Chapter 7 • Class 8 Science
⚗️ Particulate Nature of Matter
Curiosity — Textbook of Science for Grade 8
📋 Table of Contents
7.1 What Is Matter Composed Of?
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Fig: Chalk → powder
still chalk!
still chalk!
Break chalk → grind → still chalk! Sugar dissolves in water — you can't see it but you can taste it. What does this tell us?
- All matter is made of extremely small particles
- These particles are too small to see even with a microscope!
- Sugar breaks into particles → occupies spaces between water particles
📌 Key Definitions
Constituent Particle = The basic unit that makes up a substance/material (cannot be broken further by physical means).
Interparticle Spaces = The spaces (gaps) that exist between particles of matter. Sugar particles fit into spaces between water particles when dissolved!
Interparticle Spaces = The spaces (gaps) that exist between particles of matter. Sugar particles fit into spaces between water particles when dissolved!
Acharya Kanad — India's Ancient Genius!
Ancient Indian philosopher Acharya Kanad first proposed the idea of Parmanu (atom) — tiny, indivisible, eternal particles that make up matter. Written in his work Vaisheshika Sutras. 🇮🇳✨
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Fig: Dissolving sugar
in water
in water
When sugar dissolves in water, the water remains sweet throughout even in the top layer. Why?
- Sugar breaks into constituent particles
- Particles occupy interparticle spaces between water particles
- Particles are present everywhere → top tastes sweet too!
- This is why ocean water tastes salty even though we can't see salt
📌 Interparticle Attraction
Constituent particles are held together by attractive forces called interparticle attractions. The strength of these forces determines the physical state of a substance (solid/liquid/gas).
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7.2.1 Solid State
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Fig: Solid objects —
nail, salt, stone, wood
nail, salt, stone, wood
- Particles tightly packed in fixed positions
- Interparticle attraction MAXIMUM 💪
- Particles only vibrate — cannot move past each other
- Definite shape AND volume
- Cannot be compressed easily
- Interparticle space is minimum
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Fig: Solid → vibration
increases → Liquid
increases → Liquid
What happens when a solid is heated?
- Particles vibrate more vigorously
- Vibrations become so strong → particles leave fixed positions
- Interparticle attraction weakens → solid becomes liquid!
📌 Key Definition
Melting Point = The minimum temperature at which a solid melts to become a liquid at atmospheric pressure.
Ice = 0°C | Urea = 133°C | Iron = 1538°C
Ice = 0°C | Urea = 133°C | Iron = 1538°C
| Material | Melting Point | Why? |
|---|---|---|
| 🧊 Ice | 0°C | Weak interparticle forces |
| 🧪 Urea | 133°C | Moderate forces |
| 🔩 Iron | 1538°C | Very strong interparticle forces |
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7.2.2 Liquid State
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Fig: Water takes shape
of any container!
of any container!
- Particles loosely packed — free to move
- Interparticle attraction slightly weaker than solids
- NO fixed shape — takes shape of container
- Definite volume — 200 mL stays 200 mL in any container!
- Particles move within limited space
- Liquids and gases = Fluids (both flow!)
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Fig: Finger moves
through water easily
through water easily
You can move your finger through water but NOT through a solid. Why?
- Liquid particles are free to move → they temporarily separate for the finger
- As finger moves out → particles return → no permanent cut
- This proves liquid interparticle forces are weaker than in solids
📌 Key Definition
Boiling Point = The temperature at which a liquid boils and turns into vapour at atmospheric pressure.
Evaporation = Slow vapour formation at ALL temperatures (only at surface). Happens even below boiling point!
Evaporation = Slow vapour formation at ALL temperatures (only at surface). Happens even below boiling point!
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7.2.3 Gaseous State
- Particles completely free to move in all directions
- Interparticle attraction is negligible (nearly zero)
- NO fixed shape AND NO fixed volume
- Gas fills up the entire available space
- Interparticle spacing is MAXIMUM
- Gases are easily compressible (unlike liquids and solids)
Smoke Experiment Proves It!
