Inorganic Chemistry
Inorganic Chemistry
The inorganic section of NEB Class 12 focuses on transition metals, coordination compounds, heavy metals and periodic trends. Questions ask you to write configurations, assign oxidation states, name complexes and explain colour or magnetism using crystal-field ideas.
Core rules
- A transition metal has an incomplete d subshell in atom or common ion. Cr is [Ar]3d5 4s1 and Cu is [Ar]3d10 4s1 because half-filled and fully filled d orbitals are extra stable.
- Variable oxidation states arise from small 3d–4s energy gaps; Mn shows +2 to +7.
- Complex naming: ligands alphabetically, then metal with oxidation state in Roman numerals. Anionic complexes end in -ate, e.g. [Fe(CN)6]4− is hexacyanoferrate(II).
- Colour comes from d–d transitions; magnetic moment μ = √(n(n+2)) BM, where n = unpaired electrons.
- Heavy-metal chemistry (Pb, Hg, Cd, As) stresses toxicity, detection and treatment; PbSO4 insolubility is used in qualitative tests.
Worked example
Find the magnetic moment of Fe3+.
Reasoning: Fe is [Ar]3d6 4s2; Fe3+ loses three electrons, giving [Ar]3d5. That is five unpaired electrons. μ = √(5×7) = √35 = 5.92 BM. Because the moment is close to the spin-only value, the complex is high-spin unless a strong-field ligand forces pairing.
Traps
Counting total d electrons instead of unpaired ones; forgetting the charge in complex names; placing ligands in the wrong alphabetical order; calling Zn a typical transition metal although Zn2+ is d10; and confusing low-spin with low oxidation state.