Complete Solutions and Summary of Particulate Nature of Matter – NCERT Class 8, Science, Chapter 7 – Summary, Questions, Answers, Extra Questions
Detailed summary and explanation of Chapter 7 ‘Particulate Nature of Matter’ with all question answers, extra questions, and solutions from NCERT Class VIII, Science.
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Particulate Nature of Matter
Chapter 7: Curiosity — Textbook of Science for Grade 8
Complete Study Guide with Interactive Learning
Chapter Overview
What You'll Learn
Composition of Matter
Understanding that matter is made of tiny particles and exploring through activities like breaking chalk and dissolving sugar.
States of Matter
Exploring solids, liquids, and gases based on interparticle attractions and spacing.
Interparticle Spacing
Learning how spacing differs in states and affects properties like compressibility.
Particle Movement
Observing how particles move in different states through experiments with potassium permanganate and incense.
Historical Context
This chapter explores the particulate nature of matter, drawing from ancient Indian philosopher Acharya Kanad's idea of 'Parmanu' (atom) as indivisible particles. It uses activities to demonstrate that matter consists of tiny particles held by attractions, explaining states like solid, liquid, and gas.
Key Highlights
Matter is composed of particles with interparticle spaces and attractions. Solids have strong attractions and minimal spacing, liquids have weaker ones, and gases have negligible attractions with maximum spacing. Activities illustrate melting, boiling, dissolution, and diffusion.
Comprehensive Chapter Summary
1. Introduction and Probing Questions
The chapter opens with an illustration of children on a riverbank collecting pebbles and pondering questions like why stones or sand can be piled but not water, why water takes the shape of folded hands but loses it when released, how invisible air adds weight to balloons, and if today's air is the same as thousands of years ago. It encourages sharing questions. The text explains that pebbles, stones, and sand come from eroded rocks in mountains, carried by rivers and broken further into finer grains. It questions if these grains are the smallest units or can be broken down more.
2. What Is Matter Composed of?
Activity 7.1: Let us explore - Breaking Chalk
Take a stick of chalk (Fig. 7.1a) and break it into two pieces (Fig. 7.1b). Continue breaking until difficult by hand. Grind small pieces with mortar and pestle (Fig. 7.1c). Observe fine powder with magnifying glass (Fig. 7.1d). Each grain is still chalk. Grinding is a physical change; substance remains the same, only size reduces. Imagining further grinding reaches stage where particles can't be broken - these are constituent particles, basic building blocks.
Activity 7.2: Let us perform - Dissolving Sugar
Fill glass tumbler with water. Add two teaspoons sugar. Taste top layer without stirring - not sweet. Stir until dissolved (Fig. 7.2). Taste top layer - sweet. Sugar present but invisible, detected by taste. Sugar breaks into constituent particles occupying interparticle spaces in water. Particles too small to see.
Key Idea and Heritage
Activities show matter composed of extremely small particles, not visible even under ordinary microscope. Chalk and sugar break into constituent particles. Interparticle spaces exist, as sugar particles fit between water particles. But how are particles held to form solids? Our scientific heritage: Acharya Kanad proposed Parmanu as tiny, indivisible eternal particles in Vaisheshika Sutras.
3. What Decides Different States of Matter?
Constituent particles held by attractive interparticle forces. Strength depends on nature and distance; increases with closeness. Strength decides physical state.
7.2.1 Solid State
Activity 7.3: Collect solids like iron nail, rock salt, stone, wood, key, aluminium (Fig. 7.3). Observe shapes, sizes; hammer them. All have definite shape, volume due to tightly packed particles, strong attractions, fixed positions (vibrate only). Heating increases vibrations (Fig. 7.4); at melting point, particles leave positions, become liquid. Melting point: minimum temperature solid melts to liquid at atmospheric pressure. Examples: Ice 0°C, Urea 133°C, Iron 1538°C (Table 7.1).
7.2.2 Liquid State
Activity 7.4: Three containers A, B, C marked 200 mL (Fig. 7.5). Fill A with water; transfer to B, then C. Water takes container shape, volume constant. Liquids no fixed shape, fixed volume; particles move freely in limited space. Attractions weaker than solids; finger through water displaces temporarily (Fig. 7.6). Heating to boiling point: vigorous movement, particles escape to vapour. Boiling point: temperature liquid boils to vapour. Evaporation: slower surface process below boiling point.
7.2.3 Gaseous State
Activity 7.5: Two gas jars A, B. Collect smoke in A (Fig. 7.7a,b); place B over, remove plate (Fig. 7.7c). Smoke fills B (Fig. 7.7d). Gases no fixed volume/shape, fill space. Particles free, negligible attractions. Can use iodine vapour (Fig. 7.8). Liquids/gases flow, called fluids.
4. How Does the Interparticle Spacing Differ in the Three States of Matter?
Activity 7.6: Let us experiment - Syringe Compression
Syringe without needle, plunger out (Fig. 7.9a). Thumb over end (b), push in (c). Air volume decreases - compressible, large spaces. Water incompressible. Gases maximum spacing, solids minimum, liquids intermediate.
Activity 7.7: Let us observe - Dissolving Solids
Half-fill vessel with water, mark A (Fig. 7.10a). Add sugar, mark B (b). Stir (c), mark C (d). Level decreases after dissolution - sugar particles occupy water spaces (Fig. 7.11). Repeat with salt/glucose (dissolve), sand/stone (don't, volume increases). Sand insoluble, settles.
Key Idea
Solids closely packed, some space (Fig. 7.12a); liquids more (b); gases maximum (c). SPM: dust particles larger than constituent particles, made of many atoms/molecules.
