Notes

Kinetic Molecular Model of Matter:

1. The matter is made up of particles called molecules.
2. The molecules remain in continuous motion.
3. Molecules attract each other.

 

Characteristics of Molecular Model of Matter:

The kinetic molecular model is used to explain the three states of matter - solid, liquid, and gas.

a. Solids:

1. Solids such as stone, metal spoons, pencils, etc. have fixed shapes and volumes.
2. Their molecules are held close together by strong forces of attraction.
3. Molecules of solids vibrate about their mean positions but do not move from place to place.

b Liquids:

1. The distances between the molecules of a liquid are more than in solids. Thus, attractive forces between them are weaker.
2. Like solids, molecules of a liquid also vibrate about their mean position but are not rigidly held with each other.
3. Due to the weaker attractive forces, they can slide over one another. Thus, liquids can flow.
4. The volume of a certain amount of liquid remains the same but because it can flow hence, it attains the shape of a container in which it is put.

c. Gases:

1. Gases such as air have no fixed shape or volume. They can be filled in any container of any shape.
2. Their molecules have random motion and move with very high velocities. In gases, molecules are much farther apart than solids or liquids. Thus, gases are much lighter than solids and liquids.
3. They can be squeezed into smaller volumes.
4. The molecules of a gas are constantly striking the walls of a container. Thus, a gas exerts pressure on the walls of the container. (P ∝E)

 

 

d. Plasma – The fourth state of matter:

1. Production/Formation of Plasma:

The kinetic energy of gas molecules goes on increasing if a gas is heated continuously. This causes the gas molecules to move faster and faster. The collisions between atoms and molecules of the gas become so strong that they tear off the atoms. Atoms lose their electrons and become positive ions. This ionic state of matter is called plasma. Plasma is also formed in gas discharge tubes when an electric current passes through these tubes.

2. Plasma is called the fourth state of matter in which a gas occurs in its ionic state. Positive ions and electrons get separated in the presence of electric or magnetic fields.

3. Plasma also exists in neon and fluorescent tubes when they glow.

4. Most of the matter that fills the universe is in the plasma state.

5. In stars such as our Sun, gases exist in their ionic state.

6. Plasma is a highly conducting state of matter. It allows electric current to pass through it.

 

 

USEFUL INFORMATION

Density of various substance
Substances	Density in $kgm^{-1}$
Air	1.3
Foam	89
Petrol	800
Cooking Oil	920
Ice	920
Water	1000
Glass	2500
Aluminum	2700
Iron	7900
Copper	8900
Lead	11200
Mercury	13600
Gold	19300
Platinum	21500

 

USEFUL INFORMATION

1 metre cube (1 m³) = 1000 litre
1 litre = $10^{-3}$
1 cm³ = $10^{-6}$
1000 $kgm^{-3}$ = 1 $gcm^{-3}$