CBSE Class 6 Science Sorting Materials into Groups Exam Notes

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Sorting Materials into Groups

OBJECTS AROUND US
We saw that our food and clothes have so much variety in them. Not just food and clothes, there is a vast variety of objects everywhere. We see around us, a chair, a bullock cart, a cycle, cooking utensils, books, clothes, toys, water, stones and many other objects. All these objects have different shapes, colours and uses. Look around and identify objects that are round in shape. Our list may include a rubber ball, a football and a glass marble. If we include objects that are nearly round, our list could also include objects like apples, oranges, and an earthen pitcher (gharha). Suppose we were looking for objects that are edible. We might also find that some of those round shaped objects we just listed out, are also in this group.

Let us say, we wish to make a group of objects that are made of plastics. Buckets, lunch boxes, toys, water containers, pipes and many such objects, may find a place in this group. There are so many ways to group objects In the above examples we have grouped objects on the basis of their shape or the materials they are made from. All objects around us are made of one or more materials. These materials may be glass, metal, plastics, wood, cotton, paper, mud or soil. Can you think of more examples of materials?

WHAT ARE THINGS MADE OF?
You can see innumerable things around you. They look different and have properties different from each other. What are these things made of? Let us consider your pencil. It is made of wood, the ‘lead’ which is a combination of clay and substance called graphite, and paint. your eraser
is made of rubber. Your book is made of paper, ink and glue. A knife is made of steel and wood, or steel and plastic. Wood, steel, clay, graphite, paint, rubber, paper, ink, glue and plastic are examples of materials.

Materials are used to make different kinds of things or objects we use.
1. Same material can be used to make different kinds of things. For example, steel is used to make knives,utensils, cars, buildings, bridges.
2. Same object can be made from different kinds of mateirals. For example, a tumbler can be made of glass, plastic, thermocole, ceramic or paper.
3. Several objects can be made from a combination of several materials. For example, your pencil or your book.

What enables us to decide which mateiral is use to make a particular object? This depends on two things–what we want to use the object for; and the properties of the materials.

HOW MATERIALS ARE ALIKE

We have talked about the large number of things around us. As we know, they have properties different from each other. However, there are two properties which are common to all these things.

1. All materials occupy space. The amount of space something occupies is called its volume. You occupy more space than this book. So you have more volume than this book. Even the things you cannot see, such as air, occupy space.
2. All materials have mass. The amount of matter in an object is known as its mass. It can be measured by using a balance.

WHAT IS MATTER ?

Anything that occupies space and has mass is matter. It includes all substances from which the universe is made up of. The bones and flesh of your body, the clothes you wear, the food you eat, the water you drink and the air you breathe are all matter.

But then, what is not matter ? Feelings of love or sadness do not occupy space and do not have any mass. They are not matter. Radio or TV sets, or cellphones are matter, but the signals they receive are not. Can you think of some other things that are not matter ?

WHAT IS MATTER MADE UP OF ?

A piece of iron is matter. If an iron piece is broken, what happens ? It forms smaller pieces of iron. If we continue breaking this piece of iron it becomes smaller and smaller. But this must end somewhere. It should be possible to get the smallest piece of iron that cannot be broken any further. John Dalton, a scientist of the nineteenth century, named this smallest piece of iron, the iron atom. The smallest piece of gold is a gold atom.

Atoms are so small that they cannot be seen even by the most powerful microscope. Approximately, 40 lakh gold atoms, placed end to end, from a line only in a piece of 1 mm long. The smallest particle of gold and iron is the atom. But the smallest particle of water is not a water atom. Why? This is because water is made up of two different kinds of atoms, the atoms of hydrogen and atoms of oxygen. The smallest particle of water contains two atoms of hydrogen
and one atom of oxygen. These form one molecule of water.

Iron, gold, hydrogen and oxygen, whose smallest particles are atoms, are called elements. Substances, such as water, which are made up of two or more elements are called compounds. The smallest particle of a compound is a molecule.

There are about 117 different elements. Ninety-two of these occur naturally on the earth. The others have been made by scientists in laboratories artificially. Some common elements are: hydrogen, oxygen, chlorine, zinc, helium, sodium, silicon, silver, carbon, gold, sulphur, magnesium, phosphorus, nitrogen, aluminium and mercury.

Think of atoms like the letters of the alphabet. We group different letters to make words. Thousands of words can be made from just 26 letters. In the same way, atoms join together to make molecules. Millions of different kinds of molecules can be made from these 117 different kinds of atoms. That is why we see millions of compounds all around us. Sugar, chalk, vinegar, salt and water are all compounds. Their molecules are different from each other. This difference in the molecules is the reason why salt is ‘salty’ and sugar is ‘sweet’!

