Transition Metals and Coordination Compounds
What you must know
Transition metals show variable oxidation states, form coloured ions, act as catalysts and form complex ions. Know ligand types (monodentate, bidentate, polydentate such as EDTA), coordination number, and the naming and formula conventions of complexes. Understand isomerism - geometric (cis/trans), optical, and ionisation/hydrate isomerism. Recognise why complexes are coloured (d–d transitions split by ligands) and how ligand strength affects splitting. Know common oxidation states of Fe, Cu, Mn, Cr and their characteristic colours.
Traps
- Writing the charge of a complex ion incorrectly; sum ligand charges and metal oxidation state carefully.
- Confusing coordination number with oxidation state.
- Forgetting that Zn²⁺ is d¹⁰ and therefore colourless.
- Naming ligands in the wrong alphabetical order or omitting the metal oxidation state in Roman numerals.
Worked example
Name [Cu(NH₃)₄]SO₄. The complex cation has four ammonia ligands and copper in oxidation state +2 (sulfate is −2). Name: tetraamminecopper(II) sulfate. Rule of thumb: list ligands alphabetically, then the metal with its oxidation state in parentheses, then the counter-ion.