The middle block of the periodic table, the 'd' block, so called due to the partially filled 'd' shells of electrons, is a large and important group of elements, many of which have practical uses in society.
Essential idea: The transition elements have characteristic properties; these properties are related to their all having incomplete 'd' sub-levels.
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.
Essential idea: d-orbitals have the same energy in an isolated atom, but split into two sub-levels in a complex ion. The electric field of ligands may cause the d-orbitals in complex ions to split so that the energy of an electron transition between them corresponds to a photon of visible light.
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 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.
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.
In Chapter 5.4