2. Molecular Theory of Matter

  Characteristics of Particles of Matter

• Particles of matter have space between them

→ Gas can be compressed a lot because of the space between their particles.

Activity:- take some water in a beaker and note its level. Dissolve some salt or sugar in it with the help of  a glass rod. The salt dissolves in the water but the level of water dose not change. This is because the particles of salt get the space between the particles of water.

→ Additionally you would notice that there is no rise of water level takes place when one or two teaspoon of sugar/salt is added into a glass of water, this is because sugar/salt particles get adjusted in the space between the particles of water and no rise in the water level comes in result.

• Particles of matter attract each other because of force of attraction.

Activity:- Take an iron nail, a piece of chalk and rubber band. Try breaking them hummering, cutting or stretching. It is more easier to break the chalk, less easier to break the rubber band and difficult to break the iron nail. this is because the particles in the iron nail are held together with greater force than in the rubber band or challk.

→ Force of attraction between particles of matter keeps the particles bonded together. Therefore attraction between particles of solid is greatest, between particles of liquid is moderate and between particles of gas is lowest.

→ Because of the lowest force of attraction between the particles of gas we can move our hand through

air easily. To move our hand in liquid, such as water, we have to apply some force, but a solid such as wood, we cannot move our hand.

→This is because the force of attraction between particles of gas is almost negligible, in liquid the forces of attraction is moderate but it is greatest in solid.

→ The force of attraction between particles of solid, liquid and gas can be arranged in decreases in order as follows:

Solid > Liquid > Gas

• Particles of matter are continuously moving –

Activity :- Take some water in a beaker and put a drop of blue or red ink slowly along the sides of the beaker. Leave it undisturbed for a few hours. The ink spreads evenly throughout the water due to the movement of the particles of water and ink.

The intermixing of two or more different types of matter on their own is called diffusion.

 • Matter is made up of small particles –

Activity :- Dissolve 2 —3 crystals of potassium permanganate in I OOml of water in a beaker. Take lOmI of this solution and dissolve in lOOmI of water. Take lOmI of this solution and dissolve In lOOmI of water. Repeat this process 5— 6 times. This shows that a few crystals of potassium permanganate can colour a large volume of water because there are millions of tiny particles in each crystal

Classification of states of matter

States of Matter

• Solid State

→ The space between the particles is very less.

→ The force of attraction between the particles is strong. Thus, particles in a solid are closely packed.

→ Solids maintain their shape even when they are subjected to external force i.e. they are rigid

→ Solids cannot be compressed.

→ The kinetic energy of the particles is very less and so solids have an orderly arrangement of particles. Therefore, solids have a fixed shape and volume.

• Liquid State

→ The space between the particles is slightly more as compared to solids, but still very less as compared to gases. The particles of a liquid can slip and slide over each other.

→ The force of attraction between the particles is strong enough to hold the particles together not strong enough to hold the particles in a fixed position.

→ Liquids do not have a fixed shape but have a fixed volume. Liquids take up the shape of the container in which they are poured.

→ The kinetic energy of the particles is more than that of solids. Thus, liquids have a disorderly arrangement of particles compared solids.

→ Liquids cannot be compressed much. The compressibility of liquids is almost negligible.

• Gaseous State

→ The particles are much farther apart from one another as compared to solids and liquids.They have a very disorderly arrangement of particles compared to the solids and liquids.

→ The force of attraction between the particles is negligible, hence particles of a gas move free in all the directions.Gases thus can mix or diffuse into other gases.

→ The particles of a gas have maximum kinetic energy. They move with high speed in all directions and can exert pressure on the walls of its container.

→ Gases neither have a definite shape nor a definite volume.They fill up the container completely

→ Gases can be compressed easily. Example: the LPG cylinders used at home and the CNG cylinder used in vehicles.