Matter

This chapter usually breaks down a few key ideas about this “matter”:

First off, it helps you understand just what counts as matter. It’s not your feelings or a beam of light, for example. It’s the things you can touch and see (most of the time!).

Then, it talks about the basic characteristics of matter:

• It has mass, which is just how much “stuff” is in something.
• It takes up space, which we call its volume.

Next up, you’ll dive into the three main ways matter can exist – what we call the states of matter:

• Think of a solid, like a rock or a table. It has its own shape and doesn’t change its volume easily. The tiny bits that make it up are packed super close together.
• Then there’s a liquid, like water or juice. It can flow and take the shape of whatever container you pour it into, but it still has a definite amount (volume). The little bits inside are closer than in a gas but can still move around.
• Finally, there’s a gas, like the air around you or steam. It doesn’t have its own shape or volume; it just spreads out to fill whatever space it’s in. The tiny bits are really far apart and zipping around like crazy.

The chapter might also give you a sneak peek into what matter is made of at a really tiny level – things called molecules and even smaller things called atoms. How these tiny bits are arranged and how much they move around is what makes something a solid, a liquid, or a gas.

You might also learn a bit about the spaces between these tiny bits (intermolecular space) and the forces that pull them towards each other (intermolecular forces). These things play a big role in why solids are rigid and gases are… well, gassy!

Finally, the chapter often touches on how you can change matter from one state to another by heating things up or cooling them down. Think about ice turning into water when it gets warmer, or water turning into steam when it boils.

Activity – 2

Classify 20 objects around you as solids, liquids and gases

Solids:

book, table,chair, pen/pencil, mobile, phone, door, wall, shoe, key, coin

Liquids:

Water,Milk,Cooking ,oil,Juice,Ink

Gases:

Air,Steam,The gas in a balloon,The exhaust fumes from a vehicle (when visible),The helium in a party balloon.

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) The molecules of each substance are identical.
Ans: False

(b) The intermolecular forces are effective at all distances between the two molecules.
Ans: False

(c) The molecules in a substance arc in random motion.
Ans: Tme

(d) In a gas, the molecules can move anywhere in space. .
Ans: Tme

(e) The liquids are less viscous than the gases.
Ans: False

2. Fill in the blanks

(a) All the molecules of a substance are——–

Ans : Identical.
(b) The intermolecular spacing is ———in solids —–in liquids and—— in gases.

Ans : least ,more, still more
(c) The molecular motion in liquid and gas is in a ——-path.

Ans : Zig-zag
(d) In a solid, the molecules ——–but they remain at their fixed positions.

Ans : Vibrate to and fro 

(e) The intermolecular forces are the weakest in.

Ans : Gases
(f) A solid exerts pressure.

Ans : Downwards on its base
(g) The gases are ——-dense.

Ans : Least

(h) A solid is the ———rigid.

Ans : Most

3. Select the correct alternative

(a) The diameter of a molecule is approximately

1.  1 cm
2.  10 cm
3.  10-10 m
4.  1 m

Ans:10-10 m

(b) The intermolecular forces are strongest in

1.  solids
2.  liquids
3.  gases
4.  both (i) and (ii)

Ans: solids

(c) The molecules

1.  in solid, liquid and gas, move freely anywhere.
2.  in a solid, move freely within its boundary.
3.  in a liquid, move within its boundary.
4.  in a gas, move only within its boundary.

Ans: in a liquid, move within its boundary.

d) The solids are

1.  more dense
2.  less dense
3.  least dense
4.  highly compressible

Ans: more dense

(e) The intermolecular forces in liquids are

1.  as strong as in solids
2.  stronger than in solids
3.  weaker than in solids
4.  weaker than in gases

Ans: weaker than in solids

4. Match the following columns

Ans:

Matter is anything around us that has mass and takes up space (has volume). You can think of it as the “stuff” that everything is made of. For example, a book, water, air, and even you are made of matter.  

Composition of Matter:

Matter is made up of very tiny particles. These tiny particles are so small that we cannot see them with our eyes. These particles are called molecules.  

• Molecules: Molecules are the smallest units of a substance that still show all the properties of that substance. Imagine breaking a drop of water into smaller and smaller pieces. Eventually, you would reach a tiny particle that is still water. That tiny particle is a molecule of water.  

Molecules themselves are made up of even smaller particles called atoms.  

• Atoms: Atoms are the basic building blocks of all matter. Different types of atoms join together to form different types of molecules. For example, a water molecule is made up of two hydrogen atoms and one oxygen atom joined together.

