AP | A-Level | IB | NCERT 11 + 12 – FREE NOTES, RESOURCES AND VIDEOS!
OCR (A) A-Level
YouTube Channel
YouTube Channel
@chemistry.student
*Revision Materials and Past Papers* 2.1.1 Atomic structure and isotopes 2.1.2 Compounds, formulae and equations 2.1.3 Amount of substance 2.1.4 Acids 2.1.5 Redox 2.2.1 Electron structure 2.2.2 Bonding and structure 3.1.1 Periodicity 3.1.2 Group 2 3.1.3 The halogens 3.1.4 Qualitative analysis 3.2.1 Enthalpy 3.2.2 Reaction Rates 3.2.3 Chemical equilibrium 4.1 Basic concepts and hydrocarbons 4.1.2 Alkanes 4.1.3 Alkenes 4.2.1 Alcohols 4.2.2 Haloalkanes 4.2.3 Organic synthesis 4.2.4 Analytical techniques 5.1.1 How fast? 5.1.2 How far? 5.1.3 Acids, bases and buffers 5.2.1 Lattice enthalpy 5.2.2 Enthalpy and entropy 5.2.3 Redox and electrode potentials 5.3.1 Transition elements 5.3.2 Qualitative analysis 6.1.1 Aromatic compounds 6.1.2 Carbonyl compounds 6.1.3 Carboxylic acids and esters 6.2.1 Amines 6.2.2 Amino acids, amides and chirality 6.2.3 Polyesters and polyamides 6.2.4 Carbon–carbon bond formation 6.2.5 Organic synthesis 6.3.1 Chromatography and qualitative analysis 6.3.2 Spectroscopy Required Practicals

5.3.1 Transition elements

Ligand substitutionLigands and complex ionsPrecipitation reactionsPropertiesRedox reactions

Properties

Specification Reference Topic 5.3.1 (a to c)

Quick Notes

  • Transition metals are d-block elements that form stable ions with incomplete d orbitals.
    • Their electronic configurations follow the pattern where 4s fills before 3d, but 4s is lost first when ions form.
    • They show variable oxidation states due to similar energies of orbitals in their 4s and 3d sub-shells.
  • Transition metal complexes are often coloured due to electron transitions between split d-orbitals.
  • Transition metals and their compounds are often used as catalysts.

Full Notes

Electronic Configurations of d-Block Elements

The 4s orbital fills before the 3d orbital when building up atoms, but 4s electrons are lost first when ions form.

Example Fe and Fe2+

Fe: 1s2 2s2 2p6 3s2 3p6 4s2 3d6

Fe2+: 1s2 2s2 2p6 3s2 3p6 3d6

Definition of a Transition Metal

Transition metals are d-block elements that form stable ions with partially-filled d-orbitals.

OCR A-Level Chemistry periodic table highlight showing d-block transition metals.

Scandium and zinc do not meet this definition in all oxidation states:

Hence, they are not considered transition metals in their common ions.

Variable Oxidation States

The small energy gap between 4s and 3d orbitals means different numbers of electrons can be readily lost, leading to multiple oxidation states.

E.g., manganese (Mn) can form a range of oxidation states from +2 to +7.

This makes transition metals useful in redox reactions and catalysis.

Transition metals are often used as catalysts because of their ability to form ions with different oxidation states and because of their (relatively) low reactivity.

Colour in Transition Metal Complexes

When species (called ligands) bond to a transition metal ion, the ion’s d-orbitals split into two energy levels (higher and lower).

This occurs because electrons in the d-orbitals are repelled by electrons from incoming ligands.

OCR A-Level Chemistry diagram showing crystal field splitting of d-orbitals into higher and lower energy levels.

Electrons can absorb energy from visible light to move from a lower energy level (ground state) to a higher one (excited state).

OCR A-Level Chemistry illustration of d–d transition where visible light promotes an electron between split d-orbital levels.

The remaining wavelengths of light are transmitted or reflected, giving the solution its observed colour.

Colour changes occur when:

No colour is seen if the metal has a full (d10) or empty (d0) d sub-shell, so no electron transitions can occur.

Summary