Science for class- IX (NCERT)
Chapter-1 –Matter in our surroundings
1.1-Introduction
You all know about matter from our previous classes. In this chapter, you will study more deeply about the characteristics of different forms of matter and their properties.
1.2-What is matter?
Matter is anything that hassome massand occupies some space. A book, a table, a river, a fountain of steam , huge rocky mountains and even a small iron nail; all these look so different are all different forms of matter.
The ancient Indian scientists classified matter into five elements – air, water, earth, fire, and sky. But the modern scientists classify it on the basis of their physical and chemical structure. Matter has different forms and different forms of matter have different characteristics and different properties.
1.3-Different forms of matter.
Matter is present in three forms-
1.3.1-Solids
Solids are mostly hard and rigid. Their molecules have very little space or no space between them. They have fixed shape and fixed volume. This means that they are unable to change their shapes and they even break if extreme force is applied on them.They are least compressible.
But, what about a sponge? You can easily determine that a sponge is a solid, but you can easily change its shape. Then how is sponge a solid? Also, think of a rubber band which also comes in the categories of solid. You can stretch it easily according to your need, then how is a rubber called a solid?
- A sponge is obviously a solid but has tiny pours between its molecules which allow the passage of air through them. This creates space between the molecules of sponge and that’s why you can change its shape.
- A rubber band again is a solid, but its molecules are This allows the rubber band to be stretched according to your needs. However, the rubber band breaks if you try to stretch it over limit, so this proves that rubber band is a solid.
1.3.2-Liquids
Liquids are not rigid like solids but are fluid, which means they can flow. They have more molecular space than solids. They actually don’t possess any definite shape, but they do have a definite volume. They take the shape of the container in which they are kept. For example:- when you take a glass of water, the water inside the glass is in the shape of the glass. If you pour the water in a bowl, it changes shape to that of bowl. Liquids are more compressible than solids.
1.3.3-Gases
Gases have the least molecular space. They neither have any fixed shape, nor have any fixed volume. Some examples of gases are oxygen, hydrogen, nitrogen, etc. The molecules of gases keep moving. Because of the least molecular space, most gases are not visible. But they are present in all our surroundings. Even an empty jar container too has gas in it.
The molecules of gases in a container keep moving at high speed in random directions. Due to this random movement, they hit the walls of the container too. This way, they exert pressure on the walls of container in which they are kept.Gases are highly compressible and are available in compressed forms of Liquefied Petroleum Gas (LPG)
andCompressed Natural Gas (CNG), etc.
Below is the table of characteristics of different forms of matter:-
Table 1.1-Different characteristics of different types of matter.