7)Describe a simple experiment to illustrate the existence of intermolecular spacing.

Ans:

Take a measuring cylinder and pour, say, 50 milliliters of water into it. Mark the water level clearly. Now, slowly add a spoonful of salt to the water and stir it well until all the salt dissolves.

You’ll observe that even after the salt has completely disappeared into the water, the new total volume of the salt and water mixture is only slightly more than the initial 50 milliliters of water. It’s definitely not 50 ml (water) + the volume of the salt you added.

This happens because the tiny particles of salt don’t just sit on top of the water particles. Instead, they actually fit into the spaces that exist between the water particles.  This “fitting in” without a significant increase in volume demonstrates that there are gaps, or intermolecular spaces, between the molecules of water.  The salt particles are small enough to occupy these spaces. 

8)What do you mean by intermolecular forces ?

Ans:

Imagine tiny magnets between the molecules of a substance. Intermolecular forces are like those magnets – they’re the attractions that hold nearby molecules together. These forces can be strong or weak, and their strength is a big reason why some things are solid, some are liquid, and some are gas. Stronger forces mean molecules are held tightly, while weaker forces let them move around more freely

9)What are the forces of cohesion and adhesion ?

Ans:

Force of cohesion is like the “stick-together” power between molecules of the same substance. Think of water forming droplets – the water molecules are attracted to each other.  

Force of adhesion is the “sticking” power between molecules of different substances. 

10)State three characteristics of molecules of matter.

Ans:

1. Molecules are extremely tiny: They are far too small to be seen with the naked eye.
2. Molecules have spaces between them: These gaps are known as intermolecular spaces.
3. Molecules attract each other: This attraction is called intermolecular force.

11)State the approximate spacing between two molecules of a matter.

Ans:

The approximate spacing between two molecules in matter varies greatly depending on the state:

• In solids, the spacing is extremely small, almost touching.  

• In liquids, the spacing is a little larger, allowing them to slide past each other.
• In gases, the spacing is very large compared to the size of the molecules themselves.

12)How do the solids, liquids and gases differ in their following properties

(a) Size

(b) Shape

(c) Density

Answer:

13)The molecules in a substance are in motion. What type of path do they follow ?

Ans:

The molecules in a substance are constantly jiggling and moving in a random, zigzag path.  It’s not a straight line because they keep bumping into each other. This chaotic movement is often called Brownian motion.  

14)Describe a simple experiment to illustrate that molecules are not at rest, but they constantly move.

Ans:

This happens because the tiny particles of potassium permanganate are constantly moving and bumping into the water molecules, gradually spreading out and coloring the entire solution. If the molecules weren’t moving, the purple color would just stay concentrated at the bottom.

15)Write down five general properties of solids, liquids and gases.

Ans:

Solids:

1. Fixed shape
   
2. Fixed volume
   
3. Cannot be compressed
   
4. Particles are tightly packed
   
5. Do not flow
   

Liquids:

1. No fixed shape (takes shape of container)
   
2. Fixed volume
   
3. Slightly compressible
   
4. Particles are loosely packed
   
5. Can flow
   

Gases:

1. No fixed shape
   
2. No fixed volume
   
3. Highly compressible
   
4. Particles are far apart
   
5. Flows easily in all directions

16)Give the molecular model for a solid and use it to explain why a solid has a definite volume and a definite shape.

Ans:

They are also held together by strong intermolecular forces, like those tiny invisible springs we talked about earlier, but in a much stronger way. This fixed arrangement means the solid has a definite volume (it takes up a specific amount of space) and a definite shape (it doesn’t easily change its form). It’s like that box of marbles – it will always take up the same amount of space and keep its shape unless you apply a significant force to it.

17)Describe the molecular model for a liquid. I-low does it explain that a liquid has no definite shape, but has a definite Volume ?

Ans:  

Imagine the molecules in a liquid as being like a bunch of marbles in a container. They can slide past each other and move around quite a bit.  

This “loose” arrangement explains why a liquid has no definite shape – it will just take the shape of whatever container you pour it into. However, because the molecules are still quite close to each other and there’s a certain number of them, the liquid will always occupy roughly the same amount of space, giving it a definite volume. You can pour 100 ml of water into different shaped glasses, and it will always remain 100 ml, just taking on the new shape

18)A gas has neither a definite volume nor a definite shape. Describe the molecular model to explain it.

Ans:  

Imagine gas molecules as tiny, energetic little balls constantly zipping around in random directions and at high speeds. These molecules are quite far apart from each other compared to liquids or solids, and the forces holding them together are very weak. Because they have so much energy and so little attraction for each other, they don’t stay in any particular arrangement. That’s why a gas takes on both the volume and the shape of its container – its restless molecules just keep bouncing off the walls and each other, filling every nook and cranny!  

