Patterns in the Periodic Table
This topic explains periodic trends and group properties in the Periodic Table. It covers element arrangement by increasing proton number, electronic configuration, valence electrons, metallic and non-metallic character trends, and characteristic properties of Group 1 alkali metals, Group 17 halogens, Group 18 noble gases, and transition metals. It also includes the reactivity series, displacement and thermal decomposition reactions, and rust prevention methods.
1. Periodic Trends
- 🔹 Arrangement of Elements: Elements are arranged by increasing proton number, resulting in periodic recurrence of chemical properties. Periods are rows; groups are columns with same number of valence electrons.
- 🔹 Electronic Configuration and Position: Group number shows number of valence electrons; period number shows number of shells. Similar configurations in a group lead to similar properties.
- 🔹 Valence Electrons and Ionic Charge: Group number helps predict ionic charge. Group I forms +1 ions, Group VII forms –1 ions.
- 🔹 Trends Across Period: Across a period, atomic number increases, metallic character decreases, and non-metallic character and electronegativity increase.
- 🔹 Trends Down Group: Down a group, atomic size and metallic character increase. Reactivity trend depends on group: Group I becomes more reactive, Group VII less reactive.
- 🔹 Prediction of Group Properties: Trends help predict melting/boiling points, reactivity, and appearance of Group 1 and Group 17 elements.
2. Group Properties
- 🔹 Group 1 Alkali Metals: Soft, low-density metals with low melting points that decrease down the group. Reactivity with water increases down the group, forming hydroxide and hydrogen gas.
- 🔹 Group 17 Halogens: Diatomic reactive non-metals. Melting/boiling points increase down the group, while reactivity decreases. More reactive halogens displace less reactive ones in solution.
- 🔹 Group 18 Noble Gases: Unreactive, monatomic gases with full outer electron shells. Low boiling points (increase down group). Used to provide inert atmospheres.
- 🔹 Important Reaction: Cl₂(g) + 2NaBr(aq) → 2NaCl(aq) + Br₂(aq)
3. Transition Elements
- 🔹 Properties: High melting points, high density, form coloured compounds, variable oxidation states.
- 🔹 Catalytic Use: Act as catalysts, e.g. iron in Haber Process, manganese(IV) oxide in decomposition of hydrogen peroxide.
4. Reactivity Series
- 🔹 Order of Reactivity: Potassium > Sodium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > Copper > Silver.
-
🔹 Reactions with Water/Steam/Acid:
- ▪️ Water: Potassium and sodium react violently; copper does not react.
- ▪️ Steam: Magnesium forms magnesium oxide (MgO).
- ▪️ Dilute Acids: Zinc reacts moderately; lead does not react due to insoluble PbCl₂.
- 🔹 Displacement Reactions: More reactive metals displace less reactive ones from their salt solutions. E.g. Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag.
- 🔹 Thermal Stability of Carbonates: Reactive metals form stable carbonates. Less reactive ones decompose to metal oxide and CO₂.
-
🔹 Metal Extraction:
- ▪️ Reactive metals (e.g., aluminium) require electrolysis.
- ▪️ Less reactive metals (e.g., iron, zinc) are extracted by carbon reduction.
-
🔹 Iron Extraction and Rust Prevention:
- ▪️ Haematite (Fe₂O₃) is reduced using carbon monoxide. Limestone removes impurities as slag (CaSiO₃).
- ▪️ Rusting requires water and oxygen. Prevented by barrier protection (paint, oil) or sacrificial protection (zinc or magnesium).
-
Reactive metals and water: 2Na + 2H₂O → 2NaOH + H₂ -
Halogen displacement: Cl₂(g) + 2NaBr(aq) → 2NaCl(aq) + Br₂(aq) -
Metal displacement: Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s) -
Carbonate thermal decomposition: CuCO₃(s) → CuO(s) + CO₂(g) -
Iron extraction from iron ore: Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g) -
Rust formation: 4Fe(s) + 3O₂(g) + 2H₂O(l) → 2Fe₂O₃·H₂O(s)
- ⚠️ Assuming all metals are hard – Group I metals are soft.
- ⚠️ Thinking all non-metals are gases – iodine is a solid, bromine is a liquid.
- ⚠️ Confusing group number with period number when assigning electronic configurations.
- ⚠️ Assuming noble gases are reactive like oxygen – they are actually inert.
- 👉 Be able to identify group and period using proton number or electronic configuration.
- 👉 Explain trends across periods and down groups, including reactivity, boiling points, and metallic character.
- 👉 Memorise and compare properties of Group 1, 17, 18, and transition metals.
- 👉 Describe halogen displacement reactions using reactivity trends.
- 👉 Recognise transition metal features: variable charges, coloured compounds, catalytic functions.