Transition Metals

Question 1

D-block transition metals

Answer 1

Metals with an incomplete d-subshell in at least one of their ions.

Question 2

What are the exceptions to the Aufbau principle?

Answer 2

Copper (Cu) and Chromium (Cr)

Question 3

Why are Cu and Cr exceptions?

Answer 3

Due to the special stability associated with the d subshell being half or completely filled.

Question 4

Oxidation number rules

Answer 4

• 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 the molecule or neutral ion 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 5

How can a transition metal have different colours?

Answer 5

Compounds of the same transition metal in different oxidation states may have different colours.

Question 6

Oxidation

Answer 6

Increase in oxidation number.

Question 7

Reduction

Answer 7

Decrease in oxidation number.

Question 8

Oxidising agents

Answer 8

Tend to be compounds with metals in high oxidation states.

Question 9

Reducing agents

Answer 9

Tend to be compounds with metals in low oxidation states.

Question 10

Ligands

Answer 10

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 11

Coordination number

Answer 11

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

Question 12

When are d orbitals no longer degenerate

Answer 12

In a complex of a transition metal.

Question 13

Splitting of d orbitals

Answer 13

Occurs when the electrons present in approaching ligands cause the electrons in the orbitals lying along the axes to be repelled.

Question 14

Strong field ligands

Answer 14

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

Question 15

Weak field ligands

Answer 15

Cause a small energy difference between subsets of d orbitals

Question 16

Spectrochemical series

Answer 16

Ligands placed in order of their ability to split d orbitals.

Question 17

How do colours arise in transition metals?

Answer 17

Can be explained in terms of d-d transitions. Light is absorbed when electrons in a lower energy d orbital are promoted to a d orbital of higher energy. If light of one colour is absorbed, then the complementary colour will be observed.

Question 18

When do electrons transition to higher energy levels?

Answer 18

When energy corresponding to the ultraviolet or visible regions of the electromagnetic spectrum is absorbed.

Question 19

Heterogenous catalyst

Answer 19

They are in a different state to the reactants. Can be explained 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 20

Homogenous catalysts

Answer 20

In the same state as the reactants. Can be explained in terms of changing oxidation states with the formation of intermediate complexes.