19)Distinguish between the three states of matter—solid, liquid and gas on the basis of their molecular models.

Ans:

Property	Solid	Liquid	Gas
Arrangement of Molecules	Molecules are very closely packed in a regular and orderly arrangement. They have fixed positions.	Molecules are close together but in an irregular and less orderly arrangement. They can move around and slide past each other.	Molecules are far apart from each other with no regular arrangement. They move randomly and freely in all directions.
Intermolecular Forces	Very strong attractive forces hold the molecules in their fixed positions.	Stronger attractive forces than in gases, but weaker than in solids. These forces allow molecules to stay close but move.	Very weak or negligible attractive forces between molecules. They move almost independently.
Movement of Molecules	Molecules can only vibrate about their fixed positions. They do not move from one place to another.	Molecules can vibrate, rotate, and move past each other. They have more kinetic energy than in solids.	Molecules have high kinetic energy and move randomly and rapidly, colliding with each other and the walls of the container.
Shape	Has a definite shape. It does not take the shape of its container.	Has no definite shape. It takes the shape of its container.	Has no definite shape. It takes the shape of its container and fills it completely.
Volume	Has a definite volume. It cannot be easily compressed.	Has a definite volume. It is difficult to compress.	Has no definite volume. It will expand to fill any container it occupies and can be easily compressed.
Density	Generally high because the molecules are closely packed.	Generally high, but usually slightly less dense than the solid state of the same substance.	Generally very low because the molecules are far apart.

Distinguish between solids, liquids and gases on the basis of their following properties :

(a) compressibility

(b) fluidity

(c) rigidity

(d) expansion on heating

Ans :

Property	Solid	Liquid	Gas
Compressibility	Highly Incompressible	Slightly/Practically Incompressible	Highly Compressible
Fluidity	Not Fluid	Fluid	Highly Fluid
Rigidity	Highly Rigid	Not Rigid	Not Rigid
Expansion on Heating	Slight Expansion	More Expansion than Solids	Significant Expansion

 21)What do you mean by the change of state of matter ? Explain:

(a) the change of a solid into a liquid at a constant temperature, and

(b) the change of a liquid into a gas at a constant temperature.

Ans :

The change of state of matter refers to the process by which a substance transitions from one physical form (solid, liquid, or gas) to another due to a change in temperature or pressure. During a change of state, the chemical composition of the substance remains the same; only the arrangement and movement of its constituent particles (atoms or molecules) change.

(a) The change of a solid into a liquid at a constant temperature:

• Explanation: When a solid is heated, its constituent particles (atoms or molecules) gain kinetic energy and vibrate more vigorously about their fixed positions in the lattice structure. As the temperature continues to rise, the vibrations become so intense that the particles overcome the strong intermolecular forces holding them in their rigid arrangement. At a specific temperature, known as the melting point, the particles gain enough energy to break free from their fixed positions and start moving more freely past each other.
• Constant Temperature: The change of state from solid to liquid occurs at a constant temperature (the melting point) under constant pressure. During the melting process, the heat energy supplied is used to overcome the intermolecular forces and change the state, rather than increasing the temperature of the substance. Once all the solid has melted, further heating will cause the temperature of the resulting liquid to rise.
• Example: When ice (solid water) is heated to 0°C (at standard atmospheric pressure), it starts to melt and turns into liquid water.

(b) The change of a liquid into a gas at a constant temperature:

Explanation: When a liquid is heated, its constituent particles gain kinetic energy and move more rapidly. This escape of molecules from the liquid surface is called evaporation, which occurs at all temperatures. However, when the temperature of the liquid reaches a specific point, known as the boiling point, the vapor pressure of the liquid becomes equal to the surrounding atmospheric pressure. At this point, vaporization occurs not just at the surface but throughout the bulk of the liquid, forming bubbles of gas that rise to the surface and escape.

Constant Temperature: The change of state from liquid to gas (boiling) occurs at a constant temperature (the boiling point) under constant pressure. Similar to melting, the heat energy supplied during boiling is used to overcome the intermolecular forces that hold the liquid molecules together and convert them into the more energetic gaseous state. The temperature remains at the boiling point until all the liquid has vaporized.

Example: When liquid water is heated to 100°C (at standard atmospheric pressure), it starts to boil and turns into water vapor (gaseous water). The temperature remains at 100°C until all the water has boiled away.