Playbook
Coordination Compounds
88 q - 2.12/paper - 2% HARD. Counting — donor atoms, oxidation state, EAN, unpaired electrons.
- Questions in the bank
- 88
- q/paper (2024–25 papers)
- 2.12
- Tagged HARD
- 2%
- Subtopics
- 5
Strand: Recall
When you’ll see it
A complex ion — its ligands, oxidation state, coordination number, name, isomers, hybridisation or magnetism.
How this chapter is tested
88 q at 2.12 a paper, 2% HARD, and most of it is counting rather than memory. Ligands and denticity (33 q) is the largest page: en is bidentate, EDTA hexadentate, and ambidentate ligands (NO₂⁻, SCN⁻) bind through either atom.
Oxidation state is the metal's charge after subtracting the ligands'. EAN = atomic number − oxidation state + 2 × coordination number. Magnetism counts unpaired electrons after the ligand has (or has not) forced pairing.
The sub-skills
The distinct skills inside the chapter, in the order to learn them.
Denticity
Mono: NH₃, Cl⁻, H₂O. Bi: en, ox²⁻. Hexa: EDTA⁴⁻.
Oxidation state and CN
Charge of the complex minus the ligands' charges; CN = number of donor atoms.
EAN
Z − oxidation state + 2 × CN; 36 for many stable complexes (the krypton number).
Magnetism
Strong-field ligands (CN⁻, CO) pair electrons; weak-field (F⁻, H₂O) leave them unpaired.
Traps to expect
Distractor shapes this chapter reuses. The Traps page covers the patterns that cut across chapters.
Counting ligands instead of donor atoms
[Co(en)₃]³⁺ has three ligands but coordination number 6 — each en binds twice.
The ligand's charge
Oxidation state of Fe in [Fe(CN)₆]⁴⁻ is +2: −4 = x + 6(−1).
Learn it before you drill it
This chapter has full teaching notes — foundations, worked examples, self-checks and a per-subtopic mastery checkpoint. Read the notes once, then drill subtopic by subtopic below.
Coordination Compounds notesDrill every coordination compounds question
88 questions from the bank, scoped to 5 bundled subtopics.
Drill one subtopic at a time
The 5 subtopics this playbook covers, in catalog order.
Related playbooks
Often paired with this one — the technique, the trap or the taxonomy overlaps. Drill these next.