NCERT Science Notes - Class 9
Chapter 1 - Matter in our surroundings

Welcome to AJs Chalo Seekhen. This webpage is dedicated to Class 9 | Science | Chapter 1 - Matter in our surroundings. The chapter delves about matter, which has mass and occupies space. This chapter explains the three states of matter—solids, liquids, and gases—and their characteristics. It highlights how temperature and pressure affect these states and includes concepts like evaporation and condensation. Understanding the behavior and properties of particles of matter forms the basis of this chapter, providing students with essential knowledge about the physical world and preparing them for more advanced topics in chemistry and physics. This foundational chapter equips students with the tools to explore and understand matter deeply.

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NCERT Science Notes - Class 9
Chapter 1 - Matter in our surroundings

What is Matter?

• Matter: Everything in the universe that has mass* and occupies space (volume**).
  • Examples: Air, food, stones, clouds, stars, plants, animals, water, sand.

• Early Indian Philosophers:
  • Classified matter as made up of five basic elements, called the "Panch Tatva":
    1. Air
    2. Earth
    3. Fire
    4. Sky
    5. Water
  • Believed that everything (living or nonliving) was made of these five elements.
• Ancient Greek Philosophers:
  • Similar classification to the Indian system.

• Physical properties: Matter can be classified based on its observable characteristics (shape, size, texture, etc.).
• Chemical nature: Matter can also be classified based on its chemical composition and reactions. 

1.1 - Physical Nature of Matter

1. Definition of Matter:
   • Matter is anything that occupies space and has mass. Examples include air, food, water, stones, plants, and animals.
2. Two Schools of Thought: One believed that matter is continuous (like a block of wood). The other believed matter is made up of particles (like grains of sand).
3. Experiment to Understand the Nature of Matter:
   • Activity 1.1: Dissolve salt/sugar in water and observe that the water level does not change. This shows that the particles of salt/sugar spread throughout the water, proving that matter is made up of small particles, not continuous blocks.
     
     

   Activity 1.1: Understanding the Particulate Nature of Matter

   • Objective: To observe the behavior of salt/sugar when dissolved in water and understand the particulate nature of matter.
   • Materials:
     • 100 mL beaker
     • Water (half-filled beaker)
     • Salt or sugar
     • Glass rod (for stirring)
   • Procedure:
     1. Fill the beaker halfway with water and mark the water level.
     2. Add some salt or sugar and stir with a glass rod.
     3. Observe whether the level of water changes after the salt/sugar dissolves.
   • Observations:
     • After stirring, the salt/sugar appears to disappear in the water.
     • The water level does not increase, indicating no change in volume.
   • Explanation:
     • The salt or sugar has dissolved into the water, spreading evenly throughout. This demonstrates that matter is made of particles that occupy the space between water molecules. The level of water doesn't rise because the particles of salt/sugar fit into the gaps between the water molecules, supporting the particulate nature of matter.
   This activity illustrates how matter is made up of small, discrete particles, even though the material seems to disappear or dissolve completely.
4. Explanation:
   • The particles of salt/sugar occupy the spaces between the water molecules, which is why the level of water doesn't change after dissolving. This indicates the particulate nature of matter.

• Matter: Anything that has mass and volume.
• Particles: The small units that matter is made up of.

1.1.2 - How Small Are These Particles of Matter?

Activity 1.2: Observing the Smallness of Particles

• Objective: To demonstrate how small the particles of matter are by repeatedly diluting potassium permanganate or Dettol in water.
• Materials:
  • 2–3 crystals of potassium permanganate
  • 100 mL of water
  • Clear water (for dilution)
  • Measuring cylinder or dropper
• Procedure:
  1. Dissolve 2–3 crystals of potassium permanganate in 100 mL of water to create a solution.
  2. Take 10 mL of this solution and add it to 90 mL of clear water.
  3. Repeat the dilution by taking 10 mL of the new solution and adding it to another 90 mL of clear water.
  4. Continue diluting 5 to 8 times.
  5. Observe whether the water remains colored after each dilution.
• Observation:
  • Even after repeated dilution, the water remains colored, though the color becomes lighter with each dilution.
• Explanation:
  • Smallness of Particles: This experiment shows that just a few crystals of potassium permanganate can color a large volume of water, even after multiple dilutions. This means that the particles of potassium permanganate are extremely small and continue to spread out and divide themselves into even smaller particles as the solution is diluted.
  • Millions of Particles: Each crystal of potassium permanganate contains millions of tiny particles, which are so small that they can be divided and distributed throughout the water without completely disappearing.
  • Smell of Dettol: If Dettol is used in place of potassium permanganate, the smell can still be detected even after repeated dilution. This shows that the particles of Dettol are also very small and spread out into the surrounding water, even when heavily diluted.