5. How Particles Move in Different States of Matter?
Activity 7.8: Let us experiment - Potassium Permanganate Diffusion
Water tumbler, add potassium permanganate. Streaks spread (Fig. 7.13a), uniform pink (b). Water particles in motion pull and spread solute. Insolubles like sand don't. Think like scientist: Hot, room, ice-cold water - spreads fastest in hot due to faster movement.
Activity 7.9: Let us find out - Incense Diffusion
Light incense in room corner (Fig. 7.14). Fragrance spreads. Air particles hit fragrance particles, diffusing. Examples: perfume, cooking smells.
Ever Heard Of... Soap Cleaning
Soap particles surround oil on clothes; one end attaches to oil, other to water, lifting oil (Fig. 7.15).
6. Wrap Up!
Matter made of particles held by attractions, strength depending on distance/thermal energy. Solids: low energy, close particles, strong forces. Melting: overcomes forces for liquid. Gases: high energy, free movement. Table summarizes states.
Key Concepts and Definitions
Constituent Particles
Basic building blocks of matter that cannot be broken further.
Interparticle Spaces
Spaces between particles; maximum in gases, minimal in solids.
Interparticle Attractions
Forces holding particles together; strongest in solids, negligible in gases.
Melting Point
Temperature where solid becomes liquid at atmospheric pressure.
Boiling Point
Temperature where liquid becomes gas with bubble formation.
Evaporation
Slow vapor formation at surface below boiling point.
Important Facts and Figures
Questions and Answers from Chapter
Short Questions
Q1. The primary difference between solids and liquids is that the constituent particles are?
Q2. Melting ice into water is an example of the transformation of a solid into a liquid. True or False?
Q3. Melting process involves a decrease in interparticle attractions during the transformation. True or False?
Q4. Solids have a fixed shape and a fixed volume. True or False?
Q5. The interparticle interactions in solids are very strong, and the interparticle spaces are very small. True or False?
Q6. When we heat camphor in one corner of a room, the fragrance reaches all corners of the room. True or False?
Q7. On heating, we are adding energy to the camphor, and the energy is released as a smell. True or False?
Q8. If we could remove all the constituent particles from a chair, what would happen?
Q9. Why do gases mix easily, while solids do not?
Q10. When spilled on the table, milk in a glass tumbler flows and spreads out, but the glass tumbler stays in the same shape. Why?
Q11. Why does the water in the ocean taste salty, even though the salt is not visible?
Q12. Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids?
Q13. What is the melting point of ice?
Q14. What are interparticle spaces?
Q15. What holds particles together?
Medium Questions
Q1. The primary difference between solids and liquids is that the constituent particles are?
Q2. Melting ice into water is an example of the transformation of a solid into a liquid. True or False? Correct if false.
Q3. Melting process involves a decrease in interparticle attractions during the transformation. True or False? Correct if false.
Q4. Solids have a fixed shape and a fixed volume. True or False? Correct if false.
Q5. The interparticle interactions in solids are very strong, and the interparticle spaces are very small. True or False? Correct if false.
Q6. When we heat camphor in one corner of a room, the fragrance reaches all corners of the room. True or False? Correct if false.
Q7. On heating, we are adding energy to the camphor, and the energy is released as a smell. True or False? Correct if false.
Q8. If we could remove all the constituent particles from a chair, what would happen?
Q9. Why do gases mix easily, while solids do not?
Q10. When spilled on the table, milk in a glass tumbler flows and spreads out, but the glass tumbler stays in the same shape. Justify.
Q11. Why does the water in the ocean taste salty, even though the salt is not visible? Explain.
Q12. Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids? Explain.
Q13. What happens when sugar dissolves in water?
Q14. Why can't solids be compressed easily?
Q15. How do particles behave in gases?
Long Questions
Q1. The primary difference between solids and liquids is that the constituent particles are?
Q2. Which of the following statements are true? Correct the false statements.
Q3. Choose the correct answer with justification. If we could remove all the constituent particles from a chair, what would happen?
Q4. Why do gases mix easily, while solids do not?
Q5. When spilled on the table, milk in a glass tumbler flows and spreads out, but the glass tumbler stays in the same shape. Justify this statement.
Q6. Represent diagrammatically the changes in the arrangement of particles as ice melts and transforms into water vapour.
Q7. Draw a picture representing particles present in the following: (i) Aluminium foil (ii) Glycerin (iii) Methane gas
Q8. Observe Fig. 7.16a which shows the image of a candle that was just extinguished after burning for some time. Identify the different states of wax in the figure and match them with Fig. 7.16b showing the arrangement of particles.
Q9. Why does the water in the ocean taste salty, even though the salt is not visible? Explain.
Q10. Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids? Explain.
Q11. Explain why sugar dissolves in water but sand does not.
Q12. Describe the movement of particles in liquids using an activity.
Q13. How does interparticle spacing differ in gases from solids and liquids?
Q14. What happens to particles during melting and boiling?
Q15. Explain Acharya Kanad's contribution to the idea of matter.
Interactive Knowledge Quiz
Test your understanding of Particulate Nature of Matter
Quick Revision Notes
Solid State
- Fixed shape/volume
- Strong attractions
- Minimal spacing
Liquid State
- No fixed shape
- Fixed volume
- Weaker attractions
Gaseous State
- No fixed shape/volume
- Negligible attractions
- Maximum spacing
Particle Movement
- Solids: Vibrate
- Liquids: Slide
- Gases: Free
Exam Strategy Tips
- Draw diagrams
- Explain activities
- Compare states
- Use tables
- Recall melting points
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