Chapter Guide
Chapter Overview
1. What Is Matter Composed Of?
- All matter is composed of a large number of extremely small constituent particles.
- A constituent particle is the basic unit that makes up a larger piece of a substance or material.
- Breaking or grinding a substance into smaller pieces does not necessarily change it into a new substance. For example, grinding chalk into powder is a physical change.
- When sugar dissolves in water, its particles separate and spread throughout the water. They cannot be seen but can be detected by taste.
- The spaces between the particles of matter are called interparticle spaces.
- Even very small grains of sand and clay consist of numerous constituent particles.
Example: Sugar disappears when dissolved in water, but it remains present in the solution as tiny particles.
2. What Decides Different States of Matter?
The physical state of matter depends mainly on the arrangement of its particles, the interparticle attractions, the distance between particles and their thermal energy.
- Interparticle attractions: Attractive forces that hold the constituent particles of matter together.
- The strength of these forces depends on the nature of the substance and the distance between its particles.
- Even a slight increase in interparticle distance can drastically decrease the attractive forces.
- Thermal energy affects particle movement and helps determine the physical state of matter.
Scientific Heritage: Acharya Kanad proposed the idea of Parmanu, describing matter as being made up of tiny, indivisible and eternal particles. His ideas were written in the Vaisheshika Sutras.
3. Solid State
- Solids have a definite shape and definite volume.
- Their constituent particles are tightly packed, with minimum interparticle spacing.
- Interparticle attractions are very strong.
- Particles remain in fixed positions and cannot move freely past one another.
- They can only vibrate or oscillate about their fixed positions.
- Solids are generally difficult to compress because their particles are closely packed.
Examples: Iron, stone, wood, rock salt and aluminium.
Melting of Solids
When a solid is heated, its particles vibrate more vigorously. At a certain temperature, the particles begin to leave their fixed positions, and the solid changes into a liquid.
Melting point: The minimum temperature at which a solid melts to become a liquid at atmospheric pressure.
Examples of melting points:
- Ice – 0 °C
- Urea – 133 °C
- Iron – 1538 °C
Solids with weaker interparticle attractions generally have lower melting points, while those with stronger attractions generally have higher melting points.
4. Liquid State
- Liquids have a definite volume but no fixed shape.
- They take the shape of the container in which they are kept.
- Their particles are slightly farther apart than those in most solids.
- Interparticle attractions are weaker than in solids but still keep the particles close together.
- Particles can move freely within a limited space and move past one another.
- Liquids can flow and are practically incompressible.
Examples: Water, milk and glycerin.
Important observation: When the same quantity of water is transferred between differently shaped containers, its shape changes but its volume remains approximately the same.
Boiling and Evaporation
Boiling point: The temperature at which a liquid boils and changes into vapour at atmospheric pressure.
- During boiling, particles gain sufficient energy to overcome attractive forces and escape into the gaseous state.
- Boiling occurs throughout the liquid, producing bubbles, and vapour formation is rapid.
- Evaporation is the slower process of vapour formation that occurs at the surface of a liquid.
- Evaporation can occur at temperatures below the boiling point.
Example: Spilled water gradually disappears because of evaporation, even without reaching its boiling point.
5. Gaseous State
- Gases have no definite shape and no definite volume.
- They take the shape of their container and occupy all the available space.
- Their particles are very far apart, with maximum interparticle spacing.
- Interparticle attractions are negligible.
- Particles move freely in all directions.
- Gases are easily compressible because of the large spaces between their particles.
Examples: Air, oxygen, methane and water vapour.
Important observation: Smoke spreads throughout connected gas jars because gas particles move freely and occupy the available space.
Fluids
Fluids are substances that can flow and do not retain a fixed shape. Both liquids and gases are classified as fluids.