Fill smoke in jar A → place jar B on top → remove glass plate → smoke fills ENTIRE jar B! Gas particles move freely and occupy all available space. 🫙→🌫️
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7.3 Interparticle Spacing in Three States
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Fig: Air compresses
in syringe!
in syringe!
Syringe experiment proves gases are compressible:
- Block syringe opening → push plunger → air compresses!
- Gas particles are far apart → can be pushed together
- Release plunger → gas expands back
- Try with water → water is incompressible!
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Fig: Sugar dissolves →
water level drops!
water level drops!
Sugar + Water → after dissolving, water level is BELOW original mark!
- Sugar particles fit into spaces between water particles
- Volume of solution < Volume of water + Volume of sugar
- Proves: there ARE spaces between liquid particles!
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7.4 How Particles Move in Different States
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Fig: Fragrance spreads
in whole room!
in whole room!
Drop potassium permanganate in water → pink colour spreads throughout! 🩷 Burn incense → fragrance fills entire room! Why?
- Particles of matter are in constant motion
- They spread out on their own — called Diffusion
- Hot water → KMnO₄ spreads fastest
- Room temp water → spreads slower
- Ice cold water → spreads slowest
- More heat = faster particle movement!
📌 Key Concept
The movement of particles increases with increase in temperature (heat energy).
Thermal energy determines how fast particles move → which determines the physical state of matter!
Thermal energy determines how fast particles move → which determines the physical state of matter!
Why Does Soap Clean Oil?
Soap particles have two ends: one attaches to oil, other mixes with water. Soap particles surround oil particles on fabric and help lift the oil away. The particulate nature of matter at work! 🫧
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States of Matter — Full Comparison
SOLID
- ✅ Fixed shape
- ✅ Fixed volume
- 🔒 Particles tightly packed
- 💪 Max attraction
- 📦 Min spacing
- 🔄 Only vibrate
- ❌ Incompressible
LIQUID
- ❌ No fixed shape
- ✅ Fixed volume
- 🔓 Loosely packed
- ↕️ Weaker attraction
- 📐 More spacing
- 🏃 Move (limited)
- ❌ Incompressible
GAS
- ❌ No fixed shape
- ❌ No fixed volume
- 🆓 Completely free
- ≈0 Negligible
- 🌌 Max spacing
- 🚀 Move freely
- ✅ Compressible
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Fig: Particle arrangement in Solid, Liquid & Gas
| Property | 🧱 Solid | 💧 Liquid | 💨 Gas |
|---|---|---|---|
| Shape | Fixed ✅ | Not fixed ❌ | Not fixed ❌ |
| Volume | Fixed ✅ | Fixed ✅ | Not fixed ❌ |
| Interparticle Space | Minimum | Medium | Maximum |
| Attraction | Maximum 💪 | Medium | Negligible ≈0 |
| Movement | Only vibrate | Limited | Freely everywhere |
| Compressibility | ❌ No | ❌ No | ✅ Yes |
Thermal Energy = Key to States!
It is the thermal (heat) energy of particles that determines the physical state of matter. More heat → faster particles → weaker attraction → changes state from solid → liquid → gas!
What are constituent particles made of?
The tiny constituent particles of matter are atoms and molecules. Iron → iron atoms. Water → H₂O molecules (2 hydrogen + 1 oxygen atoms). You'll learn more in higher grades!
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📸 Quick Revision Snapshots
Matter is made of extremely small constituent particles that cannot be seen even through ordinary microscopes.
Particles are held by interparticle attractive forces. Strength of forces determines the physical state.
Solid = tightly packed, max attraction, fixed shape & volume, only vibrate, min spacing.
Liquid = loosely packed, weaker attraction, no fixed shape but fixed volume, moves in limited space.
Gas = negligible attraction, no fixed shape or volume, max spacing, moves freely everywhere. Compressible!
Melting point = solid → liquid. Boiling point = liquid → gas. Evaporation = slow conversion at all temperatures.
Particles are in constant motion. More heat = faster movement. Gas particles spread fastest (diffusion).
Sugar dissolves in water → fits into interparticle spaces. Water level drops after dissolving = proves spaces exist!
✨ Notes by @edugrown — Happy Learning! ✨