Inorganic Chemistry
Inorganic chemistry in JAM CY tests periodic trends, chemical bonding, coordination compounds, solid-state structures, main-group chemistry, and organometallic/bioinorganic essentials. Expect to predict structure, spin state, stability, and magnetic behaviour from a few robust models.
Core rules
- Periodic trends: atomic radius decreases across a period and increases down a group; ionisation energy generally rises across a period; electron affinity has exceptions at group 2 and group 15.
- VSEPR: count σ bonds and lone pairs to assign geometry; lone-pair–lone-pair repulsion > lone-pair–bond-pair > bond-pair–bond-pair.
- Crystal field theory: in an octahedral field, t2g is lowered by 0.4Δo and eg raised by 0.6Δo. Strong-field ligands (CN−, CO, NO2−) favour low spin; weak-field ligands (F−, Cl−, Br−, I−) favour high spin.
- Spin-only moment: μ = √[n(n+2)] BM, where n is the number of unpaired electrons.
- The 18-electron rule is a guide for organometallics, not a law; main-group and early-transition complexes often deviate.
Worked example
Predict the spin state and magnetic moment of [Fe(CN)6]^3−. Fe is +3, so d5. CN− is strong field, so low spin: t2g^5 eg^0, one unpaired electron. μ = √[1(1+2)] = √3 = 1.73 BM. By contrast, high-spin d5 would give five unpaired electrons and μ = √35 ≈ 5.92 BM.
Traps
Forgetting the ligand charge when assigning oxidation state; using high-spin CFSE for strong-field complexes; confusing Δo with Δt; ignoring Jahn–Teller distortion for d9 and high-spin d4; and treating the 18-electron rule as universal.