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What is Chemistry?
Matter is anything that takes up space and has mass. Everything you see around us is made up of matter. What is matter made of?
In 1808, John Dalton was able to show that matter is made up atoms or atoms combined in molecules. An atom is the smallest unit of an element that can exist alone or in combination with other atoms of the same or different elements. There are three kinds of particles that have been found to form the basic structure of matter. These particles are called atomic and sub- atomic particles they include:
PROTONS: Protons are positively charged particles. The positive electron change on each proton is the same as the negative charge on electron.
ELECTRONS: Electrons are extremely light particles. Each electron has unit negative electric charge.
NEUTRONS: These are particles that are electrically neutral. A neutron has the same mass as a proton.
A molecule is the smallest particle of an element or a compound and has all the properties of that element or compound.
ELEMENTS: A substance made of just one kind of atom is known as element. Iron is an element. Iron is the only element made up of iron atoms. Gold is an element made up of gold atoms. So far 115 elements are known out of which 92 are naturally- occurring in the earth’s crust.
On the basis of physical and chemical properties, elements can be classified into two main groups: metals and non- metals. About 75 per cent are metals. Metals are usually shiny. They are good conductors of heat and electricity. They can be bent or hammered into different shapes. On the other hand non- metals are generally liquids and gases at room temperature. Non- metal solids usually have dull shapes. They are poor conductors of heat and electricity.
COMPOUNDS: When atoms of different elements combine chemically, they form compounds. Scientists has discovered about four million compounds formed from two or more of 115 elements.
For example: All sugars are made up of three kinds of elements. These elements are carbon, hydrogen and oxygen. Each compound of sugar form when a certain number of carbon, hydrogen and oxygen atoms join in a certain way.
PHYSICAL AND CHEMICAL CHANGES
Matter is always changing. For example water is not always liquid. You can freeze to make it solid ice. You can also boil water to make it gas. A change in matter in which the individual molecules are not arranged is known as a PHYSICAL CHANGE. It is a reversible and a temporary change.
Some of the examples are:
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Drying of wet clothes.
Melting of wax or butter.
Dissolving a solid into a liquid.
Stretching of a rubber band.
Hammering of metals to form sheets.
Glowing a electric bulb passing on electric current.
A change in matter in which one kind of molecules is changed into another kind of molecules with new properties is called CHEMICAL CHANGE. The number of atoms of each kind of molecules remains the same before and after the chemical change. It is a permanent change.
Some of the examples are:
Charring of sugar.
Cooking of food.
Formation of curd from milk.
Digestion of food.
Ripening of fruits.
Germination of seeds.
IMPORTANCE OF CHEMISTRY
Everything which surrounds us is a composition of chemicals. The subject chemistry helps us to understand the behaviour of chemicals. The changes that take place in the external environment are due to the chemical reactions. The following highlights the importance of chemistry and its uses.
Nitric acid that has nitrogen and oxygen is used to prepare nitrate salts. Nitrates of silver find use in photography.
Oxygen is used by plants and animals for their survival. Oxygen supports combustion reactions in factories, homes, aeroplanes etc.
Platinum, gold and silver are called noble metals. They are used for making jewellery. Silver and gold are also used for making coins and medals.
Copper, aluminium and iron are being good conductors of electricity are used in preparing wires. Domestic tools, utensils and machinery are also prepared from them.
Red phosphorus is used for preparing matchsticks and fireworks. Phosphorus is useful in killing rats for preserving food grains. It is also used in chemical fertilisers.
Aluminium foil is used in packing material for some food products, medicines, chocolates, cigarettes etc.
Chlorine has the ability to kill the germs. Hence, it is used in water purification. Tincture iodine is used on the wound in the body. It is the solution of iodine in alcohol that has antiseptic properties.
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