Transition Metals

Question 1

What is a transition metal?

Answer 1

An element with an incomplete d sub-shell in one of it’s stable ions

Question 2

What two transition metals do not follow the aufbau principle?

Answer 2

Chromium and copper

Question 3

Why do chromium and copper not follow the aufbau principle?

Answer 3

There is a special stability associated with the d sub-shell being half-filled or completely filled

Question 4

When a transition metal (in the first row) forms an ion is it the 3d or 4s electrons that are lost first?

Answer 4

4s

Question 5

How can you find the oxidation number?

Answer 5

• uncombined elements have an oxidation number of 0
• ions containing single atoms have an oxidation number that is the same as the charge on the ion
• in most of its compounds, oxygen has an oxidation number of −2
• in most of its compounds, hydrogen has an oxidation number of
+1
• the sum of all the oxidation numbers of all the atoms in a neutral
compound must add up to zero
• the sum of all the oxidation numbers of all the atoms in a polyatomic ion must be equal to the charge on the ion

Question 6

Can a transition metal have different oxidation states in it’s compounds?

Answer 6

Yes

Question 7

What may be different about compounds of the same transition metal in different oxidation states?

Answer 7

The colour

Question 8

Define oxidation.

Answer 8

An increase in oxidation number

Question 9

Define reduction.

Answer 9

A decrease in oxidation number

Question 10

Compounds containing metals in what oxidation state are often oxidising agents?

Answer 10

High

Question 11

Compounds containing metals in what oxidation state are often reducing agents?

Answer 11

Low

Question 12

What is a ligand?

Answer 12

Ligands may be negative ions or molecules with non-bonding pairs of electrons that they donate to the central metal atom or ion, forming dative covalent bonds.

Question 13

What is the coordination number?

Answer 13

The total number of bonds from the ligands to the central transition metal

Question 14

Why does splitting of the d orbitals occur in transition metal complexes?

Answer 14

The electrons present in approaching ligands cause the electrons in the orbitals lying along the axes to be repelled

Question 15

What is a strong field ligand?

Answer 15

Ligands that cause a large difference in energy between subsets of d orbitals

Question 16

What is a weak field ligand?

Answer 16

Ligands that cause a small difference in energy between subsets of d orbitals

Question 17

What is the spectrochemical series?

Answer 17

When ligands are placed in order of their ability to split d orbitals

Question 18

How can the colours of many transition metal complexes be explained?

Answer 18

d-d transitions

Question 19

If light of one colour is absorbed, what colour is observed?

Answer 19

The complementary colour

Question 20

Can transition metals and their compounds act as catalysts?

Answer 20

Yes

Question 21

What are heterogeneous catalysts?

Answer 21

Catalysts in a different state from the reactants

Question 22

How can heterogeneous catalysis be explained?

Answer 22

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 23

What are homogeneous catalysts?

Answer 23

Catalysts in the same state as the reactants

Question 24

How can homogeneous catalysts be explained?

Answer 24

In terms of changing oxidation states with the formation of intermediate complexes