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                    1. Introduction Matter is made up of one or different type of elements. Under normal conditions no other element exists as an  independent atom in nature, except noble gases. However, a group of atoms is found to exist together as one species having characteristic properties. Such a group of atoms is called a molecule. Obviously there must be some force which holds these constituent atoms together in the molecules. The attractive force which holds various  constituents (atoms, ions, etc.) together in different chemical species is called a chemical bond. Since the formation of chemical compounds takes place as a result of combination of atoms of various elements in different ways, it raises many questions. Why do atoms combine? Why are only certain combinations possible? Why do some  atoms combine while certain others do not? Why do molecules possess definite shapes? To answer such questions different theories and concepts have been put forward from time to time.

               1. Introduction The Periodic Table as it stands today and the Modern Periodic Law. We will also learn how the periodic classification follows as a logical consequence of the electronic configuration of atoms. Finally, we shall examine some of the periodic trends in the physical and chemical properties of the elements.    WHY DO WE NEED TO CLASSIFY ELEMENTS ? We know by now that the elements are the basic units of all types of matter. In 1800, only 31 elements were known. By 1865, the number of identified elements had more than doubled to 63. At present 118 elements are known. Of them, the recently discovered elements are man-made. Efforts to synthesise new elements are continuing. With such a large number of elements it is very difficult to study  individually the chemistry of all these elements and their innumerable compounds individually. To ease out this problem, scientists searched for a systematic way to  organise their knowledge by classifying the elements. Not

                1. Introduction The existence of atoms has been proposed since the time of early Indian and Greek philosophers (400 B.C.) who were of the view that atoms are the fundamental building  blocks of matter. According to them, the continued subdivisions of matter would ultimately yield atoms which would not be further divisible. The word ‘atom’ has been  derived from the Greek word ‘a-tom io’ which means ‘uncut-able’ or ‘non-divisible’. These earlier ideas were mere speculations and there was no way to test them experimentally. These ideas remained dormant for a very long time and were revived again by scientists in the  nineteenth century. The atomic theory of matter was first proposed on a firm scientific basis by John Dalton, a British school  teacher in 1808. His theory, called Dalton’s atomic theory, regarded the atom as the ultimate particle of matter. Dalton’s atomic theory was able to explain the law of conservation of mass, law of constant  composition and law of

                       1. Introduction

       1. DEVELOPMENT OF CHEMISTRY Chemistry, as we understand it today, is not a very old   discipline. Chemistry was not studied for its own sake, rather   it came up as a result of search for two interesting things: i. Philosopher’s stone (Paras) which would convert  all baser metals e.g., iron and copper into gold. i i.‘E lex i r of life’ which would grant immortality. People in ancient India, already had the knowledge of many   scientific phenomenon much before the advent of modern science. They applied that knowledge in various walks of   life. Chemistry developed mainly in the form of Alchemy   and Iatrochemistry during 1300-1600 CE. Modern   chemistry took shape in the 18th century Europe, after a  f ew centuries of alchemical traditions which were introduced in Europe by the Arabs. Other cultures – especially the Chinese and   the Indian – had their own alchemical traditions. These included much knowledge of chemical  processes and techniques.  In ancient India, chemistry w

                             1. INTRODUCTION In this topic we will study about the waves. A material medium provides   such an example. Here, elastic forces bind the constituents   to each other and, therefore, the motion of one affects that of   the other. If you drop a little pebble in a pond of still water,   the water surface gets disturbed. The disturbance does not   remain confined to one place, but propagates outward along a circle. If you continue dropping pebbles in the pond, you   see circles rapidly moving outward from the point where the   water surface is disturbed. It gives a feeling as if the water is   moving outward from the point of disturbance. If you put   some cork pieces on the disturbed surface, it is seen that the cork pieces move up and down but do not move away   from the centre of  disturbance. This shows that the water mass does not flow outward with the circles, but rather a   moving disturbance is created. Similarly, when we s

                            1. INTRODUCTION You have already learnt about some of them, e.g., rectilinear   motion and motion of a projectile. Both these motions are   non-repetitive. We have also learnt about uniform circular   motion and orbital motion of planets in the solar system. In   these cases, the motion is repeated after a certain interval of   time, that is, it is periodic. In your childhood, you must have   enjoyed rocking in a cradle or swinging on a swing. Both   these motions are repetitive in nature but different from the   periodic motion of a planet. Here, the object moves to and fro   about a mean position. The pendulum of a wall clock executes   a similar motion. Examples of such periodic to and fro   motion abound: a boat tossing up and down in a river, the   piston in a steam engine going back and forth, etc. Such a   motion is termed as oscillatory motion. In this chapter we   study this motion.OSCILLATIONS   The study of oscillatory motion is bas

                    1. INTRODUCTION In this topic we will know about kinetics theory. Boyle discovered the law named after him in 1661. Boyle,   Newton and several others tried to explain the behaviour of   gases by considering that gases are made up of tiny atomic   particles. The actual atomic theory got established more than   150 years later. Kinetic theory explains the behaviour of gases   based on the idea that the gas consists of rapidly moving   atoms or molecules. This is possible as the inter-atomic forces, which are short range forces that are important for solids   and liquids, can be neglected for gases.   The kinetic theory   was developed in the nineteenth century by Maxwell,   Boltzmann and others. It has been remarkably successful. It   gives a molecular interpretation of pressure and temperature of a gas, and is consistent with gas laws and Avogadro’s   hypothesis. It correctly explains specific heat capacities of   many gases. It also relates measura