Activity 1.4: Observing the Movement of Particles in Water

Objective: To observe how particles of different substances (ink and honey) move in water and spread over time, demonstrating the movement of particles in matter.

Materials:

• Two glasses or beakers filled with water
• A drop of blue or red ink
• A drop of honey

1. Take two beakers or glasses and fill them with water.
2. In the first beaker, slowly add a drop of blue or red ink along the side of the glass.
3. In the second beaker, add a drop of honey in the same way, along the side.
4. Leave the glasses undisturbed in a corner of the class or your house.
5. Observe what happens immediately after adding the ink and honey, and continue observing over the next few hours or days.

1. Immediately after adding the ink:
   • The ink starts to slowly spread from where it was added.
   • The particles of ink begin to diffuse into the water, making the water around the drop lightly colored.
2. Immediately after adding honey:
   • The honey, being denser, tends to sink to the bottom of the glass.
   • Unlike the ink, the honey spreads much more slowly.
3. Over time:
   • Ink: The ink will gradually spread evenly throughout the water. The speed of this diffusion depends on factors such as temperature and whether the water is stirred or left still.
   • Honey: The honey takes much longer to spread and dissolve into the water, but eventually, the particles will distribute themselves.

• Ink Particles: The faster spreading of ink shows that the particles of ink are continuously moving, and their movement is more rapid because they mix easily with water.
• Honey Particles: Honey spreads much more slowly because it is thicker (has a higher viscosity). However, it eventually dissolves and distributes, demonstrating that even in viscous substances, particles are in motion.

1.2 - Characteristics of Particles of Matter

1.2.1 - Particles of Matter Have Space Between Them

• Explanation:
  • From Activities 1.1 and 1.2, we learned that substances like sugar, salt, Dettol, and potassium permanganate mix evenly in water without increasing the volume of the water. This happens because the particles of these substances fit into the spaces between the water particles.
  • Similarly, when making tea, coffee, or lemonade (nimbu paani), the particles of sugar or other ingredients mix into the spaces between the particles of water. This demonstrates that particles of matter have space between them.

1.2.2 - Particles of Matter Are Continuously Moving

Activity 1.3: Observing the Movement of Particles Using an Incense Stick

• Objective: To observe how particles of matter move by detecting the smell of incense from a distance.
• Materials:
  • Incense stick (unlit and lit)
  • Matchstick/lighter
• Procedure:
  1. Place an unlit incense stick in a corner of the room and slowly move closer to it.
     • Observation: You need to be very close to smell it.
  2. Light the incense stick and observe whether you can smell the fragrance from a distance.
     • Observation: Once lit, the smell of the incense reaches you even if you are sitting far from it.
• Explanation:
  • Movement of Particles: The fragrance of the unlit incense stick doesn’t spread far because the particles are not moving actively. However, when the incense stick is lit, the heat causes the particles of fragrance to move rapidly in all directions, spreading throughout the air.
  • Brownian Motion: This activity demonstrates that particles of matter are continuously moving, even in solids, liquids, and gases. The particles of fragrance spread by colliding with air particles, allowing the smell to travel across the room.
• Conclusion:
  • Particles of Matter Are Always in Motion: The activity illustrates that the particles of matter, whether in gases, liquids, or solids, are always moving. When the particles gain energy (such as from heat), they move faster, as seen when the incense stick is lit.

Activity 1.5: Effect of Temperature on Diffusion

1.2.3 - PARTICLES OF MATTER ATTRACT EACH OTHER

Activity 1.6: Human Chain Game

Objective: To observe how particles of matter attract each other by comparing the strength of connections between human chains.

Materials:

• A group of students divided into four smaller groups.

1. Group 1: Students form a human chain by locking arms from behind, similar to Idu-Mishmi dancers.
2. Group 2: Students form a chain by holding hands.
3. Group 3: Students form a chain by touching each other only with their fingertips.
4. Group 4: The remaining students run around and try to break these human chains one by one.

