Periodicity and Inorganic Chemistry covers trends across periods and down groups, the chemistry of Groups 2 and 7, transition metal properties (variable oxidation states, complex ions, colour), and electrochemistry.
Across a period: atomic radius decreases (more protons, same shielding), IE increases, electronegativity increases. Down a group: radius increases, IE decreases, electronegativity decreases. Period 3 oxides: Na₂O, MgO (ionic, basic) → Al₂O₃ (amphoteric) → SiO₂ (giant covalent) → P₄O₁₀, SO₃, Cl₂O₇ (covalent, acidic). Group 2: react with water → metal hydroxide + H₂. Reactivity increases down (easier to lose 2 electrons). Solubility of hydroxides increases down group; solubility of sulfates decreases. Group 7: reactivity decreases down (harder to gain electron). Halogen displacement. Chlorine + NaOH: Cl₂ + 2NaOH → NaCl + NaClO + H₂O (disproportionation). Test for halides: add AgNO₃ → AgCl (white), AgBr (cream), AgI (yellow).
Transition metals: d-block elements with incomplete d sub-shell (in at least one stable ion). Properties: variable oxidation states, form coloured ions, catalytic activity, complex ion formation. Complex ions: central metal ion + ligands (species with lone pair). Coordination number: number of coordinate bonds. Common shapes: octahedral (6 ligands), tetrahedral (4), square planar (4). Colour: d-d electron transitions (split d orbitals absorb specific wavelengths). Ligand substitution reactions. Redox: oxidation = loss of electrons; reduction = gain. Oxidation states. Half-equations balance: balance atoms, then balance charges with electrons. Electrode potentials E°: measured relative to standard hydrogen electrode. Cell emf = E°(cathode) − E°(anode). Reaction feasible if emf > 0. Redox titrations: MnO₄⁻ (purple → colourless) with Fe²⁺ or C₂O₄²⁻.
In an isolated transition metal ion, all five d orbitals are degenerate (same energy). When ligands bond to the metal (forming a complex), the d orbitals split into two energy levels — the splitting depends on the ligand and geometry. In octahedral complexes, three orbitals go lower (t₂g) and two go higher (eg). When visible light hits the complex, electrons absorb specific wavelengths to jump from the lower to higher d orbitals (d-d transition). The colour we see is the complementary colour of what\'s absorbed. For example, [Cu(H₂O)₆]²⁺ absorbs red/orange light and appears blue. This only works if the d sub-shell is partially filled — d⁰ (Sc³⁺) and d¹⁰ (Zn²⁺) ions are colourless because no d-d transition is possible. Changing the ligand changes the splitting and thus the colour.
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