Structure 3.1 The periodic table: Classification of elements (HL)
Structure 3.1.7
Understandings:
  • Discontinuities occur in the trend of increasing first ionisation energy across a period.
Learning outcomes:
  • Explain how these discontinuities provide evidence for the existence of energy sublevels.
Additional notes:
  • Explanations should be based on the energy of the electron removed, rather than on the “special stability” of filled and half-filled sublevels.
This video covers the discontinuities of first ionisation energy across a period. 
Structure 3.1.8
Understandings:
  • Transition elements have incomplete d-sublevels that give them characteristic properties.
Learning outcomes:
  • Recognize properties, including: variable oxidation state, high melting points, magnetic properties, catalytic properties, formation of coloured compounds and formation of complex ions with ligands.
Additional notes:
  • Knowledge of different types of magnetism will not be assessed.
Linking questions:
  • Structure 2.3 What are the arguments for and against including scandium as a transition element?
This video covers the transition elements.
This video covers the magnetic properties of the transition elements. 
This video covers the structure and bonding of complex ions. ​
This video covers ligands. ​
This video covers how to deduce the charge and oxidation state of a central metal ion. ​
Structure 3.1.9
Understandings:
  • The formation of variable oxidation states in transition elements can be explained by the fact that their successive ionisation energies are close in value. 
Learning outcomes:
  • Deduce the electron configurations of ions of the first-row transition elements.
This video covers the variable oxidation states of the transition elements. 
Structure 3.1.10
Understandings:
  • Transition element complexes are coloured due to the absorption of light when an electron is promoted between the orbitals in the split d-sublevels. The colour absorbed is complementary to the colour observed.
Learning outcomes:
  • Apply the colour wheel to deduce the wavelengths and frequencies of light absorbed and/or observed.
  • The colour wheel and the equation c = λf are given in the data booklet.
Additional notes:
  • Students are not expected to know the different splitting patterns and their relation to the coordination number.
Linking questions:
  • Reactivity 3.4 What is the nature of the reaction between transition element ions and ligands in forming complex ions?
This video covers colour of complex ions. ​