Particulate Nature of Matter

PARTICULATE NATURE OF MATTER

•  Matter is made up of small particles

The particle nature of matter can be demonstrated in activity 4.1:

ACTIVITY4.1

To demonstrate particle nature of matter

1. Take about 50 cm3 water in a 100 cm3 beaker.

2. Mark the level of water.

3. Add some sugar to the beaker and stir with the help of a glass rod.

4. Observe the change in water level.

Fig. 4.1. Dissolution of sugar in water. In solution particles of sugar are present in the spaces between particles of water

It is observed that the crystals of sugar disappear. The level of water remains unchanged. These observations can be explained by assuming that matter is made up of small particles. On dissolution, the particles of sugar get distributed into the spaces between particles of water.

• The constituent particles of matter are extremely small in size

The following activity demonstrates that the constituent particles of matter are very small

ACTIVITY 4.2

To demonstrate that the particles of matter are very small

1. Take a 250 cm3 beaker and add 100 cm3 water to it

2. Now add 2-3 crystals of KMnO4 and stir with a glass rod in order to dissolve the crystals.

3. Take 10 cm3 of this solution and add to 100 cm3 of water taken in another beaker.

4. Take 10 cm3 of this diluted solution and put into 100 cm3 of water taken in still another beaker.

5. Repeat this process 10 times. Observe the colour of the solution in the last beaker.

It is observed that the water in the last beaker is still coloured but the intensity of colour becomes light It indicates that KMnO4 crystal contains millions of tiny particles, some of which are still present even in the last beaker after so much dilution.

• There are spaces between particles of matter In activity 4.1 we observed that when sugar is dissolved in water, the volume of the liquid remains unchanged. During dissolution, the particles of sugar get into the spaces between the particles of water. As a result, they get evenly Distributed and there is no noticeable change in volume. Similarly, when KMnO4 is dissolved in water, its particles get evenly distributed throughout the bulk of water. This is indicated by uniform colour of the solution. This indicates that there are spaces between particles of matter. The particles of KMnO4 get uniformly distributed in the spaces between water molecules.

• The particles of matter are continuously moving The motion of particles of matter can be demonstrated by the following practical activities:

ACTIVITY 4.3

To demonstrate motion of particles of matter

Place a bottle containing concentrated aqueous solution of ammonia in a corner of the room. Remove the stopper.

What do you observe?

It is observed that ammoniacal smell can be sensed sitting at a distance.

It demonstrates that the particles of ammonia are moving. Due to this motion they are able to reach the observer.

Similarly, if an incense stick is lighted and placed in one comer of a room, its pleasant smell spreads in the whole room quickly. It demonstrates that the particles of matter possess motion. A burning incense stick produces some gases (vapour) having pleasant smell. The particles of these gases due to motion spread in the entire room and their presence can be felt by sensing the smell.

ACTIVITY 4.4

To demonstrate motion of particles in water and ink

1. Take a 250 cm3 beaker and add about 100 cm3 of water to it.

2. Put a drop of blue ink to the water taken in the beaker. What do you observe?

It is observed that the blue ink gets evenly distributed in the water.

This demonstrates that the particles of water and ink possess motion.

Due to motion of the particles, the particles of the two liquids are able to mix with each other.

ACTIVITY 4.5

To demonstrate that the kinetic energy of particles increases with increase in temperature

1. Take two beakers. To one beaker add 100 cm3 of cold water and to the other beaker add 1 00 cm3 of hot water.

2. Now add a crystal of potassium permanganate to both the beakers.

What do you observe?

It is observed that the purple colour of potassium permanganate starts spreading and after sometime the entire solution becomes purple. The rate of mixing is faster in case of hot water. This experiment demonstrates that the particles of matter possess motion and that the kinetic energy of the particles increases with increase in temperature

The above activities demonstrate that when two different forms of matter are brought in contact they intermix spontaneously. This intermixing is possible due to motion of the particles of matter and also due to the spaces between them. The intermixing takes place due to movement of particles of one form into the spaces between the particles of the other form of matter. This spontaneous intermixing of particles of two different types of matter is called diffusion. The rate of diffusion becomes faster with increase in temperature because at higher temperature, the particles have more energy and hence move faster.

• Particles of matter attract each other

There are forces of attraction between particles of matter. The evidence for forces of attraction in gases is obtained from the fact that they can be liquefied by applying pressure.

The important characteristics of particles of matter are summarized below:

1. The particles of matter are extremely small in size.

2. The particles of matter have spaces between them.

3. The particles of matter are continuously moving.

4. The particles of matter attract each other.

The constituent particles of matter may be atoms, molecules or ions. Some examples are given below in tabular form:

Constituent particles               Examples

1. Atoms                                 Argon, neon, helium, diamond

2. Molecules                            Sucrose , glucose,urea,methane carbon(IV) oxide

3. Ions                                     Sodium chloride, magnesium oxide, zinc sulphide