6. Interparticle Spacing in the Three States of Matter
The spacing between constituent particles differs in solids, liquids and gases.
| Property |
Solid |
Liquid |
Gas |
| Interparticle spacing |
Minimum |
More than in most solids |
Maximum |
| Arrangement |
Closely packed |
Less closely packed |
Far apart |
| Attractive forces |
Very strong |
Weaker than in solids |
Negligible |
| Particle movement |
Vibrations about fixed positions |
Movement within limited space |
Free movement in all directions |
| Shape |
Definite |
No fixed shape |
No fixed shape |
| Volume |
Definite |
Definite |
No fixed volume |
| Compressibility |
Very low |
Very low |
High |
Note: Ice is an exception to the general comparison of particle spacing: its particles are farther apart than those in liquid water.
7. How Particles Move in Different States of Matter
- Constituent particles of matter are in constant motion.
- In solids, particles mainly vibrate about their fixed positions.
- In liquids, particles move within a limited space and can move past one another.
- In gases, particles move freely in all directions and spread throughout the available space.
- Providing heat increases the movement of particles.
Diffusion
Diffusion is the spreading and mixing of particles from one region into another due to their constant motion.
Examples:
- Potassium permanganate spreads through water, producing a uniform pink colour.
- The fragrance of an incense stick spreads throughout a room.
- The particles of gases mix easily because they move freely and have large interparticle spaces.
Effect of Temperature on Particle Movement
Particles move faster when heated and slower when cooled.
- In hot water, potassium permanganate spreads the fastest.
- In water at room temperature, it spreads more slowly.
- In ice-cold water, it spreads the slowest.
Thus, increasing thermal energy increases particle movement.
8. How Thermal Energy Changes the State of Matter
The physical state of matter changes when the thermal energy of its particles changes sufficiently to alter their movement and the effect of interparticle attractions.
- Solid: Particles have relatively low thermal energy and remain close together, vibrating about fixed positions.
- Melting: On heating, particles gain energy and begin to move away from their fixed positions, changing the solid into a liquid.
- Liquid: Particles can move around within a limited space while remaining relatively close together.
- Boiling: Particles gain enough energy to overcome attractive forces and escape into the gaseous state.
- Gas: Particles have sufficient energy to move freely in all directions, with negligible attractive forces.
Sequence of changes on heating:
Solid → Liquid → Gas
Example: Ice melts into water, and water changes into water vapour on boiling.
9. Everyday Applications of the Particulate Nature of Matter
- Dissolving sugar: Sugar particles separate and occupy spaces between water particles.
- Ocean water: Dissolved salt particles are present even though they cannot be seen.
- Perfume and incense: Fragrance particles spread through moving air particles.
- Washing clothes: Soap particles help remove oil by interacting with oil and water.
- Gas compression: Air can be compressed because gas particles have large spaces between them.
- Flowing liquids: Milk or water spreads when spilled because its particles can move past one another.
10. Atoms and Molecules
The tiny particles that make up matter are atoms and molecules.
- Atoms: Basic particles of elements. For example, iron is made up of iron atoms.
- Molecules: Particles formed when atoms combine. For example, two hydrogen atoms combine to form a hydrogen molecule.
- A water molecule consists of two hydrogen atoms and one oxygen atom (H2O).
- Atoms of some elements, such as hydrogen, oxygen and sulfur, combine to form molecules rather than existing independently under ordinary conditions.
11. Important Points to Remember
- Matter is composed of extremely small constituent particles.
- Particles are held together by interparticle attractions.
- The strength of attraction is generally greatest in solids, weaker in liquids and negligible in gases.
- Solids: Definite shape and volume.
- Liquids: Definite volume but no fixed shape.
- Gases: No definite shape or volume.
- Interparticle spacing is generally minimum in solids, greater in liquids and maximum in gases.
- Particles move constantly, and their movement increases when heat is supplied.
- Melting changes a solid into a liquid, while boiling changes a liquid into vapour.
- Evaporation occurs at the surface of a liquid and can take place below its boiling point.
- Liquids and gases are called fluids because they can flow.
- Diffusion explains the spreading of fragrance and the mixing of particles.
Learn Clearly
Important Concepts and notes
1. Particulate Nature of Matter
- All matter is made up of extremely small particles called constituent particles.
