๐ Class 7 Science Curiosity – Chapter 4 Notes
๐งฒ The World of Metals and Non-metals | Amresh Academy
๐ Introduction
These have different physical and chemical properties which decide their uses.
⚙️ 1. Properties of Metals
๐จ Malleability
๐ Ability to be beaten into thin sheets
- ๐ช Metals → Malleable (copper, aluminium, iron)
- Examples: Aluminium foil, silver foil
❌ Non-metals → Brittle (coal, sulfur)
⚠️ Exceptions:
- Sodium & Potassium → Soft metals
- Mercury → Liquid metal
๐ Ductility
๐ Ability to be drawn into wires
- Metals → Copper, aluminium, gold
- Used in electrical wires
๐ Sonority
๐ Ability to produce ringing sound
- Metals → Sonorous (bells, ghungroos) ๐
- Non-metals → Dull sound
๐ฅ Conduction of Heat
- Metals → Good conductors (cooking utensils) ๐ณ
- Non-metals → Poor conductors (wooden handles)
⚡ Conduction of Electricity
- Metals → Good conductors (copper wires)
- Non-metals → Poor conductors (plastic, rubber)
๐ง️ 2. Effect of Air and Water on Metals (Iron)
๐งฑ Rusting
๐ Formation of brown layer (rust) on iron
Conditions:
- Air + Water
⚠️ Corrosion
๐ Slow damage of metals
Examples:
- Copper → Green coating
- Silver → Black coating
๐ก️ Prevention Methods:
- ๐จ Painting
- ๐ข️ Oiling/Greasing
- ๐งช Galvanisation (zinc coating)
๐️ Interesting Fact:
๐ Iron Pillar of Delhi has not rusted for 1600+ years
๐ฅ 3. Effect on Other Metals
๐ฅ Magnesium
- Burns with bright white flame
- Forms magnesium oxide
⚡ Sodium
- Highly reactive
- Stored in kerosene
๐ฟ 4. Non-metals
๐ Properties:
- ❌ Non-lustrous
- ❌ Soft & brittle
- ❌ Non-ductile
- ❌ Non-sonorous
- ❌ Poor conductors
๐งช Examples:
- Sulfur
- Phosphorus
- Oxygen
- Carbon
- Nitrogen
๐ฅ Sulfur:
- Burns → forms sulfur dioxide (acidic)
๐ง Phosphorus:
- Stored in water๐ Prevents reaction with air
๐ 5. Importance of Non-metals
- ๐ฌ️ Oxygen → Respiration
- ๐งฌ Carbon → Life molecules
- ๐ฑ Nitrogen → Fertilisers
- ๐ง Chlorine → Water purification
- ๐ฉน Iodine → Antiseptic
๐ Key Differences
Feature | Metals ๐ช | Non-metals ๐ฟ |
Appearance | Lustrous ✨ | Dull |
Nature | Hard | Soft/Brittle |
Malleability | Yes | No |
Ductility | Yes | No |
Sound | Sonorous ๐ | Non-sonorous |
Conductivity | Good ⚡ | Poor |
Oxides | Basic | Acidic |
๐ Final Summary
๐ Metals:
- Strong, shiny, conductive ⚡
- Used in tools, utensils, machines
๐ Non-metals:
- Essential for life ๐ฑ
- Used in medicines, fertilisers
