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A transition element forms at least one stable ion with an incomplete d subshell. Being in the d block alone is insufficient: zinc forms Zn2+ with a complete d subshell. Variable oxidation states reflect similar energies of outer s and d electrons. Transition metals and their compounds often act as catalysts; different oxidation states enable electron-transfer cycles, while surfaces can adsorb reactants and provide an alternative path. Explain a specific catalytic cycle or adsorption process rather than simply listing catalysis as a property.
Video by Eliot Rintoul. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Explain transition-metal properties
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: Why is zinc usually excluded from the transition-element definition?
Zn2+ has a complete d subshell. The definition requires an incomplete d subshell in at least one stable ion.
After watching 2: What does a ligand supply to a coordinate bond?
A lone pair of electrons. A ligand acts as an electron-pair donor.
What you'll be able to do
A transition element forms at least one stable ion with an incomplete d subshell. Being in the d block alone is insufficient: zinc forms Zn2+ with a complete d subshell. Variable oxidation states reflect similar energies of outer s and d electrons. Transition metals and their compounds often act as catalysts; different oxidation states enable electron-transfer cycles, while surfaces can adsorb reactants and provide an alternative path. Explain a specific catalytic cycle or adsorption process rather than simply listing catalysis as a property.
A complex contains a central metal ion bonded to ligands through coordinate bonds. Water and ammonia are common monodentate ligands; ethane-1,2-diamine is bidentate. Coordination number counts coordinate bonds to the centre, not necessarily the number of ligand molecules. Six coordinate bonds commonly give an octahedral shape, four can be tetrahedral or square planar, and two can be linear. Complexes may show cis–trans or optical isomerism depending on shape and ligand arrangement.
Ligands split the d-orbital energies. Absorption of selected visible wavelengths promotes electrons between these levels, and the transmitted complementary light gives the observed colour. Changing ligand, metal or oxidation state can change the splitting and colour. Adding concentrated chloride to aqueous copper(II) can favour a yellow chlorocomplex rather than the blue aqua complex. Ligand exchange need not change oxidation state. Chelating ligands can make particularly stable complexes because the substitution may be favoured by entropy.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: Does replacing water ligands around Cu2+ by chloride necessarily oxidise copper?
No: ligand substitution is distinct from redox.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.