Students can rely on these Class 8 Science Notes Chapter 7 Particulate Nature of Matter Class 8 Notes for complete exam preparation.
Class 8 Science Chapter 7 Particulate Nature of Matter Notes
Class 8 Science Curiosity Chapter 7 Notes
Class 8 Science Chapter 7 Notes – Particulate Nature of Matter Notes Class 8
→ Matter It is composed of extremely small particles.
→ Solid State It is a state where particles are tightly packed with strong intermolecular forces, e.g., Iron nail, chalk, etc.
→ Liquid State It is the state where particles are loosely packed and can flow. e.g. Water, oil, etc.
→ Gaseous State It is the state where particles are far apart and move freely, e.g., Air, steam, etc.
→ Melting Point The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure.
→ Boiling Point The temperature at which a liquid boils and turns into vapour at atmospheric pressure.
→ Fluids The substances that have the ability to flow. Both liquids and gases flow and do not retain a fixed shape.
→ Suspended Particulate Matter (SPM) The tiny dust particles which are suspended in air and are made up of a very large number of constituent particles, i.e., atoms and molecules, e.g., Smoke.
→ What are constituent particles of matter?
→ Why can’t we see the constituent particles of matter with the naked eye?
→ When chalk is crushed into powder, it still shows the same properties. What does this indicate about the nature of matter?
→ Name the invisible forces that hold the particles of matter together.
→ State two factors on which the strength of interparticle attraction depends.
→ State the reason why solids have a definite shape and volume, whereas gases do not.
→ What happens to the particles of a solid when it is heated to it’s melting point?
→ Iron has a much higher melting point than wax. Identify the factor responsible for this difference.
→ Why do liquids take the shape of the container but not change their volume?
→ Liquids and gases are grouped as fluids. What common property justifies this classification.
→ Why can gases be compressed easily while solids and liquids cannot?
→ How do interparticle forces and spacing differ between solids and gases?
→ What effect does temperature have on the movement of particles in matter?
→ Why does potassium permanganate spread faster in hot water than in cold?
→ Why does soap help to remove oil stains from clothes based on particle behaviour?
→ How does the spreading of perfume in a room show that gas particles move freely?
Compostion of Matter
- Matter is made up of very tiny particles called constituent particles that are too small to be seen with the naked eye.
- A constituent particle is the basic unit that makes up a larger piece of a substance or material.
- Even when a substance is broken into smaller parts (like chalk into powder), each tiny particle retains the original properties.
- Matter is particulate in nature. This can be shown when substances like sugar dissolves in water, its particles spread evenly throughout the liquid.
States of Matter and Their Characteristics
- The constituent particles of matter are held together by invisible forces called interparticle attractions or forces of attraction between particles.
- The strength of interparticle attractions depends on two factors.
- The nature of the substance.
- The distance between the particles (closer particles = stronger attraction).
- The strength of these forces of attraction determine the physical state (solid, liquid or gas) of a substance.
Ancient Indian philosopher Acharya Kanad (600 BCE) first proposed that matter is made of indivisible particles called Parmanu (atom) in his text Vaisheshika Sutras.
Solid State
- Solids have a definite shape and volume because their constituent particles are tightly packed.
- Strong interparticle attractions hold the particles in fixed positions, preventing them from moving freely.
- The particles in solids can only vibrate or oscillate about their fixed positions.
- On heating, the particles gain energy and vibrate more vigorously.
- When the vibrations become strong enough to overcome the interparticle forces, the solid begins to melt into a liquid.
- Melting point is the minimum temperature at which a solid melts to become a liquid at the atmospheric pressure.
- In the liquid state, particles are generally farther apart than in the solid state (except in cases like ice, where the solid has a more open structure).
- Solids with weak interparticle attractions (like wax or ice) melt at lower temperatures, while solids with strong attractions (like iron) have higher melting points.
- Examples of melting points of some solids are as follows (i) Ice → 0°C (ii) Urea → 133°C (iii) Iron → 1538°C
Solids like ice are exceptions. Their particles are slightly farther apart than in liquid water, which is why ice floats on water.
Liquid State
- Liquids have no fixed shape and they take the shape of the container in which they are kept in.
- The particles in liquids are not fixed and they are free to move and slide past one another.
- Liquids have a fixed volume and when they are transferred to containers of different shapes, the amount of liquid will remain the same. If a container is not clean, a small amount of water may stick to the walls, causing a slight decrease in volume during transfer.
- Liquids allow movement through them. For example, you can move your finger through water without breaking it, unlike solids.
- The interparticle attractions in liquids are weaker than in solids, allowing temporary displacement of particles.
- Despite weaker attractions, the forces are still strong enough to keep the particles close together in a liquid state.
- On heating a liquid, the particles gain energy and move more vigorously, reducing the strength of interparticle attractions.
- Boiling point is the temperature at which a liquid boils and turns into vapour at atmospheric pressure and forming bubbles inside the liquid.
- Evaporation is the slow process of vapour formation that occurs at all temperatures but only from the surface of the liquid.
Gaseous State
- Gases do not have a fixed volume. They expand to fill the entire space available in any container.
- Gases also do not have a fixed shape. They take the shape of the container in which they are present.
- The interparticle attractions in gases are negligible, which allows particles to move independently.
- Gas particles move freely and rapidly in all directions.
- The weak interparticle forces in gases make them highly compressible compared to solids and liquids.
- Both gases and liquids can flow and do not retain a fixed shape thus they are collectively called fluids.
- Gases differ from solids by following properties
- Gases have no definite shape.
- Gases have no definite volume.
- Gases have extremely weak or negligible interparticle attractions.
Gas particles fill spaces evenly. This is why perfume sprayed in one corner of a room soon reaches everywhere.
Interparticle Spacing
The behaviour of matter in different states depends critically on two factors – the forces between particles and the spaces between them.
- In solids, strong interparticle forces and minimal spaces between particles result in rigid structures.
- Liquids have moderate interparticle forces and slightly larger spaces, allowing them to flow while maintaining volume.
- Gases feature negligible interparticle forces and maximum spaces between particles, leading to their expansive nature.
- The amount of space between particles also varies and these differences in interparticle spacing explain why we can compress gases but not solids or liquids.
The word “particle” has different meanings in different contexts. In air pollution, Suspended Particulate Matter (SPM) refers to visible dust particles in air, which are much larger than the extremely tiny particles that make up matter. Even dust particles are made up of atoms and molecules-the true constituent particles of matter.
Movement of Particles
- Particles are always in motion in all three states of matter-solid, liquid and gas.
- The speed and freedom of particle movement depends on their arrangement and energy.
- In solids, particles vibrate in fixed positions.
- In liquids, particles can slide past one another and enable flow.
- In gases, particles move freely at high speeds in all directions.
- Temperature directly affects the motion of particles. At higher temperatures, particles gain more energy and move faster.
- For example, potassium permanganate dissolves faster in hot water than in cold because particles of water move faster at higher temperatures.
States of Matter and their Particle Nature
To understand the states of matter, we must first know how its paticles behave.
• In each state-solid, liquid, or gas the particles differ in arrangement, movement, and attractive forces. These differences decide the state in which matter appears.
Applications of Particle Behaviour in Daily Life
The particulate nature of matter plays a crucial role in many everyday processes. For example,
- Air can fill a balloon because the gas particles are free to move and exert pressure.
- Sugar dissolves in water because its tiny particles fit into the spaces between water particles.
- Soap removes oil stains from clothes because its molecules interact with both water and oil and lift the oil from the fabric.
- The spreading of the fragrance of incense stick across a room also proves that gas particles move rapidly and mix with other gases.
