colours and complex ions

Question 1

What changes in a complex of a transition metal and how?

Answer 1

The subshells of the orbitals are no longer degenerate.

The ligands approach through the axis and split the d orbitals making them no longer degenerate.

Question 2

What causes the splitting of d orbitals to higher and lower energies to occur?

Answer 2

When ligands bond to the central metal ion, the electrons present in the approaching ligand cause the electrons in the d orbitals lying along the axis to be repelled in the metal ions

This repulsion causes the 5 d orbitals to split into two different sets: 2 with higher energy and 3 with lower energy

This energy difference between the two sets of d orbitals corresponds to the wavelengths of visible light

(causes colour)

Question 3

What are strong field ligands and weak field ligands?

Answer 3

Strong field-ligands that cause a large difference in energy between subsets of d orbitals

Weak field-ligands that cause a small energy difference

Question 4

What is the spectrochemical series?

Answer 4

The order of ligand’s abilities to split d orbitals

Question 5

How can colours of many transition metal complexes be explained?

Answer 5

in terms of d-d transitions

Question 6

When is light is absorbed?

Answer 6

When electrons in a lower energy d orbital are promoted to a d orbital of higher energy

Question 7

What is observed when light of one colour is absorbed

Answer 7

Complementary colour

Question 8

When do electrons transition to higher energy levels?

Answer 8

When energy corresponding to the UV or visible regions of the EM spectrum are absorbed

Question 9

What can act as catalysts?

Answer 9

transition metals and their compounds

Question 10

How can heterogeneous catalysis be explained?

Answer 10

in terms of the formation of activated complexes and the adsorption of reactive molecules onto active sites. The presence of unpaired d electrons or unfilled d orbitals is thought to allow activated complexes to form. This can provide reaction pathways with lower activation energies compared to the uncatalysed reaction

Question 11

How can homogeneous catalysis be explained

Answer 11

in terms of changing oxidation states with the formation on intermediate complexes

Question 12

Difference between heterogeneous and homogeneous catalysts.

Answer 12

heterogeneous-are in a different state to the reactants

homogeneous- are in the same state as the reactants

Question 13

Order of strengths of field of ligands

Answer 13

I- < Br- < Cl- < F- < H2O < NH3 < CN-

Question 14

How can transition metals absorb light?

Answer 14

(due to split d orbitals)

because photons (at a particular energy and therefore particular wavelength) excite electrons in the lower d-orbitals (ground state) up to a higher energy d-orbital (excited state)

This absorbed energy dissipates as heat energy and does not reemerge as light energy

Question 15

How do transition metal complexes get their colour?

Answer 15

If the energy absorbed in the d-d transition is in the visible region of the EM spectrum, the colour of the transition metal complex will be the complementary colour of the colour absorbed

Question 16

Why do transition metals make good catalysts!

Answer 16

They can form a variable number of bonds due to the availability of unoccupied and half-filled d- orbitals (this allows the easier formation of intermediate complexes->this provides reaction pathways of lower energy to proceed)

The variability of oxidation state is another important factor (the transition metal reverts to original oxidation state once the reaction is complete)