All substances and materials are made up of mater. Anything that has mass and occupies space is called matter. Anything which we can see, touch, smell or taste is matter. Thus, sight, feeling, heat, light, day, night, shadow and hearing are not examples of matter. Plants, human beings, animals, rivers, seas, mountains, sun stars, moon and clouds are examples of matter.
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Mass is defined as the quantity of matter contained in an object. It is expressed in kilograms. It can be measured by using a balance. Iron is heavier than cork. This is explained by saying that the mass of iron is greater than the mass of cork.
The space occupied by any mater is called its volume. The properties common to all matter are mass and volume.
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Two objects of different materials but having the same volume can have different masses. Consider two tumblers, one made of steel and the other of plastic. They have different masses even if they have the same size. Same size means same volume.
Mass of an object is found with the help of a physical balance. The difference of the two masses before and after inflating the balloon gives the mass of the air present in the balloon. Thus, air has both mass and volume and can be classified as matter.
States of Matter
Matter exists in three forms-solid, liquid and gaseous. These forms are called physical states of matter.
Iron and gold are solids; water and petrol are liquids; and oxygen and hydrogen are gases.
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Water can exist in three states-ice (solid), water (liquid) and steam (gaseous). All these states exist at different temperatures. When a piece of ice is heated, it changes into water (liquid). When water is heated further, it boils and changes into steam (gas). The reverse process also holds good. Steam on cooling changes into water. When water is cooled further, it changes into ice.
Melting:
The process of changing a solid into its liquid by heating is called melting. The melting point of a solid substance is defined as the constant temperature at which the solid melts and becomes a liquid. It is different for different solids. Ice melts at 0 degree Celsius. So, the melting point of ice is 0 degree Celsius
Boiling:
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The process of changing a liquid into its gaseous form by heating is called boiling. A liquid on heating starts boiling at a fixed (constant) temperature called the boiling point. It is different for different liquids. Water boils at 100 degree Celsius.
Evaporation:
Most of the liquids keep on changing slowly into vapors (gaseous state) at all temperatures. This is process is called evaporation. Ice with water in a closed bottle has some water vapor, showing the co-existence of all the three states of water.
Condensation:
On cooling, a gas changes into a liquid. The process of changing a gas (or vapors) into a liquid on cooling is called condensation.
Heat water in a beaker with a lid on it till it boils. When steam cools on the lid, it gets converted into water droplets. The formation of water droplets is due to condensation.
Freezing:
The process of changing a liquid into a solid on cooling is called freezing (or solidification). This change takes place at a constant (fixed) temperature called freezing point. Both freezing point of water and melting point of ice, i.e. 0 degree are equal.
Properties of Matter
Materials are classified on the basis of the following characteristics (or properties). Such properties help in their identification and classification.
1. State:
Matter can be classified on the basis of their state as solids, liquids or gases.
2. Solubility in water:
Some substances are soluble in water while others are insoluble in water. For example, salt and sugar are soluble in water. Sand and chalk powder do not dissolve in water.
3. Heaviness and lightness with respect to water:
Some substances float on water whereas some sink in water. A piece of paper and a few drops of kerosene oil float whereas a stone and a spoon sink in water.
4. Transparency and opaqueness:
There are some substances through which we can see e.g., glass and water. These are called transparent substances and such a quality is called transparency. There are some substances through which we cannot see. They are called opaque and this property is called opaqueness. Examples are a piece of iron sheet and a block of wood.
5. Attraction by a magnet:
Substances made of iron are attacked by a magnet. Materials which are attracted by a magnet are called magnetic materials.
6. Malleability:
Some substances can be beaten into very thin sheets. Such a property is called malleability. For example, iron, gold and silver are malleable.
7. Ductility:
The property of a substance of being drawn into wires is called ductility, and such a substance is said to be ductile. For example, iron, aluminum, gold and silver are ductile.
8. Brittleness:
There are some solid substances which break into pieces on hammering because they are hard and inflexible. Glass is brittle.
9. Combustibility:
Burning of substance to produce heat and light is called combustion and such a property of burning is called combustibility. Paper, wood, wax, hydrogen and petrol are combustible substances.
10. Volatility:
There are certain substances (liquids) which vaporize or evaporate quickly. The property of a liquid to get converted quickly into vapor is called volatility. Petrol, alcohol, spirit and ether are some examples of volatile substances. They are more volatile than water.
11 Melting point and boiling point:
These are fixed temperatures and can be used for classification.
12. Hardness or softness:
Hardness or softness of a substance is another property on the basis of which matter can be classified. Both graphite and diamond are forms of carbon. Graphite is a soft power. Diamond is the hardest substance.
13. Conduction of heat:
Matter can be classified on the basis of its ability to conduct heat. Matter is solid and liquid states can be a good conductor of heat. Gases are generally bad conductors of heat. You must have seen that cooking utensils have a plastic or wooden handle while rest of the utensil is made up of metal. The reason is: metals are good conductors of heat. In wood and plastic, the heat flows very slowly. They are bad conductors of electricity.
Paper, bakelite, cloth, etc., are bad conductors of electricity. Mercury which is used in thermometer is a good conductor of heat. Gases are bad conductors of heat.
14. Conduction of electricity
Metals are very good conductors of electricity. That is why electric wires are made of metals. In an electric bulb, the filament is made of a metal.
Rubber, paper, dry cloth, etc., are bad conductors of electricity. Water is also a bad conductor of electricity. But, water containing dissolved salts conducts electricity.
15. Diffusion:
Open a perfume bottle at one end of the room. You can smell its fragrance in the whole room. How does this happen?
This happens because gases diffuse in the air. The gaseous materials of the perfume mix with the air and we can smell it. If we light an incense stick in a room; we will find after some time that the whole room is full of its smell. The lighted forms vapor. The vapor mixed with air reaches us due to diffusion.
The rate of diffusion of gases is very fast. But different gases diffuse at different rates.