Transition and Inner Transition Elements
Transition and Inner Transition Elements tests electronic configurations, oxidation states, colour, magnetism, catalytic behaviour, alloys and the lanthanoid contraction.
Core rules
- Transition elements have partially filled d orbitals in the atom or common ions; Zn, Cd and Hg are not typical transition metals.
- Cr ([Ar]3d5 4s1) and Cu ([Ar]3d10 4s1) are exceptions to the expected configuration.
- Colour arises from d-d transitions; ions with d0 or d10 are colourless.
- Magnetic moment μ = sqrt(n(n+2)) BM, where n is the number of unpaired electrons.
- Lanthanoid contraction: poor shielding by 4f electrons causes a gradual decrease in atomic radius from La to Lu.
- Actinoids show wider oxidation-state ranges and greater radioactivity.
Worked example
Find the magnetic moment of Fe3+. Fe is [Ar]3d6 4s2; Fe3+ is [Ar]3d5, so n = 5. μ = sqrt(5 x 7) = sqrt(35) = 5.92 BM. Reasoning: count unpaired d electrons in the ion, not in the neutral atom; a d5 high-spin ion has five unpaired electrons.
Traps
Counting 4s electrons after ionisation, treating Zn2+ as coloured, and saying lanthanoid contraction is due to increasing nuclear charge alone. Do not write that all transition metals are paramagnetic: d10 ions are diamagnetic.