Chemistry — Metals and Non-Metals
Overview
Metals and Non-Metals is a foundational chemistry topic for KAR TET Paper II, bridging physical science concepts with everyday applications. This topic tests your understanding of how elements behave based on their electronic configuration and position in the periodic table. Questions typically appear in both content-based MCQs (identifying properties, reactions, uses) and pedagogy-linked items (how to teach these concepts effectively to Classes VI–VIII students).
Mastery requires knowing the characteristic physical and chemical properties of both categories, the reactivity series of metals, and common extraction/reaction patterns. Since upper-primary science emphasises connecting classroom learning to daily life, expect questions linking metals/non-metals to household items, tools, electrical wiring, and biological systems.
Key Concepts
- Metals are elements that lose electrons to form positive ions (cations); they are typically lustrous, malleable, ductile, and good conductors of heat and electricity. Examples: iron, copper, aluminium, gold.
- Non-metals gain or share electrons to form negative ions (anions) or covalent bonds; they are generally brittle, dull, and poor conductors. Examples: sulphur, carbon, oxygen, nitrogen.
- Metalloids (boron, silicon, germanium) show intermediate properties and are used as semiconductors—important for linking to technology in classrooms.
- Reactivity series ranks metals by their tendency to lose electrons: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au > Pt (most to least reactive).
- Displacement reactions occur when a more reactive metal displaces a less reactive metal from its compound. Example: Zn + CuSO₄ → ZnSO₄ + Cu.
- Ionic compounds form when metals react with non-metals; these have high melting points, conduct electricity when molten or dissolved, and are generally soluble in water.
- Corrosion is the gradual destruction of metals by chemical reaction with the environment (rusting of iron = Fe₂O₃·xH₂O). Prevention methods include painting, oiling, galvanisation, and alloying.
- Alloys are homogeneous mixtures of metals (or metal + non-metal) designed to enhance properties—e.g., steel (Fe + C), brass (Cu + Zn), bronze (Cu + Sn).
Formulas / Key Facts
| Concept | Key Fact / Formula |
|---|---|
| Reactivity series (top 5) | K, Na, Ca, Mg, Al — react with cold water or steam; stored in kerosene (Na, K) |
| Reactivity series (middle) | Zn, Fe, Pb — react with steam; used in galvanisation (Zn) |
| Reactivity series (bottom) | Cu, Hg, Ag, Au, Pt — do not react with water or dilute acids; found native |
| Reaction with oxygen | Metal + O₂ → Metal oxide (basic); Non-metal + O₂ → Non-metal oxide (acidic) |
| Reaction with water | 2Na + 2H₂O → 2NaOH + H₂ (vigorous); Fe + H₂O (steam) → Fe₃O₄ + H₂ |
| Reaction with acids | Zn + 2HCl → ZnCl₂ + H₂ (displacement of hydrogen) |
| Thermite reaction | 2Al + Fe₂O₃ → Al₂O₃ + 2Fe (highly exothermic; used to weld railway tracks) |
| Rusting condition | Iron + Oxygen + Water → Hydrated iron(III) oxide |
| Noble metals | Au, Pt — least reactive; resist corrosion; used in jewellery and electronics |
Worked Examples
Example 1 — Predicting displacement
Problem: Will copper displace zinc from zinc sulphate solution?
Solution:
- Check reactivity series: Zn is above Cu.
- A less reactive metal (Cu) cannot displace a more reactive metal (Zn).
- Answer: No reaction occurs.
Example 2 — Identifying metal vs non-metal
Problem: Element X is brittle, does not conduct electricity, and forms an acidic oxide. Is X a metal or non-metal?
Solution:
- Brittle → not malleable/ductile (non-metal trait).
- Poor conductor → non-metal trait.
- Acidic oxide → non-metals form acidic oxides (e.g., SO₂ + H₂O → H₂SO₃).
- Answer: X is a non-metal.
Example 3 — Writing a balanced equation
Problem: Magnesium ribbon burns in air. Write the balanced equation and name the product.
Solution:
- Magnesium reacts with oxygen: Mg + O₂ → MgO (unbalanced).
- Balance: 2Mg + O₂ → 2MgO.
- Product: Magnesium oxide (basic oxide, white powder).
Common Mistakes
| Wrong Thinking | Correct Fix |
|---|---|
| "All metals are solid." | Mercury (Hg) is a liquid metal at room temperature. |
| "Hydrogen is a metal because it is in group 1." | Hydrogen is a non-metal; its position is due to single valence electron, but it gains/shares electrons like non-metals. |
| "Gold does not react, so it is not a metal." | Gold is a metal but a noble metal—extremely low reactivity does not negate metallic character. |
| "Reactivity series applies only to reactions with acids." | It applies to reactions with water, oxygen, and displacement of other metals as well. |
| "Carbon is always a non-metal and never conducts electricity." | Graphite (an allotrope of carbon) conducts electricity due to delocalised electrons—an exception students must know. |
Quick Reference
- Sonorous: Metals produce a ringing sound when struck; non-metals do not.
- Malleability & Ductility: Metals can be beaten into sheets (malleable) and drawn into wires (ductile).
- Reactivity series mnemonic: "Please Stop Calling Me A Cute Zebra, I Like Hyenas Copper More Silver Gold Platinum" (K-Na-Ca-Mg-Al-Zn-Fe-Pb-H-Cu-Hg-Ag-Au-Pt).
- Galvanisation: Coating iron with zinc to prevent rusting.
- Anodising: Coating aluminium with a thick oxide layer for corrosion resistance.
- Exception to remember: Diamond (carbon) is the hardest natural substance; graphite (carbon) is soft and conducts electricity—both are non-metals.