NCERT Class 9 Science Chapter 1 Notes - Matter In Our Surroundings PDF Notes

Everything around us is made up of matter. This includes the air we breathe, the water we drink, and all of the products we use on a daily basis. Matter is anything that has weight and occupies space. This chapter, "Matter in Our Surroundings," will teach us about matter, its numerous forms, and how it evolves in different contexts. Understanding matter is very important because it is the base of everything we see and use in the world. This topic is detailed in the NCERT Notes for Class 9 and fits into the CBSE syllabus, which helps students understand Chemistry better.

The matter we see around us generally comes in three forms: solid, liquid, and gas. Take water as an example—it’s ice when it’s cold, water when it's warm, and steam when you heat it up. Matter can switch between these forms, which is important in nature and in everyday life. Think about melting ice caps because of climate change or how fridges and air conditioners work. In this chapter, students will learn about the different properties of matter, how it acts in different situations, and why all of this matters in real life.

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NCERT Class 9 Chapter 1 Class Notes

Topics of Class 9 of Science Matter in our Surroundings

Matter in Our Surroundings

Definition of Matter: Anything that occupies space and has mass is referred to as matter.

• Early Greek philosophers classified matter in the form of 5 elements: "panch tattva" - air, earth, fire, sky and water.
• Modern scientists classify matter in two ways: physically and chemically.
• Everything around us, be it living forms like plants or animals or non-living forms like tables, chairs, pencils, etc., is made of some material that is referred to by scientists as matter.

Let's discuss its classification on the basis of physical properties.

Physical Nature of Matter

Matter is Made Up of Particles

• When the question came about the nature of matter, there were two thoughts.
• The first said that matter is continuous, and the second said that matter is made up of small particles.
• At last, the second thought was proved right with the help of various experiments for example.

How small are these particles?

• If we add potassium permanganate to a solution, then its very small amount can change the colour of the whole solution, proving that it is made up of very small particles.
• Also, if we add Dettol to water, it will give the same smell after repeated dilution. This small experiment also supports the very small size of these particles.

Characteristics of Particles of Matter

Particles of matter have spaces between them

• It can be seen that one kind of matter is able to get dissolved in another kind of water, e.g., salt in water, lemonade, etc which proves that in reality, particles of one matter get into the spaces of the other.

Particles of matter are continuously moving

• Particles of matter are proven by experiments to be continuously moving and thus they possess kinetic energy.
• As the temperature rises, their kinetic energy also rises, and these particles start moving faster.
• The process where a particle of one kind of matter goes into spaces between another kind of matter is known as diffusion.
• It is observed that when heated, this process becomes faster.

Particles of matter attract each other

It has been observed that force of attraction is present between particles of matter and the strength of this force of attraction depends upon the kind of matter.

States of Matter

Matter exists in three different states, viz Solid, liquid and gas.

These different states of matter exist due to variations in their characteristics and properties discussed above.

The Solid State

Following are the characteristic features of solids :

• They possess a definite size (Volume) and a definite shape

• The shape of solid can be changed but it usually requires considerable force

• They are generally hard and rigid

• They have negligible compressibility

• Eg. Iron, silver, common salt etc.

The Liquid State

Following are the characteristic features of Liquid :

• They possess a definite volume but no definite shape

• It takes up the shape of the container in which it is placed

• They also have a tendency to flow.

• They are fluid and have very high diffusion capacity

• Particles move freely and are having greater spaces between them

• For Eg. Water, alcohol, milk, oil etc.

The Gaseous State

Following are the characteristic features of Gases :

• They neither possess a definite volume nor definite shape.

• They are having very high compressibility

• Particles of gases are having the highest diffusion rate.

• Particles move randomly and very fast.

• For Eg. air, Carbon dioxide, oxygen, hydrogen etc.

Can Matter Change its State?

We can take the example of water, as we know that it exists in all 3 states i.e.

• Solid as ice

• Liquid as its familiar water state

• Gas as vapour

Now we need to look into reasons those are responsible for bringing out these changes in the state of matter.

