Transition Metals

Question 1

Transition metals

Answer 1

(d-block elements which can) form stable ions with incompletely filled d-orbitals.

Question 2

Why can transition metals show variable oxidation numbers

Answer 2

it doesn’t require much energy for them to lose electrons as the 4s and 3d subshells are very
close in energy (they lose electrons from the 4s first)

Question 3

Ligand

Answer 3

Ion or molecules that donates electron pairs to metal

Question 4

Dative bonding

Answer 4

Bond formed when one atom provides both electrons. (Happens with a ligand binding to a metal ion)

Question 5

Complex ion

Answer 5

Metal ion surrounded by one or more ligands

Question 6

Why do transition metals form coloured ions in solution

Answer 6

• when ligands bind the d-orbitals split in energy
• when light of a certain wavelength can excite the electrons from a lower to higher energy d-orbital (d-d transition)
• we see the wavelengths transmitted (not absorbed)

Question 7

Why might there be a colourless solution formed for a transition metals show complex

Answer 7

• the ligands still cause the d-orbitals to split in energy level
• however no d-d transitions occur because either:
  *there are no electrons in the subshell to promote
  *the d-subshell is full and so there is no space to promote an electron

Question 8

Coordination number

Answer 8

Number of ligand ions which can attach to a metal

Question 9

Difference between monodentate and bidentate ligands

Answer 9

monodentate - only have one ‘tooth’
- can only bind once (form on dative covalent bond) to a metal ion eg Cl-bidentate - two ‘teeth’ - can bind twice to a metal ion eg
H2NCH2CH2NH2

Question 10

Tetrahedral complex

Answer 10

Formed by transition metals with large ligands eg anything with 4Cl- as ligands

Question 11

Square planar complexes

Answer 11

Complexes with four ligands in a square arrangement, mainly with Pt complexes

Question 12

Reasons why transition metals may change colour during reactions

Answer 12

Redox reaction - so changing oxidation state, meaning different number of electrons in the d-orbitals so different d-d transitions
Ligand exchange - different ligands and different shapes cause the d-orbitals to split differently so the energy gap is different, resulting in different colours from d-d transitions

Question 13

Haemoglobin

Answer 13

Fe(II) complex containing a multidentate ligand

Question 14

Amphoteric behaviour

Answer 14

Ability of a substance to act as an acid or a base

Question 15

Homogeneous and heterogeneous catalysts meaning

Answer 15

Homogeneous - same phase
Heterogeneous - different phase

Question 16

How does a heterogeneous catalyst work

Answer 16

-Adsorption of reactants onto surface of catalyst
-Weakening and breaking of bonds, to allow new ones to form
-Desorption of product from surface of catalyst

Question 17

How a homogeneous catalyst works

Answer 17

In the same phase as the reactants
Goes via an intermediate species

Question 18

Example of an auto catalyst

Answer 18

2MnO4-(aq) + 5C2O42-(aq) + 16H+(aq) →
2Mn2+(aq) + 10CO2(g) + 8H2O(I)
Mn2+ is generated in the reaction, it then catalyses the reaction.
Reaction starts off slowly as anions repel
Then speeds up as Mn2+ is formed
Slows down towards the end of the reaction as the concentration of the reactants are very
low.
Observe: purple -> colourless + fizzing