ΔE).
What is the relationship between the size of the energy gap (ΔE) and the frequency of light absorbed?
The larger the energy gap, the higher the frequency of light that is absorbed.
What happens to the rest of the frequencies that aren’t absorbed by the transition metal ion?
They are transmitted or reflected.
What do the frequencies that are transmitted or reflected do?
Combine to make the complement of the colour of the absorbed frequencies - this is the colour that you see.
What happens if there are no 3d electrons or the 3d sub-level is full?
Then no electrons will jump, so no energy will be absorbed.
What will it look like if there’s no energy absorbed?
The compound will look white or colourless.
What are the precipitates like for transition metal hydroxides?
Brightly coloured.
What do you get when you mix an aqueous solution of transition metal ions with aqueous sodium hydroxide (NaOH) or aqueous ammonia (NH3)?
A coloured hydroxide precipitate.
What form will transition metals take in aqueous solutions?
[Mn(H2O)6]^n+.
They can also be written as M^n+ (aq), as long as the metal ion is only bonded to water.
What is the colour change when copper(II) goes from solution to hydroxide precipitate?
Pale blue solution to blue precipitate.
What is the colour change when iron(II) goes from solution to hydroxide precipitate?
Pale green solution to a green precipitate which darkens on standing.
What is the colour change when iron(III) goes from solution to hydroxide precipitate?
Yellow solution to an orange precipitate which darkens on standing.
What happens for copper(II) hydroxide but not for iron(II) hydroxide and iron(III) hydroxide?
Goes on to form complexes with ammonia.
What can ligands do with each other?
Exchange places with one another.
What is ligand substitution?
When one ligand is swapped for another ligand.
What does ligand substitution usually cause?
A colour change.
What happens if the ligands swapped in ligand substitution are of similar size?
The coordination number of the complex ion doesn’t change and neither does the shape.
Give examples of ligands which are similar sizes
H2O
NH3
CN-
What happens if the ligands swapped in ligand substitution are of different sizes?
There is a change of coordination number and a change of shape.
Give examples of ligands which are different sizes
H2O and Cl-
Can ligand substitution be partial?
Yes
Do you need to include all the water ligands when writing the formula of a complex?
Yes if it is in solution and contains ligands that aren’t water but not if you are writing out the formula of a precipitate.
