Class 10 CBSE – Science
Topic: Metals & Non‑Metals
Objective – Understand what makes an element a metal or a non‑metal, learn their common properties, and be able to classify elements accordingly.
1. Simple Explanation
| Term | What it is | Key Idea |
|---|---|---|
| Metal | Elements that are good conductors of electricity & heat, usually shiny, heavy and malleable (can be hammered into sheets). | Their outer electrons are loosely bound, allowing them to move freely. |
| Non‑metal | Elements that are poor conductors, brittle (if solid) and usually have low density. | Their outer electrons are tightly held, so they do not conduct well. |
| Metalloid | Elements that have a mix of metal & non‑metal properties (e.g., silicon). | Often found on the boundary between metals & non‑metals on the periodic table. |
Why the difference?
It comes from how strongly the outer (valence) electrons are bound to the nucleus and how the atoms are arranged in the solid. Metals have a "sea of electrons" that move freely, whereas non‑metals have electrons tightly localized.
2. Key Points
2.1 General Properties
| Property | Metals | Non‑Metals |
|---|---|---|
| Appearance | Shiny (metallic luster) | Dull, opaque, sometimes translucent |
| Density | High | Low |
| Malleability & Ductility | High (can be hammered or drawn into wires) | Low (brittle) |
| Conductivity | Excellent (electricity & heat) | Poor |
| Melting & Boiling Points | Usually high | Usually low (except some like sulfur) |
| Oxidation | Friendly with oxygen → oxides (e.g., Fe₂O₃, rust) | Less reactive; when they react, they form non‑metal oxides (e.g., CO₂, H₂O) |
| Acid–Base Behaviour | Basic oxides, hydroxides (e.g., NaOH, Ca(OH)₂) | Acidic oxides, often neutral (e.g., CO₂, SO₂) |
2.2 Physical Properties of Metals
| Property | Typical Values | Why |
|---|---|---|
| Electrical Conductivity | > 10⁶ S/m | Free electrons |
| Thermal Conductivity | > 50 W/m·K | Free electrons also carry heat |
| Phase at Room Temperature | Solid (except mercury) | High melting points |
| Colour | Usually silver, white or gray | Metallic bonding gives shiny appearance |
2.3 Physical Properties of Non‑Metals
| Property | Typical Values | Why |
|---|---|---|
| Electrical Conductivity | < 10⁻⁸ S/m | Electrons are localized |
| Thermal Conductivity | < 2 W/m·K | No free electrons |
| Phase at Room Temperature | Solid, liquid or gas | Low melting points |
| Colour | Varies: black (e.g., carbon), white (e.g., sulfur) | No metallic luster |
2.4 Chemical Properties
| Behaviour | Metals | Non‑Metals |
|---|---|---|
| Reaction with water | Often react (e.g., Na + 2 H₂O → NaOH + H₂) | Generally inert, but some (e.g., Cl₂) react violently |
| Reaction with acids | Form salts + H₂ gas | Often form salts, sometimes no gas |
| Reaction with bases | Form metal hydroxides | Form acid or no reaction |
2.5 Classification on the Periodic Table
- Metals – Left side & center (s‑, p‑block low‑energy levels)
- Metalloids – Diagonal stripe (e.g., Si, Ge)
- Non‑Metals – Right side (p‑block high‑energy levels)
3. Worked Example
Problem
Classify the following elements as metal, metalloid, or non‑metal:
- Aluminium
- Silicon
- Sulphur
- Potassium
- Graphite
- Boron
Solution
| Element | Key Properties | Classification |
|---|---|---|
| Aluminium | Good conductor, shiny, malleable, forms Al₂O₃ | Metal |
| Silicon | Brittle solid, semi‑conductor, appears grey | Metalloid |
| Sulphur | Brittle, yellow, low melting point, reacts with acids | Non‑Metal |
| Potassium | Soft, high reactivity with water, reacts with oxygen | Metal |
| Graphite | Conductive, layered structure, appears black | Metal (though sometimes called a metalloid; but in CBSE it's considered a metal due to its good conductivity) |
| Boron | Brittle, forms covalent network, reacts slowly with acid | Metalloid |
Explanation
- Metals: Aluminium, Potassium, Graphite (good conductivity, malleability).
- Metalloids: Silicon, Boron (mix of properties).
- Non‑Metal: Sulphur (low density, brittle, reactive with acids).
4. Quick Revision Summary
- Metals – shiny, dense, malleable, good conductors, basic oxides.
- Non‑Metals – dull, low density, brittle, poor conductors, acidic oxides.
- Metalloids – intermediate properties; often used as semiconductors.
- Typical metal reactions: +O₂ → oxides; +H₂O →