13. The periodic table - the transition metals

13. The periodic table - the transition metals

13.1 First-row d-block elements

Nature of science:

• Looking for trends and discrepancies - transition elements follow certain patterns of behaviour. The elements Zn, Cr and Cu do not follow these patterns and are therefore considered anomalous in the first-row d-block.

Understandings:

• Transition elements have variable oxidation states, form complex ions with ligands, have coloured compounds, and display catalytic and magnetic properties.

• Zn is not considered to be a transition element as it does not form ions with incomplete d-orbitals.

• Transition elements show an oxidation state of +2 when the s-electrons are removed.

Applications and skills:

• Explanation of the ability of transition metals to form variable oxidation states from successive ionization energies.

• Explanation of the nature of the coordinate bond within a complex ion.

• Deduction of the total charge given the formula of the ion and ligands present.

• Explanation of the magnetic properties in transition metals in terms of unpaired electrons.

13.2 Coloured complexes

Nature of science:

• Models and theories - the colour of transition metal complexes can be explained through the use of models and theories based on how electrons are distributed in d-orbitals.

• Transdisciplinary - colour linked to symmetry can be explored in the sciences, architecture, and the arts.

Understandings:

• The d sub-level splits into two sets of orbitals of different energy in a complex ion.

• Complexes of d-block elements are coloured, as light is absorbed when an electron is excited between the d-orbitals.

• The colour absorbed is complementary to the colour observed.

Applications and skills:

• Explanation of the effect of the identity of the metal ion, the oxidation number of the metal and the identity of the ligand on the colour of transition metal ion complexes.

• Explanation of the effect of different ligands on the splitting of the d-orbitals in transition metal complexes and colour observed using the spectrochemical series.