Periodic Classification of Elements — Class 10 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 10 Science, Chemistry — Chapter 8. The periodic table and its trends — plus metallurgy (a TN-specific part of this chapter).
1. About this chapter
This chapter has two parts: (a) the modern periodic table and periodic properties, and (b) metallurgy — how metals are extracted from their ores, alloys, and corrosion.
2. The modern periodic table
- Modern periodic law: the physical and chemical properties of elements are a periodic function of their atomic number.
- The table has 7 periods (rows) and 18 groups (columns); elements are arranged by increasing atomic number.
3. Periodic properties (trends)
| Property | Across a period (left → right) | Down a group (top → bottom) |
|---|---|---|
| Atomic radius | decreases | increases |
| Ionisation energy | increases | decreases |
| Electron affinity | increases (generally) | decreases |
| Electronegativity | increases | decreases |
| Metallic character | decreases | increases |
- Atomic radius shrinks across a period (more nuclear charge), grows down a group (new shells).
- Ionisation energy is the energy to remove an electron; it rises across, falls down.
4. Metallurgy
- Mineral / ore: a mineral from which a metal can be profitably extracted is an ore.
- Basic steps: concentration of ore → roasting/calcination → reduction to metal → refining.
- Aluminium: extracted from bauxite by electrolysis of molten alumina (Hall–Héroult process).
- Copper: extracted from copper pyrites by roasting and smelting (self-reduction).
- Iron: extracted from haematite in a blast furnace (reduction by coke/CO).
- Alloys: homogeneous mixtures of metals (e.g., brass = Cu + Zn; bronze = Cu + Sn; steel = Fe + C) — made to improve strength, hardness or resistance.
- Corrosion: slow destruction of metal by air/moisture (e.g., rusting of iron, Fe₂O₃·xH₂O); prevented by galvanising, painting, oiling, alloying.
5. Worked examples
Example 1. Arrange Na, Mg, Al in order of increasing atomic radius. Across a period radius decreases → Al < Mg < Na.
Example 2. Why is aluminium extracted by electrolysis and not by reduction with carbon? Aluminium is very reactive; carbon cannot reduce its oxide, so electrolytic reduction of molten alumina is used.
Example 3. Name the alloy and constituents used in making statues/utensils that resists corrosion. Bronze (copper + tin) — harder and more corrosion-resistant than pure copper.
6. Common mistakes
- Mistake: Thinking atomic radius increases across a period. Fix: It decreases across (left→right) and increases down a group.
- Mistake: Treating every mineral as an ore. Fix: Only minerals from which metal is extracted profitably are ores.
- Mistake: Forgetting metallurgy is part of this TN chapter. Fix: Revise extraction of Al, Cu, Fe, alloys and corrosion too.
7. Practice (book-back style)
- State the modern periodic law.
- How does ionisation energy vary across a period and down a group?
- Differentiate a mineral and an ore.
- Name the ore and method of extraction of aluminium.
- What is corrosion? Give two methods to prevent rusting.
8. Answer key
- Properties of elements are a periodic function of their atomic number.
- Increases across a period; decreases down a group.
- Mineral: natural compound of a metal. Ore: a mineral from which metal is extracted profitably.
- Ore: bauxite; method: electrolysis of molten alumina (Hall–Héroult).
- Slow eating away of metal by air/moisture; prevented by galvanising and painting (also oiling, alloying).
9. Quick revision
- Chemistry Ch 8 · periodic table + metallurgy (TN-specific).
- Modern law: properties are a periodic function of atomic number.
- Across period: radius ↓, ionisation energy ↑, electronegativity ↑, metallic character ↓.
- Metallurgy steps: concentration → roasting/calcination → reduction → refining.
- Al ← bauxite (electrolysis); Cu ← copper pyrites; Fe ← haematite (blast furnace).
- Alloys: brass, bronze, steel; corrosion prevented by galvanising/painting.