Effect of Change of Temperature

• When the temperature is increased, particles of the solid are seen with more kinetic energy.
• The particles start vibrating more, and the heat energy that is provided helps overcome the strong forces of attraction that are present between the particles.
• In this process, a particular stage is reached when the solid is melted into a liquid.
• The temperature at which a solid is converted into a liquid at atmospheric pressure is known as the melting point.
• The process of melting, which is the conversion of a solid state into a liquid state, is also known as fusion.
• We can see that after the ice is completely converted into a liquid, which is done by using the heat energy to overcome the force of attraction that is present between particles, there is no increase in the temperature of the ice.
• It is believed that the heat gets hidden in the beaker and is known as latent heat.
• The amount of heat energy that is required to convert one kilogram of solid into one kilogram of liquid at its melting point at atmospheric pressure is known as latent heat of fusion.
• In a similar way, when we provide heat to liquid water, its molecules get heated up and are able to overcome the force of attraction.
• Liquid starts changing into vapour.
• The temperature at which the liquid is converted into its vapour form at one atmospheric pressure is known as its boiling point.
• It can be seen that on increasing temperatures, solids can be converted into liquids, which can further be converted into gases.
• There's also a process by which we can directly convert solids into gases without converting it into liquids, and the process is sublimation.

Effect of Change of Pressure

• The state of matter can also be changed by changing its pressure, as we know that the characteristic feature of matter is the space present between the particles.
• By increasing the pressure, space can be removed, and by compressing the gas, we can change its state.
• On decreasing pressure and increasing temperature, we can liquefy a gas
• A very common example of this process is carbon dioxide.
• Solid carbon dioxide can be directly converted into its gaseous form by decreasing its pressure to one atm and as it's converted from its solid state to a directly gaseous state without coming into its liquid state, that’s why it's also known as dry ice.

Evaporation

• A change in the state of matter can also take place without a change in temperature or pressure.
• The particles of matter are always in motion and have kinetic energy.
• In the case of liquids, the kinetic energy of the molecules at the surface is higher than that of those present inside.
• Surface molecules are able to break the force of attraction and are converted into their vapour form.
• This conversion of liquid into its gaseous state at a temperature below its boiling point is known as evaporation.

Factors Affecting Evaporation

Following are the factors which affect evaporation (e.g., drying of wet clothes)

1. Surface Area: As we know, evaporation is a surface phenomenon and with an increase in temperature, the rate of evaporation also increases

2. Temperature: With the increase in temperature, the particles are able to get more heat energy and thereby more kinetic energy, and they are able to escape into the atmosphere more easily.

3. Decrease in Humidity: It helps in increasing evaporation, as when humidity is higher than the number of water particles in the surrounding area, fewer water particles will be able to get into the area.

4. Increase in Wind Speed: This helps in increasing the evaporation as those water vapours are able to move away from the cloth with the help of the wind. Also, the surrounding air has a smaller number of water particles so that more water vapours can evapourate there

How Does Evaporation Cause Cooling?

• When the process of evaporation goes on then the particles of that liquid absorbs the energy from their surroundings in order to regain the energy that they lost during evaporation which makes the surrounding cooler.
• Thus it can be concluded that the process of evaporation results in cooling.
• We must prefer cotton clothes during the summer because, in summer, when we sweat, that sweat evaporates.
• The energy equal to the latent heat of vaporisation is absorbed from our body, resulting in cooling our body, as cotton helps in the absorption of water and its evaporation in a much easier way.
• That’s why we must prefer cotton clothes in the summer.
• The presence of water droplets is seen around a cold water glass, and that happens because water vapours that are present in the air lose energy upon getting in contact with a cold surface and are then converted into their liquid state.