• Which group was the easiest to break? Why?
  • Answer: The third group (fingertip chain) was the easiest to break because the connection between the particles (students) was the weakest.
• In which group did the particles hold each other with the maximum force?
  • Answer: The first group (locked arms) represented the strongest force of attraction between particles, as the students were holding each other tightly.

• This activity demonstrates that particles of matter attract each other with varying strength. The stronger the force between particles, the harder it is to break the connection. In the same way, different substances have different strengths of particle attraction.

Activity 1.8: Surface Tension of Water

Objective: To observe the attraction between particles of water at the surface.

Materials:

• Container with water

1. Take some water in a container.
2. Try cutting the surface of the water with your fingers.

• Were you able to cut the surface of water?
  • Answer: No, you cannot cut the surface of water.
• What could be the reason behind the surface of water remaining together?
  • Answer: The surface of water remains together because of the force of attraction between the water particles, which creates a phenomenon known as surface tension.

• The force of attraction between water molecules at the surface pulls them together, creating a tight surface layer. This is why it's difficult to break or cut the surface of water, demonstrating that particles of matter attract each other even in liquids.

1. Force of Attraction: The force that holds particles of matter together. It varies in strength depending on the type of substance.
2. Surface Tension: The force of attraction between particles on the surface of a liquid, causing the surface to behave like a stretched elastic sheet.
3. Kinetic Energy: The energy possessed by moving particles. While it is responsible for the movement of particles, the force of attraction keeps them connected.
4. Matter: Anything that occupies space and has mass. Matter is made up of particles that are attracted to each other.

1.3 - States of Matter

Matter exists in three states: solid, liquid, and gas. These states arise due to differences in the properties of the particles that make up matter. Let’s explore the solid state first.

1.3.1 - The Solid State

Objective: To study the properties of solids by examining common objects.

Materials:

• A pen
• A book
• A needle
• A wooden stick

1. Sketch the shape of the above objects by moving a pencil around them.
2. Analyze their shape, volume, and boundaries.
3. Apply force (hammering, pulling, or dropping) to these objects and observe the results.
4. Check whether these objects can be compressed or diffuse into each other.

• Do all these have a definite shape, distinct boundaries, and a fixed volume?
  • Answer: Yes, all these objects have a definite shape, distinct boundaries, and fixed volume.
• What happens if they are hammered, pulled, or dropped?
  • Answer: These objects may break under force, but it is difficult to change their shape. Solids resist changes in shape, showing rigidity.
• Are these capable of diffusing into each other?
  • Answer: No, solids cannot diffuse into each other. This shows that solids do not mix or spread out like liquids or gases.
• Can they be compressed by applying force?
  • Answer: No, these solids show negligible compressibility, meaning they cannot be compressed easily.

• Solids are rigid, meaning they maintain their shape when an external force is applied. They have definite shape, volume, and boundaries. Even when force is applied, they resist deformation, though they can break under sufficient force.

1.3.2 - The Liquid State

In the liquid state, matter exhibits different characteristics compared to solids. Liquids do not have a fixed shape but have a fixed volume. They flow easily and take the shape of the container they are placed in.

Activity 1.10: Exploring the Properties of Liquids

Objective: To observe how liquids behave when transferred between containers and spilled, and to understand their flow and shape properties.

Materials:

• Water, cooking oil, milk, juice, cold drink
• Containers of different shapes
• Measuring cylinder (50 mL mark)

1. Spilling Liquids:
   • Spill some of the liquids (e.g., water or milk) on the floor. What happens to their shape and flow?
   Observation: Liquids spread out and take on an irregular shape when spilled, showing that they do not have a definite shape.
2. Transferring Liquids:
   • Measure 50 mL of any liquid using the measuring cylinder and transfer it to different containers (e.g., a glass, bowl, or flask).
   Questions and Answers:
   • Does the volume remain the same in each container?
     • Answer: Yes, the volume remains the same (50 mL) in every container.
   • Does the shape of the liquid remain the same?
     • Answer: No, the shape of the liquid changes according to the shape of the container.
   • Does the liquid flow easily from one container to another?
     • Answer: Yes, the liquid flows easily, showing its fluidity.

• Liquids have a fixed volume but no fixed shape. They take the shape of the container they are poured into. Liquids are also fluid, meaning they can flow easily.

