IP Chemistry Upper Sec 08: Patterns in the Periodic Table

These notes align with SEAB GCE O-Level Chemistry (6092) content used in IP programmes (exams from 2026).

Status: SEAB O-Level Chemistry 6092 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.

The core idea is simple: Periodic-table patterns come from proton number and valence electrons.

Use it as a working check: Period tells you shell number. Group tells you valence electrons and common ion behaviour. Trends then explain reactivity, oxide character, and displacement.

Then go one layer deeper: Example: chlorine displaces bromide because chlorine is the more reactive halogen, but iodine cannot displace chloride from a chloride solution.

What you must know

• Elements arranged by increasing proton number; period number = number of shells, group number = valence electrons → common ion charge and metallic vs non-metallic character.
• Across a period: metallic to non-metallic; basic oxides → amphoteric → acidic; ionic → giant covalent → simple molecular structures.
• Group 1: soft, low density, mp decreases down group; react with water to form hydroxide + hydrogen (fizzing, floats, lilac flame for K). Down the group reactivity increases.
• Group 17: coloured diatomic molecules (F₂ pale yellow gas, Cl₂ greenish-yellow gas, Br₂ red-brown liquid, I₂ purple solid); reactivity decreases down group; halogen displacement reactions follow reactivity.
• Group 18: full valence shell → very unreactive; uses for inert atmosphere (argon in lamps, helium in balloons).
• Transition elements: higher mp/density than Group 1, variable oxidation states, coloured compounds/ions, good catalysts (Fe in Haber, Ni in hydrogenation).
• Reactivity series: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Ag; predict reactions with water/steam/acid, displacement, reduction of oxides, thermal stability of carbonates (Group 1 most stable).
• Rusting of iron requires oxygen + water; accelerated by salts/acids. Prevention: barrier (paint/oil/plastic), galvanising, sacrificial protection (Mg/Zn).

Detailed notes

• Across a period: increasing nuclear charge with similar shielding → atomic radius decreases, ionisation energy generally rises; metallic to non-metallic character decreases; oxides shift basic → amphoteric → acidic. Structures: metals (Na–Al) metallic, Si giant covalent, P/S/Cl simple molecular, Ar monoatomic.

Group trend cause checkpoint

Before memorising the direction of a trend, decide whether the element is trying to lose or gain electrons.