DM - Metal complexes and colour

Question 1

What do ligands split?

Answer 1

The 3d subshell into 2 energy levels.

Question 2

What happens to the energy of the orbitals when ligands bond to the ions/what changes?

Answer 2

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.

Question 3

Which energy state do electrons usually occupy?

Answer 3

The lower orbitals - the ground state.

Question 4

What do electrons need to jump up to higher orbitals (excited states)?

Answer 4

Energy equal to the energy gap, ΔE.

Question 5

How do electrons get the energy to allow them to jump from ground state to the excited state?

Answer 5

From visible light.

Question 6

The amount of energy needed to make electrons jumps depends on what?

Answer 6

The central metal ion and its oxidation state, the ligands and the coordination number.

Question 7

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?

Answer 7

As these affect the size of the energy gap (ΔE).

Question 8

What are the colours of compounds complementary to?

Answer 8

Those colours that are absorbed.

Question 9

What happens when visible light hits a transition metal ion?

Answer 9

Some frequencies are absorbed when electrons jump up to the higher orbitals.

Question 10

The frequencies of light absorbed by a transition metal ion depends on what?

Answer 10

The size of the energy gap (ΔE).

Question 11

What is the relationship between the size of the energy gap (ΔE) and the frequency of light absorbed?

Answer 11

The larger the energy gap, the higher the frequency of light that is absorbed.

Question 12

What happens to the rest of the frequencies that aren’t absorbed by the transition metal ion?

Answer 12

They are transmitted or reflected.

Question 13

What do the frequencies that are transmitted or reflected do?

Answer 13

Combine to make the complement of the colour of the absorbed frequencies - this is the colour that you see.

Question 14

What happens if there are no 3d electrons or the 3d sub-level is full?

Answer 14

Then no electrons will jump, so no energy will be absorbed.

Question 15

What will it look like if there’s no energy absorbed?

Answer 15

The compound will look white or colourless.

Question 16

What are the precipitates like for transition metal hydroxides?

Answer 16

Brightly coloured.

Question 17

What do you get when you mix an aqueous solution of transition metal ions with aqueous sodium hydroxide (NaOH) or aqueous ammonia (NH3)?

Answer 17

A coloured hydroxide precipitate.

Question 18

What form will transition metals take in aqueous solutions?

Answer 18

[Mn(H2O)6]^n+.

They can also be written as M^n+ (aq), as long as the metal ion is only bonded to water.

Question 19

What is the colour change when copper(II) goes from solution to hydroxide precipitate?

Answer 19

Pale blue solution to blue precipitate.

Question 20

What is the colour change when iron(II) goes from solution to hydroxide precipitate?

Answer 20

Pale green solution to a green precipitate which darkens on standing.

Question 21

What is the colour change when iron(III) goes from solution to hydroxide precipitate?

Answer 21

Yellow solution to an orange precipitate which darkens on standing.

Question 22

What happens for copper(II) hydroxide but not for iron(II) hydroxide and iron(III) hydroxide?

Answer 22

Goes on to form complexes with ammonia.

Question 23

What can ligands do with each other?

Answer 23

Exchange places with one another.

Question 24

What is ligand substitution?

Answer 24

When one ligand is swapped for another ligand.

Question 25

What does ligand substitution usually cause?

Answer 25

A colour change.

Question 26

What happens if the ligands swapped in ligand substitution are of similar size?

Answer 26

The coordination number of the complex ion doesn’t change and neither does the shape.

Question 27

Give examples of ligands which are similar sizes

Answer 27

H2O
NH3
CN-

Question 28

What happens if the ligands swapped in ligand substitution are of different sizes?

Answer 28

There is a change of coordination number and a change of shape.

Question 29

Give examples of ligands which are different sizes

Answer 29

H2O and Cl-

Question 30

Can ligand substitution be partial?

Answer 30

Yes

Question 31

Do you need to include all the water ligands when writing the formula of a complex?

Answer 31

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.