- These particles are the basic building blocks of a substance.
- Particles of matter are held together by interparticle attractions.
- Particles have spaces between them, called interparticle spaces.
- Particles of matter are in constant motion.
Example: Sugar dissolves in water, but it does not disappear. Its tiny particles spread throughout the water.
2. Interparticle Attractions
- Interparticle attractions are the forces that hold the particles of matter together.
- These forces depend on the nature of the substance and the distance between its particles.
- As the distance between particles increases, the attractive forces decrease.
- The strength of these forces helps determine the physical state of matter.
Remember: Attractive forces are generally strongest in solids, weaker in liquids and negligible in gases.
3. Solid State
- Solids have a definite shape and definite volume.
- Their particles are tightly packed, with minimum interparticle spacing.
- Interparticle attractions are very strong.
- Particles remain in fixed positions and can only vibrate about those positions.
- Solids are generally difficult to compress.
Examples: Iron, stone, wood and aluminium.
Important: Solids have small spaces between their particles, but these spaces are not filled with air.
4. Melting and Melting Point
- Melting: The process in which a solid changes into a liquid on heating.
- Heating increases the vibrations of particles in a solid.
- At the melting point, particles begin to leave their fixed positions.
- Melting point: The minimum temperature at which a solid melts into a liquid at atmospheric pressure.
Examples of melting points:
- Ice – 0 °C
- Urea – 133 °C
- Iron – 1538 °C
5. Liquid State
- Liquids have a definite volume but no fixed shape.
- They take the shape of the container in which they are kept.
- Their particles are less closely packed than those in most solids.
- Particles can move past one another within a limited space.
- Interparticle attractions are weaker than in solids but still keep the particles close together.
- Liquids can flow and are practically incompressible.
Examples: Water, milk and glycerin.
Remember: A liquid changes its shape when poured into another container, but its volume remains approximately the same.
6. Boiling and Evaporation
- Boiling: The process in which a liquid changes into vapour at its boiling point.
- Boiling point: The temperature at which a liquid boils and changes into vapour at atmospheric pressure.
- During boiling, vapour forms rapidly throughout the liquid, producing bubbles.
- Evaporation: The slow process of vapour formation that occurs at the surface of a liquid.
- Evaporation can occur at temperatures below the boiling point.
Daily life example: Water spilled on a table gradually disappears due to evaporation.
7. Gaseous State
- Gases have no definite shape and no definite volume.
- They take the shape of their container and occupy all the available space.
- Their particles are far apart, with maximum interparticle spacing.
- Interparticle attractions are negligible.
- Particles move freely in all directions.
- Gases are highly compressible because of the large spaces between their particles.
Examples: Air, oxygen, methane and water vapour.
Remember: Gases spread throughout the available space because their particles move freely.
8. Interparticle Spacing
- Solids: Particles are closely packed, with minimum spacing.
- Liquids: Particles have slightly more spacing than in most solids.
- Gases: Particles are far apart, with maximum spacing.
Important exception: Ice has more interparticle spacing than liquid water.
9. Movement of Particles
- Particles of matter are always moving.
- In solids, particles vibrate about their fixed positions.
- In liquids, particles move within a limited space.
- In gases, particles move freely in all directions.
- Providing heat increases the movement of particles.
Example: Potassium permanganate spreads faster in hot water than in room-temperature or ice-cold water.
10. Diffusion
- Diffusion is the spreading and mixing of particles due to their constant motion.
- Diffusion occurs in liquids and gases.
- Gas particles mix easily because they move freely and have large interparticle spaces.
- Diffusion becomes faster when temperature increases.
Examples:
- The fragrance of perfume spreads throughout a room.
- Potassium permanganate spreads through water and gives it a uniform pink colour.
11. Effect of Thermal Energy
- Thermal energy affects the movement of particles and the physical state of matter.
- When matter is heated, its particles gain energy and move more vigorously.
- During melting, particles leave their fixed positions and begin moving around.
- During boiling, particles gain enough energy to escape into the gaseous state.
