The Periodic Table
Groups I, VII, noble gases, transition metals, and periodic trends
The Periodic Table arranges elements by atomic number. Elements in the same group have the same number of outer electrons and similar chemical properties. Elements in the same period have the same number of electron shells.
Group I — Alkali Metals (Li, Na, K): Very reactive, stored in oil. React vigorously with water → metal hydroxide + hydrogen. Reactivity increases down the group (outer electron is further from nucleus, easier to lose).
Group VII — Halogens (F, Cl, Br, I): Diatomic molecules (Cl₂). React with metals to form salts. Reactivity decreases down the group (harder to gain an electron as atom gets larger). More reactive halogen displaces less reactive one.
Group VIII/0 — Noble Gases (He, Ne, Ar): Full outer shells → very unreactive. Used in lighting, welding, balloons.
Transition Metals (Fe, Cu, Cr): Coloured compounds, variable oxidation states, good catalysts (iron in Haber process, vanadium pentoxide in Contact process).
Trends across a period: Metallic character decreases left→right. Oxides go from basic (metals) to acidic (non-metals).
Key Points to Remember
- 1Group I: reactivity increases down group
- 2Group VII: reactivity decreases down group
- 3Noble gases: full outer shells, unreactive
- 4Transition metals: coloured compounds, catalysts
Pakistan Example
Sodium Streetlights and Neon Signs — Groups in Karachi
The yellowish-orange glow of old street lights across Pakistan comes from sodium (Group I). Neon signs in Saddar use noble gases. The iron (transition metal) in Karachi's construction uses iron's catalytic and structural properties.