1. Liquids Have No Fixed Shape:
   • Liquids take the shape of the container they are placed in, but their volume remains constant.
2. Liquids Are Fluid:
   • Liquids flow and can be transferred from one container to another. This ability to flow makes them fluids, unlike solids which are rigid.
3. Liquids Can Diffuse:
   • Liquids can diffuse into other liquids, as shown in Activity 1.4 and 1.5. For example, when we mix water with juice, the two liquids spread evenly.
   • Gases can also diffuse into liquids, such as oxygen and carbon dioxide dissolving in water. This diffusion is crucial for aquatic animals and plants, which rely on dissolved oxygen to breathe.

• The rate of diffusion is faster in liquids compared to solids.
• This is because particles in a liquid move more freely and have more space between them than in solids, allowing them to intermix quickly.

1. Fluid: A substance that flows easily and can change shape. Both liquids and gases are fluids.
2. Diffusion: The movement of particles from an area of higher concentration to an area of lower concentration. In liquids, diffusion occurs more rapidly due to the movement of particles.

• Breathing in Aquatic Animals: Aquatic animals breathe using dissolved oxygen in water, which diffuses from the atmosphere into the liquid. Without this, survival in water would not be possible.
• Everyday Liquids: Liquids like water, oil, and juice all behave similarly, having fixed volume but adapting their shape based on the container they are in.

1.3.3 - The Gaseous State

Gases, unlike solids and liquids, exhibit unique properties such as high compressibility and rapid diffusion. These characteristics are due to the large spaces between gas particles and their fast, random movement.

Objective: To compare the compressibility of solids, liquids, and gases by observing their behavior in a syringe.

Materials:

• Three 100 mL syringes
• Rubber corks
• Water
• Chalk pieces
• Vaseline (for smooth piston movement)

1. Take three syringes and close their nozzles with rubber corks.
2. Remove the pistons from the syringes.
3. Leave one syringe empty, fill the second syringe with water, and fill the third syringe with pieces of chalk.
4. Insert the pistons back into the syringes, applying vaseline if needed for smoother movement.
5. Attempt to compress the contents by pushing the pistons in each syringe.

• Which syringe is the easiest to compress?
  • Answer: The syringe filled with air (empty syringe) is the easiest to compress, showing that gases are highly compressible.
• Why is it harder to compress the water or chalk?
  • Answer: Liquids and solids are less compressible due to the closer arrangement of particles in them.

• Gases are highly compressible, much more so than solids and liquids. This is due to the large spaces between gas particles, which allow them to be squeezed closer together. Solids and liquids, on the other hand, have little space between particles, making them difficult to compress.

1. High Compressibility:
   • Gases are easily compressible, meaning large volumes of gas can be compressed into smaller containers. This is why compressed gases like LPG (liquefied petroleum gas) for cooking and CNG (compressed natural gas) for vehicles are easily stored in cylinders.
2. Fast Diffusion:
   • Gases diffuse very quickly compared to solids and liquids. For example, the smell of food can reach you quickly from the kitchen due to the rapid diffusion of gas particles.
   • The particles of gas mix with air, allowing the aroma of food to travel to your nose. This is possible because gas particles move freely and rapidly.
3. Random Movement:
   • Gas particles are in constant random motion, moving at high speeds. This movement causes gas particles to collide with one another and with the walls of the container.
4. Pressure in Gases:
   • The pressure exerted by a gas is due to the force gas particles apply when they collide with the walls of the container. The more frequent the collisions, the higher the pressure.

1. Compressibility: The ability of a substance to be compressed or reduced in volume by applying pressure. Gases are highly compressible compared to solids and liquids.
2. Diffusion: The movement of particles from an area of higher concentration to an area of lower concentration. Gases diffuse much faster than solids and liquids due to the larger spaces between their particles and their high kinetic energy.
3. Pressure: The force per unit area exerted by gas particles as they collide with the walls of their container.

• LPG and CNG: These gases are used in compressed form because large amounts of gas can be stored in small containers, making transportation and usage more convenient.
• Oxygen Cylinders: In hospitals, oxygen is stored in cylinders in compressed form to supply a large amount of gas to patients.

• The rate of diffusion in gases is much faster than in solids or liquids because gas particles move at high speeds and have more space to spread out. This is why we can smell food or perfumes quickly even from a distance.

