Nitrogen (N₂): Triple bond (N≡N), very stable. Used as inert atmosphere. N₂ is NOT reactive under normal conditions despite being most electronegative (after O, F) — due to high bond dissociation energy (941 kJ/mol).
Oxides of nitrogen: N₂O (dinitrogen oxide — laughing gas, neutral), NO (nitric oxide — neutral), N₂O₃ (acidic), NO₂ (acidic, brown, toxic), N₂O₄ (dimer of NO₂), N₂O₅ (most acidic).
Oxoacids of nitrogen: HNO₂ (nitrous acid, +3), HNO₃ (nitric acid, +5 — concentrated is yellow due to dissolved NO₂). HNO₃ is a strong oxidising acid. Aqua regia = 3 parts HCl + 1 part HNO₃ → dissolves gold and platinum.
Phosphorus allotropes: White P (P₄, most reactive, toxic, glows in dark — phosphorescence, stored in water), Red P (polymeric, less reactive, non-toxic), Black P (most stable, semiconductor).
Oxoacids of phosphorus: H₃PO₄ (orthophosphoric, tribasic), H₃PO₃ (phosphorous/phosphonic acid, dibasic — one P-H bond), H₃PO₂ (hypophosphorous, monobasic — two P-H bonds). Basicity determined by P-OH groups, NOT P-H bonds.
Ozone (O₃): Allotrope of O. Bent shape (117.5°). Strong oxidising agent. Decomposes to O₂ at room temp. Ozone hole — depletion by CFCs and NOₓ in stratosphere. Freons (CHClF₂) react with O₃.
Sulphur allotropes: Rhombic S (α-S, stable at room temp, S₈ crown shape), Monoclinic S (β-S, stable above 96°C). Both have S₈ molecules. Plastic S (amorphous, elastic).
Oxoacids of sulphur: H₂SO₃ (sulphurous, +4), H₂SO₄ (sulphuric, +6 — concentrated is dehydrating agent, not oxidising unless hot concentrated), H₂S₂O₇ (oleum/pyrosulphuric acid), H₂S₂O₃ (thiosulphuric, used in photography — hypo).
Conc. H₂SO₄: Dehydrating agent (removes H₂O from sugars, sulphates). Hot concentrated H₂SO₄ = oxidising agent. Cold concentrated H₂SO₄ passivates Fe, Al (thin oxide layer).
Physical trends: F₂ (pale yellow gas), Cl₂ (greenish yellow gas), Br₂ (reddish brown liquid — only liquid non-metal at RT), I₂ (violet/purple solid — sublimes). Boiling point increases down the group.
Reactivity: Decreases down group: F > Cl > Br > I. F is most electronegative element overall. F has no d-orbitals → cannot expand octet → no positive oxidation states (unlike Cl, Br, I).
Interhalogen compounds: AB, AB₃, AB₅, AB₇ types (A = heavier halogen, B = F or Cl). ClF₃ (T-shape), IF₅ (square pyramidal), IF₇ (pentagonal bipyramidal). Stronger oxidising agents than parent halogens.
Oxoacids of Cl: HOCl (hypochlorous, Cl = +1), HClO₂ (chlorous, +3), HClO₃ (chloric, +5), HClO₄ (perchloric, +7, strongest acid among all oxoacids of Cl — acid strength increases with oxidation state).
General: Zero group / Inert gases. Completely filled outermost shell → extremely stable, do not form compounds easily. He (1s²), Ne (2s²2p⁶), Ar, Kr, Xe, Rn.
Xe compounds: Xenon forms compounds with the most electronegative elements (F, O). XeF₂ (linear, 3 lone pairs on Xe), XeF₄ (square planar, 2 lone pairs), XeF₆ (distorted octahedral, 1 lone pair), XeO₃ (pyramidal), XeOF₄ (square pyramidal).
Uses: He — airships, cryogenics. Ne — neon signs (orange-red light). Ar — inert atmosphere in welding, filling light bulbs. Kr — camera flash bulbs. Xe — high-intensity lights, anaesthesia. Rn — radioactive, used in cancer treatment (historical).
HNO₃: nitric acid, N = +5
Aqua regia: 3 HCl + 1 HNO₃
Dissolves: Au, Pt
Conc HNO₃: yellow (NO₂ dissolved)
H₃PO₃: dibasic (2 OH, 1 P-H)
H₃PO₂: monobasic (1 OH, 2 P-H)
Rule: Count only P-OH groups for basicity
P-H bond = non-ionisable
Cl₂: greenish-yellow gas
Br₂: reddish-brown liquid
I₂: shiny violet-black solid
Only liquid non-metal: Br₂
Only element subliming: I₂
XeF₄: square planar (2 lone pairs)
XeF₆: distorted octahedral (1 lone pair)
XeO₃: pyramidal
XeOF₄: square pyramidal
Bromine (Br₂) is the only liquid NON-METAL at room temperature and standard pressure. Mercury (Hg) is a liquid metal. Gallium is a metal (melts in palm). Iodine is a solid.
Halogen properties: 1 Q/year
Noble gas compounds: 1 Q every 2 years
Expected: Acid strength order of Cl oxoacids
Watch: XeF₄ shape (VSEPR)