Matter in our Surroundings

Basic concepts

Every object is made up of lots of tiny particles and these particles are constantly moving.

States of matter

Matter can exist in three forms – solid, liquid and gas

The solid state

When matter is in its solid state, it has a definite shape, fixed volume and distinct boundaries. Rigidity and incompressibility are other features of solid matter.

The liquid state

Liquids do not have a definite shape or boundary, but they have a fixed volume. Fluidity and low compressibility are other features of liquid matter.

The gaseous state

When matter is in the gaseous state, it does not have a definite boundary, volume or shape. The gaseous state of matter is also characterized by features such as high compressibility and fluidity.

We have already seen that matter is made of tiny particles. These tiny particles are closely packed in solids and loosely packed in liquids. In gases, these particles are far apart.

Questions and answers

1. What exactly is matter?

Anything that has mass and occupies space is matter. Everything in the universe is made up of matter. Examples are: wood, water, plants, minerals, books, food etc.

2. What is intermolecular force of attraction?

The tiny particles that make up matter attract one another. This force of attraction between particles of matter is called intermolecular force of attraction. Since the intermolecular force of attraction is affected by temperature and pressure, we can change the state of matter by changing the temperature or pressure.

3. What is melting point?

Melting point is the temperature at which a solid changes into a liquid at atmospheric pressure.

4. Define latent heat of fusion

Latent heat of fusion is the amount of heat consumed when 1 kg of a solid changes into a liquid at a constant temperature.

5. What is boiling point?

Boiling point is the temperature at which a liquid changes into vapour at atmospheric pressure.

6. Define latent heat of vaporization

Latent heat of vaporization is the amount of heat consumed when 1 kg of a liquid changes into its gaseous state at a constant temperature.

7. What is sublimation?

Typically solids go through the liquid state before they can change into their gaseous state. Sublimation refers to the change of state wherein a solid changes into its gaseous state or a gas changes into its solid state without going through the liquid state.

8. What is evaporation?

Evaporation is a type of vaporization that occurs on the surface of a liquid as its changes into its gaseous form.

9. Salt and sugar look similar. Why are these substances classified as different substances?

Appearance is not the only criterion used to classify substances. Other properties such as density, thermal capacity, conductivity, boiling or melting point and other chemical properties are also used to classify substances. Since the chemical and physical properties of sugar and sodium chloride are different, they are classified as different substances.

10. Why is air considered as matter?

Air is considered as matter because it has mass and occupies space.

11. Which of the following is an example of matter?

(i) air, (ii) sky, (iii) fire, (iv) work, (v) leisure

Answer: air

12. When sugar or salt dissolves in water, does the water level increase? Why?

No. When sugar or salt dissolves in water, there is no change in water level. Water is a liquid with loosely packed particles. When salt dissolves in water, salt particles occupy the space between water particles. Consequently, there is no increase or decrease in the level of water.

13. Explain with the help of an activity which shows that particles of matter are very very small (CBSE 2012)

Here is a simple experiment that proves that particles of matter are very very small.

Step 1: Dissolve 2-3 crystals of potassium permanganate in 100 ml of water.

Step 2: Take out 10 ml of water from this solution and add it to 90 ml of clear water.

Step 3: Keep diluting the solution by repeating this step 8 times.

Inference: The water remains coloured till the last dilution and this clearly proves that the particles of matter are very very small.