GROUP 15 (N, P, As, Sb, Bi):
  Electronic config: ns²np³ (half-filled, stable)
  N₂: very stable (triple bond) | N₂O, NO, NO₂, N₂O₃, N₂O₄, N₂O₅ (oxides)
  NH₃: trigonal pyramidal, sp³, strong reducing agent, forms ammonium salts
  HNO₂ (nitrous acid) | HNO₃ (nitric acid): strong oxidizing acid
  Phosphorus allotropes: white (reactive), red, black, violet
  PH₃: trigonal pyramidal, weaker base than NH₃, less H-bonding
  Phosphine vs ammonia: P is larger, PH₃ bond angle (93.5°) smaller than NH₃ (107°)

GROUP 16 (O, S, Se, Te, Po):
  O₂: paramagnetic (2 unpaired electrons), diatomic
  Allotropes of O: O₂ and O₃ (ozone)
  Ozone: sp² hybridised, V-shaped, O-O bond order 1.5, strong oxidizing agent
  H₂O: V-shaped 104.5°, extensive H-bonding (high boiling point)
  H₂O₂: pale blue liquid, oxidizing AND reducing agent, non-planar structure
  SO₂: bent molecule, sp³ (with one lone pair), acidic, bleaching agent
  SO₃: trigonal planar, sp², reacts with water → H₂SO₄
  Sulphuric acid (H₂SO₄): strong acid, dehydrating, oxidizing, oily liquid

GROUP 17 (F, Cl, Br, I):
  Halogens: oxidizing agents, high EA
  HF: strongest H-bonding | HCl: most stable thermally | HI: strongest reducing
  Cl₂: pale yellow-green, bleaching due to nascent oxygen from Cl₂+H₂O→HCl+HOCl
  Interhalogen compounds: ClF, ClF₃, BrF₃, BrF₅, IF₇ (higher halogen central)
  
GROUP 18 (Noble Gases):
  Electronic config: completely filled (stable)
  All gases at room temperature | very low reactivity
  Xe compounds: XeF₂ (linear), XeF₄ (square planar), XeF₆ (distorted octahedral)

ALCOHOLS:
  Primary → aldehyde (partial oxidation) → carboxylic acid (complete)
  Oxidizing agents: K₂Cr₂O₇/H₂SO₄, KMnO₄, PCC (for primary→aldehyde only)
  Dehydration (>170°C with H₂SO₄): alcohol → alkene
  Lucas test: ZnCl₂/conc HCl | 3° immediate cloudiness | 2° slow | 1° no reaction

ALDEHYDES and KETONES:
  Fehling's test: only aldehydes (blue → brick red precipitate)
  Tollens' test: only aldehydes (silver mirror)
  Aldehyde: CrO₃ in dry ether or PCC
  Both: react with NaBH₄ and LiAlH₄ (reduction to alcohol)
  Iodoform test: CH₃COR or CH₃CHOH-R (methyl ketones / secondary alcohol with methyl)

CARBOXYLIC ACIDS:
  Acidic due to -I effect of C=O and resonance stabilisation of carboxylate ion
  Acidity: HCOOH > CH₃COOH > C₂H₅COOH (more alkyl = more +I effect, less acidic)
  Haloacids: Cl₃CCOOH > Cl₂CHCOOH > ClCH₂COOH > CH₃COOH (more Cl = more acidic)

AMINES:
  Basicity: 3° > 2° > 1° > NH₃ (in gas phase, inductive effect dominates)
  But in water: 2° > 1° > 3° > NH₃ (solvation effect changes order)
  Diazonium salts: ArNH₂ + NaNO₂ + HCl at 0°C → ArN₂⁺Cl⁻
    Coupling reaction: → azo dye (yellow-orange-red)
    Sandmeyer: ArN₂⁺ + CuX → ArX (X = Cl, Br, CN)