States of Matter

1.0Solids - Shape, Volume, Compressibility, Fluidity

Collect the following articles- a pen, a book, a needle etc. All of them are examples of solids. 

We can observe that all these have a definite shape, distinct boundaries and fixed volumes.

The intermolecular force is very strong in solids. So the molecules are very closely packed. They cannot move away from one another and can only vibrate about fixed positions. These facts explain the general properties of solids. 

Pen, Book, Needle and wooden stick

(i) A solid has a fixed shape and a fixed volume : This is because the molecules cannot move closer to or away from each other. 

Different shapes of solids

(ii) Solids generally cannot be compressed : That is, their volumes cannot be reduced by  applying pressure on them. The intermolecular space in solids is negligible. So, the molecules cannot be pushed closer. However, a porous solid like a loaf of bread has air spaces, which make it easily compressible.

(iii) A solid does not flow : This is because the molecules are so tightly held that they cannot  slip over one another.

(iv) A solid expands or contracts very little on being heated or cooled : On being heated, the molecules become more energetic and vibrate to a greater extent. However, they do not leave their positions entirely and so the expansion is small. When you heat a pan or a nail, it expands so little that you do not notice it. But when a liquid such as the mercury in a thermometer gets heated, it expands quite a bit.

2.0Liquids - Shape, Volume, Compressibility, Fluidity

Collect the following- water, cooking oil, milk, juice, a cold drink etc. All of these are liquid forms of matter. The intermolecular force in liquids is weaker than in solids. So, the molecules are farther apart and are not tightly held in their positions. Therefore, they can slip over one another. In other words, liquids can flow. 

Liquids Have The Following General Properties

A Liquid Has no Fixed Shape but Has Fixed Volume

It takes the shape of the container it is in. Four equal quantities (say 300 mL) of water is poured into containers of different shapes. In each case water will take the shape of the container. In every case the volume of water will remain the same, i.e., 300 mL.

Liquid water takes the shape of its container

The shape of a liquid changes as the molecules can slip over one another and settle down   to assume the shapes of the containers into which it is poured. However, the volume does not change as the molecules cannot come closer to or move away from each other.

We observe that the water has acquired the shape of all the three containers.                                                                        

A liquid can be compressed only to a small extent

The intermolecular space in liquids   is not very large. So the molecules can be pushed closer only to a limited extent.

A liquid can flow

The intermolecular force being weak, the molecules can slip over one another.

A liquid expands or contracts more than a solid

When a liquid is heated, the molecules move more vigorously and go farther from each other, and the liquid expands.

Take an example, Fill a narrow-mouthed bottle with coloured water. Fix a transparent straw in the bottle with the help of a sealant (e.g., M-Seal). Now place the bottle in a bowl of hot water.The water in the bottle will expand and rise in the straw. When you take the bottle out of the hot water, the water inside it will cool. It will contract, and the level of the water in the straw will fall. This shows that Liquids expand on heating and contract on cooling.

All liquids do not mix with each other

Water mixes with milk, honey and alcohol, but  not with oil. Liquids which mix with each other are called miscible liquids. And those which do not are called immiscible liquids. Miscible liquids: Alcohol and water Immiscible liquids: Water and many types of oils

3.0Gases - Shape, Volume, Compressibility, Fluidity

Oxygen, Nitrogen, water vapour etc. these all are gaseous state of matter. As you know, the intermolecular space is much larger and the intermolecular force is much weaker in gases than in solids and liquids. Because of the very weak intermolecular force, gas molecules can move about much more freely than solid and liquid molecules. In fact, they can move about in all directions.

The same gas has acquired different shapes depending on the shape of the balloon.

Gases have the following properties.

A gas has neither a fixed volume nor a fixed shape

It assumes the volume and shape of the container. Remember that, unlike a liquid, it occupies the entire volume of the container. This is because the molecules are free to move in all directions.

The molecules of gas spread in the entire space of the containing vessel on account of high energy and practically low intermolecular forces, hence fill the entire space of the vessel.

Gases can be compressed to a much larger extent than solids and liquids

This is because the molecules are very far apart in gases, and come much closer when pressure is applied. You can push in a lot of air into the small volume of your cycle tube because air is very compressible.                                                                    

Examples: 

1. The liquified petroleum gas (LPG) cylinder we use in our home for cooking.

2. The oxygen supplied to hospitals in cylinders in liquid form by compressing it.

3. Compressed natural gas (CNG) is used as fuel in vehicles.             

Diffusion of particles of burned incense stick shows that particles of matter are in a state of continuous motion

A gas expands or contracts to a great extent on being heated or cooled

On being heated, gas molecules become more energetic and move even farther apart. In other words, the gas expands. Because the intermolecular force is very small, the expansion is great. On being cooled, gas molecules become less energetic and move less vigorously. This brings them close enough for intermolecular attraction to come into play. This brings the molecules closer still. 

The intermolecular space is considerably reduced. In other words, the contraction is great. In the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container.

Gases freely mix with one another because the molecules of a gas can easily occupy the large intermolecular spaces of another gas

This phenomenon is known as diffusion. The fragrance of a perfume spreads by the diffusion of its vapours through air. You can observe diffusion by doing the following activity. 

The aroma of cooked food reaches us from the kitchen. The smell of hot cooked food reaches us in seconds, compare this with the rate of diffusion of solids and liquids. Due to high speed of particles and the large space between them, gases show the property of diffusing very fast into other gases. 

4.0 Comparison of States of Matter