CLASSIFICATION
Take a look around yourself and try to make a list of things you can see. Are you able to list everything you see ? That would be quite a task for there are thousands and thousands of things around you. Some of these things may be living while some of them may be non-living. They may be of different shapes, sizes and colours. They may be made of same or different materials. There are even certain things that exist but you cannot see, such as air and microscopic germs. In what ways are the things you see different from each other? In what ways are they alike? Can you group things together according to certain properties ?

You will notice that Group A has living things whereas Group B has non-living things. grouping together things with similar properties is called classification.

Although living things share some common properties, they differ from each other in several ways. Living things are further classified into subgroups such as plants and animals. Each of these can be further classified based on certain properties. Animals can be classified into groups like insects, fish, amphibians, reptiles, birds and mammals. for example, All insects have six legs. But each group differs from other groups in some ways.

PROPERTIES OF MATERIALS

Have you ever wondered why a tumbler is not made with a piece of cloth? Recall our experiments with pieces of cloth in Chapter 3 and also keep in mind that we generally use a tumbler to keep a liquid. Therefore, would it not be silly, if we were to make a tumbler out of cloth! What we need for a tumbler is glass, plastics, metal or other such material that will hold water. Similarly, it would not be wise to use paper-like materials for cooking vessels.

APPEARANCE 

Materials usually look different from each other. Wood looks very different from iron. Iron appears different from copper or aluminium. At the same time, there may be some similarities between iron, copper and aluminium that are not there in wood.

LUSTRE

A metal spoon shines whereas a wooden spoon does not shine so much. Silk cloth has a shine whereas woollen cloth does not. We say that metal has more lustre than wood and that silk has more lustre than wool.

An iron rod may not appear lustrous. However, if you use sandpaper to remove the top layer you will see that it is lustrous. Some metals lose their lustre when exposed to air and moisture.

Materials can be classified on the basis of their lustre.

TEXTURE

Different materials feel different when you touch them, that is, they have different textures. For example, metal is hard and smooth whereas wool is soft and rough . Soft materials can be compressed or scratched easily. Hard materials are difficult to compress. Materials can be classified on the basis of their texture.

STATE

Most materials can be placed into one of the three groups: Solid, Liquid or Gas.

What is the difference between the three states? The difference lies in the way they change their shape and volume.

Solids do not easily change their shape or volume. You can move a box from one place to another but its shape and volume does not change.

Liquids change shape but not volume. Pouring milk from a jug into a tumbler causes milk to take the shape of the tumbler. But you still have the same amount of milk. Its volume does not change.

Gases easily change their shape and volume. If you pump air into a football, the air fills the football and takes its shape. Its volume changes. It takes up less space in the football than it did outside the football. 

SOLUBILITY OF SOLIDS IN WATER

An important property of water is its ability to dissolve many subsances in it. Most of the solids, liquids and gases dissolve in water. Substances which dissolve in water are said to be soluble and the property is called solubility. Substances which do not dissolve in water are said to be insoluble. For example common salt, sugar, glucose and vinegar are soluble in water whereas sand, chalk powder and wax are insoluble in water.

SOLUBILITY OF LIQUIDS IN WATER

Most of the liquids are soluble in water. However, some liquids such as edible oil, kerosene, petrol, etc. do not dissolve in water. The liquids which get mixed with water completely are called miscible liquids. Liquids which do not get mixed with water and form a separate layer on keeping for some time are called immiscible liquids.

SOLUBILITY OF GASES IN WATER

Like solids and liquids, some gases are soluble in water and others are insoluble in it. For example, oxygen and carbon dioxide are soluble in water. The oxygen dissolved in water helps aquatic plants and animals. Carbon dioxide dissolved in water helps the plants living in water for photosynthesis. Methane and nitrogen are examples of insoluble gases.

FLOTATION AND SINKING IN WATER

The substances which are heavier than water sink in it whereas substances lighter than water float over it. Thus you can classify materials into two classes: materials which float in water and materials which sink in water.

TRANSPARENCY

The materials through which we can see easily are called transparent materials and this property is called transparency. Some examples of transparent materials are glass, water, air and some plastics. Shopkeepers mostly keep biscuits, sweets, and other eatables in transparent containers of glass or plastics so that a customer can easily see these items to make his choice.

The materials through which we cannot see are called opaque and the property is called opacity. Wood, stone, metals are examples of such materials. The materials through which objects can be seen but not clearly are known as translucent. Frosted glass used in bathrooom window is translucent. Oiled paper, butter paper, muddy water are other examples of translucent materials.

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