The complete lecture — the periodic trends and the Contact-process reactor come alive in the live panel as you read. Scroll down; the animation keeps pace, and you can run the reactor yourself.
1 — Periodic classification & trends
- Representative elements — the s- and p-block (main-group) elements; their valence shell is being filled.
Across a period: radius decreases, ionization energy increases (higher nuclear charge, same shell). Down a group the opposite, as a new shell is added each row.
2 — The s-block (IA & IIA)
Alkali metal + water2Na + 2H₂O → 2NaOH + H₂↑ (vigorous, alkaline)
Group IA (ns¹) and IIA (ns²): reactive metals forming M⁺ / M²⁺. Reactivity rises down each group; flame colours (Na yellow, K lilac, Ca brick-red) identify them.
3 — The p-block families
| Group | Family |
|---|
| IIIA | boron family |
| IVA | carbon family |
| VA | nitrogen family |
| VIA | oxygen family |
| VIIA | halogens |
| VIIIA | noble gases |
The first member of each group (B, C, N, O, F) is anomalous — small, very electronegative, with no available d-orbitals.
4 — The anomalous position of hydrogen
- Hydrogen (1s¹) — resembles Group IA (one valence electron, forms H⁺) and Group VIIA (needs one electron, forms H⁻, diatomic H₂). It has a unique position.
5 — Inert-pair effect & diagonal relationship
- Inert-pair effect — the outer ns² pair resists bonding in heavy p-block elements, so the lower (group−2) state is more stable (e.g. Pb²⁺ > Pb⁴⁺).
The diagonal relationship (Li–Mg, Be–Al, B–Si) arises from a near-equal charge-to-radius ratio.
6 — The Contact process (sulphuric acid)
Key step2SO₂ + O₂ ⇌ 2SO₃ ΔH = −196 kJ (exothermic) · V₂O₅ catalyst
Stages: S→SO₂→SO₃→(oleum)→H₂SO₄. Conditions ~450 °C (compromise), 1–2 atm (fewer gas moles), excess air, V₂O₅ catalyst. Move the sliders to see the yield respond.
7 — Uses of sulphuric acid
- Fertilisers (its biggest use), car batteries, detergents, dyes, pickling steel, drying agent.
8 — Exam recap
- Periodic classification & the five trends (with reasons).
- s-block reactions, flame colours & trends.
- p-block families & the first-member anomaly.
- Hydrogen's position; inert-pair effect; diagonal relationship.
- The Contact process: stages, conditions & uses of H₂SO₄.