Most Important Questions of Class 9 Chapter 1

Question 1:

In which of the following conditions, the disrtance between the molecules of hydrogen gas would increase?
(i) Increasing pressure on hydrogen contained in a closed container
(ii) Some hydrogen gas leaking out of the container
(iii) Increasing the volume of the container of hydrogen gas
(iv) Adding more hydrogen gas to the container without increasing the volume of the container
(a) (i) and (iii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)

Answer 1: C

Molecules of gas acquire the complete volume of container.
These molecules move randomly inside the container, therefore the average molecular separation can be calculated by assuming the given number of molecules in given volume.
It is easy to understand, that the average molecular separation will increase by either increasing the volume keeping number of molecules constant or by decreasing number of molecules keeping volume constant.
Increasing pressure will lead to increase in temperature of a gas in closed container. This will increase the kinetic energy of molecules. Therefore, it will not help in increasing distance between molecules.
Hence statement numbers (i) and (iii) are correct which will lead to correct answer as option C.

Question 2:

Which condition out of the following will increase the evaporation of water?
(a) Increase in temperature of water
(b) Decrease in temperature of water
(c) Less exposed surface area of water
(d) Adding common salt to water

Answer 2:A

In case of evaporation, some liquid molecules take energy from rest of the liquid molecules and get converted in vapour.
If we increase the temperature of any liquid, it would be easy for some molecules to take the energy from rest of the molecules. As at higher temperature, all of them have higher amount of energy which will help process of evaporation.
The process of evaporation will be supported by exposure of surface to the surrounding, hence higher surface area leads to higher evaporation.
When we add common salt in water, some part of this salt covers the surface area along with water molecules which will create obstacles in evaporation.
Hence the correct answer of this question is option A.

Approach To Solve Class 9 Science Chapter 1 Questions

1. Revise all the Basics of Matter

• Matter occupies space and has mass.

• States of Matter are :

  • Solid that have a fixed shape and volume (e.g., Ice).

  • Liquid have a fixed volume but no fixed shape (e.g., Water).

  • Gas has no fixed shape or volume (e.g., Oxygen).

2. Focus on Basic Key Concepts

A. Physical Nature of Matter

• Particle Theory:

  • Matter is made of tiny particles.

  • Particles have space between them (intermolecular space).

  • Particles are in constant motion (kinetic energy).

B. States of Matter & Their Properties

C. Changes of State

1. Melting: Solid → Liquid (Heat absorbed).

2. Freezing: Liquid → Solid (Heat released).

3. Evaporation: Liquid → Gas (at any temperature).

4. Boiling: Liquid → Gas (at boiling point).

5. Condensation: Gas → Liquid (Cooling).

6. Sublimation: Solid → Gas directly (e.g., Camphor, Dry Ice).

D. Factors Affecting Evaporation

• With increase in temperature, rate of evaporation increases.

• With increase in surface Area, rate of evaporation increases.

• With dercrease in Humidity, rate of evaporation increases.

• With increase in wind speed, rate of evaporation increases.

E. Latent Heat

• Latent Heat of Fusion is the heat required to melt 1 kg solid into liquid.

• Latent Heat of Vaporization is the heat required to boil 1 kg of liquid into gas.

4. Important Formulas & Units

• Density = Mass / Volume (Unit: kg/m³ or g/cm³).

• Kelvin to Celsius:

• $\mathrm{K}={ }^{\circ} \mathrm{C}+273$

5. Practice Diagrams

• Particle arrangement in solids, liquids, and gases.

• Temperature vs. Time graph during state changes.

6. Common Mistakes to Avoid

• Confusion in evaporation (surface phenomenon) and boiling (bulk phenomenon).

• Always remember that intermolecular spaces are larger in gases than in solids.

• Misusing the units (e.g., using °C instead of Kelvin in gas laws).

Significance of NCERT Class 9 Science Chapter 1 Notes

The Matter in Our Surroundings Class 9th notes will assist you in revising the chapter and gaining an understanding of the main concepts addressed. These Notes are also not complicated, and they thoroughly explain step-by-step approaches to guarantee that students understand the concepts of this chapter, which is part of the CBSE Science syllabus for class 9. The Matter in Our Surroundings class 9 notes pdf download can be utilised for offline preparation.

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