- Cooling reduces the movement of particles.
Change of state on heating: Solid → Liquid → Gas
12. Fluids
- Fluids are substances that can flow and do not retain a fixed shape.
- Both liquids and gases are classified as fluids.
- Liquids flow because their particles can move past one another.
- Gases flow and spread because their particles move freely in all directions.
13. Atoms and Molecules
- Atoms and molecules are the tiny particles that make up matter.
- Iron is made up of iron atoms, and gold is made up of gold atoms.
- Molecules are formed when atoms combine.
- A hydrogen molecule consists of two hydrogen atoms.
- A water molecule consists of two hydrogen atoms and one oxygen atom (H2O).
14. Acharya Kanad – Scientific Heritage
- Acharya Kanad was an ancient Indian philosopher.
- He proposed that matter is made up of tiny, indivisible and eternal particles called Parmanu.
- His ideas were written in the Vaisheshika Sutras.
15. Important Daily Life Applications
- Sugar in water: Sugar particles occupy spaces between water particles.
- Perfume: Fragrance spreads through the movement of air particles.
- Air in a syringe: Air can be compressed because gas particles have large spaces between them.
- Spilled milk: Milk flows and spreads because its particles can move past one another.
- Washing clothes: Soap particles interact with oil and water, helping remove oil from fabrics.
Quick Revision – Must Remember
- Matter is made up of extremely small constituent particles.
- Interparticle attractions hold particles together.
- Particles have spaces between them and remain in constant motion.
- Solid: Fixed shape and fixed volume.
- Liquid: No fixed shape, but fixed volume.
- Gas: No fixed shape and no fixed volume.
- Interparticle spacing: Solid < Liquid < Gas (generally).
- Attractive forces: Solid > Liquid > Gas.
- Particle movement increases when heat is supplied.
- Melting: Solid → Liquid.
- Boiling: Liquid → Gas.
- Evaporation: Slow vapour formation at the liquid surface.
- Diffusion: Spreading and mixing of particles.
- Fluids: Liquids and gases.
Examination Strategy
Exam Tips
Exam Tips – Particulate Nature of Matter
- Learn the definitions of constituent particles, interparticle spaces, interparticle attractions, diffusion, thermal energy, and fluids.
- Remember the properties of solids, liquids and gases, especially their shape, volume, particle spacing, movement and attractive forces.
- Prepare the comparison table of the three states of matter. It is useful for short-answer and difference-based questions.
- Understand how heating changes a solid into a liquid and a liquid into vapour. Remember the terms melting point and boiling point.
- Do not confuse boiling with evaporation. Boiling occurs throughout the liquid, while evaporation occurs at its surface.
- Revise the examples of diffusion, such as perfume spreading in a room and potassium permanganate spreading in water.
- Practise explaining why gases are compressible, liquids flow, and solids retain their shape using particle arrangement and attractive forces.
- Remember the exception: ice has more interparticle spacing than liquid water.
- Learn the melting points given in the chapter: ice (0 °C), urea (133 °C) and iron (1538 °C).
- Revise Acharya Kanad, the concept of Parmanu and the Vaisheshika Sutras.
Quick Revision Table
| Topic |
Key Point |
| Solid |
Fixed shape and volume; particles vibrate about fixed positions. |
| Liquid |
Fixed volume, no fixed shape; particles move within a limited space. |
| Gas |
No fixed shape or volume; particles move freely in all directions. |
| Melting |
Solid changes into liquid on heating. |
| Boiling |
Liquid changes into vapour throughout the liquid. |
| Evaporation |
Slow vapour formation at the liquid surface. |
| Diffusion |
Spreading and mixing of particles due to their constant motion. |
Answer-Writing Tips
- For questions asking “Why?”, explain using particle spacing, movement or attractive forces.
- For comparison questions, use a table instead of writing a long paragraph.
- Draw neat particle diagrams when asked to represent solids, liquids or gases.
- Use scientific terms correctly and support explanations with everyday examples.
- Read the question carefully and answer only what is asked.
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