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Beyond the textbook: counting the isomers of any complex, filling the crystal field levels and calculating the stabilisation energy and the spin-only magnetic moment, and comparing the colour and stability of complexes. The problems that JEE, NEET and A-Level Chemistry ask most, with a full timed paper.

What's inside

1. Counting the isomers of a complex: A die has six faces, and an octahedral complex has six corners. Paint the faces of a die and you meet every difficulty of counting isomers: the same die looks different when you turn it, and a die and its mirror image are not always the same. This lesson gives a method that counts every isomer once, a test for a mirror plane, and a check by division.
2. Crystal field stabilisation energy and magnetic moment: Each electron that enters the d orbitals of a complex has two choices: climb to the upper level or share a seat with another electron. The crystal field stabilisation energy counts the climbing. The full energy bill also counts the sharing. This lesson writes out the bill for any number of d electrons, compares the two spin states, and ends with the magnetic moment worked both ways.
3. Ligand strength, colour and stability orders: Which complex is more stable, which one absorbs light of the longer wavelength, which one is more strongly split? Exam questions often ask for an order. Three short rules answer almost all of them: the splitting is about a ligand factor times a metal factor, the wavelength follows the splitting, and stability follows charge, size and the number of rings.