1.4 - Can Matter Change its State?

1.4.1 - Effect of Change of Temperature

Activity - 1.12

Objective: To observe the effect of temperature on the change of state from solid to liquid and liquid to gas.

• 150 g of ice
• Beaker
• Laboratory thermometer
• Low flame heat source
• Glass rod (for stirring)

1. Set up: Take about 150 g of ice in a beaker and suspend a laboratory thermometer such that its bulb touches the ice (Fig. 1.6).
2. Melting (Solid to Liquid):
   • Start heating the beaker on a low flame.
   • Observe and record the temperature when the ice begins to melt.
   • Continue heating and record the temperature when all the ice has converted into water.
3. Boiling (Liquid to Gas):
   • Insert a glass rod into the beaker for stirring.
   • Continue heating the water while stirring it until the water starts boiling.
   • Keep observing the thermometer and note the temperature when the water reaches its boiling point and most of the water vaporizes.

1. When Ice Starts Melting:
   • The temperature at which ice starts melting is 0°C. This is the melting point of ice, where solid ice begins to change into liquid water.
2. When Ice is Fully Converted to Water:
   • During the melting process, the temperature remains constant at 0°C until all the ice has melted into water. This indicates that the heat energy is used to break the bonds between the particles of ice without raising the temperature.
3. When Water Starts Boiling:
   • The temperature at which water starts boiling is 100°C. This is the boiling point of water, where liquid water starts to convert into water vapor (gas).
   • As the water continues to boil, the temperature stays constant at 100°C even though heat is still being applied. This is because the energy is being used for the process of vaporization.

• Effect of Temperature on State Change:
  • When we heat a substance, the particles of matter absorb energy. This energy increases their kinetic energy and causes them to move faster.
  • In the case of ice (solid), the heat energy weakens the intermolecular forces, allowing the solid to change into a liquid (water).
  • Once the ice has completely melted, the liquid water absorbs more heat. At 100°C, the water particles have enough energy to overcome the forces keeping them in the liquid state, and they escape into the air as water vapor (gas).

1. Melting Point: The temperature at which a solid changes into a liquid (for ice, it's 0°C).
2. Boiling Point: The temperature at which a liquid changes into a gas (for water, it's 100°C).
3. Latent Heat: The energy absorbed or released during a change of state without changing the temperature of the substance.
   • Latent Heat of Fusion: The heat required to convert a solid into a liquid without changing its temperature.
   • Latent Heat of Vaporization: The heat required to convert a liquid into a gas without changing its temperature.

• Change of state occurs when a substance absorbs or loses heat, but the temperature remains constant during the process. This is because the absorbed heat is used to break the intermolecular forces, rather than raising the temperature of the substance.

Activity 1.13: Sublimation Experiment

1.4.2 - Effect of Change of Pressure

The state of matter can be changed not only by changing the temperature but also by applying pressure. The main difference between different states of matter (solid, liquid, and gas) lies in the distance between particles. When pressure is applied to a gas, it compresses, and the particles come closer.

What happens when we compress a gas?

When pressure is applied to a gas enclosed in a cylinder, the particles of gas come closer to each other. If we increase the pressure and reduce the temperature sufficiently, the gas can liquefy, changing from the gaseous state to the liquid state.

Example of Solid Carbon Dioxide (Dry Ice):

• Solid carbon dioxide (CO₂) is stored under high pressure.
• When the pressure is reduced to 1 atmosphere, solid CO₂ converts directly into gas without going through the liquid state. This is why solid carbon dioxide is also called dry ice.

1. Dry Ice: Solid carbon dioxide that sublimates (changes directly from a solid to a gas) at normal atmospheric pressure without passing through the liquid state.
2. Liquefaction of Gases: The process of converting gases into liquids by applying pressure and reducing temperature.

• Pressure and temperature together play an important role in determining the state of a substance (solid, liquid, or gas).
• By increasing pressure and lowering the temperature, we can compress gases and even liquefy them.

1.5 - Evaporation

1.5.1 - Factors Affecting Evaporation

1.5.2 - How Does Evaporation Cause Cooling?

NCERT Science Notes - Class 9 Chapter 1 - Matter in our surroundings

NCERT Science Notes - Class 9 Chapter 1 - Matter in our surroundings