Read First –
Matter around us exists mainly in three states –
This can be understood with the help of three forms of water – ice, water and water vapor .
Take a big piece of ice in a beaker at room temperature. Observe the ice.
Solid ice has definite shape and fixed volume. After some time, the ice converts into liquid water. Liquid water has no fixed shape but has a fixed volume as it takes the shape of the beaker. On heating liquid water on a burner, it converts into water vapor. Water vapor has no fixed shape and no fixed volume. It can move easily and can occupy all the space available to it.
It means, water can exists in three states (or physical states) of matter–
• Solid, as ice,
• Liquid, as the familiar water, and
• Gas, as water vapor.
The three physical states of water – ice, liquid water and water vapor have the same type of particles or made up of the same matter, even then they show different properties in their different physical states. Why?
This is because the arrangement of particles in solid, liquid and gaseous states of water are different.
Classification of matter on the basis of their physical states
1. The Solid State –
Observe the following articles – a table, sugar, salt, pen, notebook, rubber band, sponge etc.
All the above examples are of solids, if they satisfy following conditions.
(a) Solids are generally rigid.
- Tendency of solids to resist any change in their shape on applying external force is called rigidity. It means they have a definite shape and distinct boundaries.
For e.g. table, sugar, salt, pen, notebook etc.
- Some solids like rubber are elastic and can change their shape by aplying an external force. However, on removing the force, they regain the same shape. If excessive force is applied, they break.
- A sponge has minute holes, in which air is trapped. When we press it, the air expels out and the sponge compresses.
(b) Solids are almost in-compressible.
- They have negligible compressibility and fixed volumes. Solids have a tendency to maintain their shape when subjected to outside force. Solids may break under force but it is difficult to change their shape, so they are rigid.
- The particles of solids are so closely packed that it is extremely difficult to compress them further. The inter-particle space in solids is extremely small.
(c) Solids are quite strong.
- They are not easily stretched as their particles are very close to each other and have very large force of attraction.
(d) Solids have high densities.
- So they are heavy. This is because the particles of solids are tightly packed so they occupy small but definite volume.
(e) Solids do not flow.
(f) Solids do not diffuse or mix readily with one another on their own.
- The reason is particles of solids are bound with very strong force of attraction that resist them to move freely and also they have very little empty space between their particles.
- But solids can diffuse more readily in liquids because liquid particles have more empty spaces that can be occupied by the solid particles.
Thus, all the common properties of solids can be explained on basis of their arrangement of particles. That is they are closely packed and have extremely strong force of attraction.
2. The Liquid State –
Observe the following examples – milk, water, honey, kerosene, cooking oil, juice, cold drink etc. All the above examples are of liquids as they have following properties –
(a) Liquids have no fixed shape but have a fixed volume.
- When we pour a liquid from one container to another, they take up the shape of that container but volume remains same.
(b) Liquids are generally fluid.
- Liquids can easily flow and change shape, so they are not rigid like solids. The tendency of liquids to flow is called fluidity.
(c) Liquids are difficult to compress by applying pressure.
- This is because although the particles are not closely packed as in solids even they are very close to each other.
(d) The densities of liquids are slightly lower than the densities of solids.
(e) In general, liquids have a tendency to diffuse into one another.
- It also depends on the nature of liquids.
For e.g.- water and milk / alcohol particles diffuse and mix easily whereas oil and water do not mix.
- The rate of diffusion of liquids is higher than that of solids. This is due to the fact that in the liquid state, particles move freely and have greater space between each other as compared to particles in the solid state. The solids and gases also tend to diffuse in liquids.
For e.g., Sugar / salt (solid) mix in water; Oxygen from air can diffuse in water. This oxygen is used for breathing of aquatic animals in water.
(f) The inter-particle attraction in liquids is much less than in solids.
This is because in the liquid state, particles can move freely and have larger empty space between each other as
compared to particles in the solid state.
Thus, all the common properties of liquids can be explained on basis of that the inter-particle attraction in liquids is much less than in solids.
3. The Gaseous State –
Examples of gas are oxygen, hydrogen, nitrogen, chlorine, air etc.
(a) Gases have a definite mass, but no fixed shape or volume.
(b) Gases are generally fluid.
- They occupy the entire space of the container in which they are stored.
(c) Gases are highly compressible as compared to solids and liquids.
- This is because the inter-particle spaces are very large in gases. It is very easy to compress a gas by applying external pressure.
For e.g. – the liquefied petroleum gas (LPG) cylinder we use for cooking; the oxygen supplied to hospitals in cylinders are compressed gas. Due to their high compressibility, large volumes of a gas can be compressed into a small cylinder and transport easily.
(d) The densities of gases is almost negligible as compared to solids and liquids.
- That is why a gas is much lighter than the same volume of a solid or a liquid.
(e) The inter-particle attraction is the least in gases.
(f) When two or more gases are mixed, their particles rapidly diffuse into each other and form a homogeneous mixture.
Example – the smell of hot cooked food reaches us in seconds. The high speed of particles and large inter-particle spaces account for this property.
(g) A gas exerts pressure on all sides of the container which holds the gas.
- This is because the particles move about randomly at high speed. Due to this random movement, they hit each other and also the walls of the container.The amount of pressure is related to the energy of the gas and the amount of gas. The higher the energy, the more pressure is exerted, and the more gas is contained, the more pressure is exerted. Example – air in the balloon, air in a tyre tube.
– The reduction in the volume of a substance on applying external pressure to it is called compressibility.
– A substance that exists in the gaseous state under ordinary conditions of temperature and pressure is known as gas.
For e.g. oxygen, hydrogen, chlorine etc.
– A substance that exists in the solid or liquid state under ordinary conditions of temperature and pressure, but changes into its gaseous state under specific conditions is known as vapor.
For ex. water at 100°C turns in to water vapor.
Quiz – Check how much have you understood –
Read Next –