In the previous lesson, you have studied that the atoms are the smallest constituents of matter. But what is the structure of an atom? Why are atoms of different elements different? Let us try to find out the answers to some of these questions in this lesson.
We will start the study of this lesson by recapitulating the postulates of Dalton’s atomic theory .At that time, many Greek philosophers believed that the atoms cannot be further subdivided, i.e. they were structure less entities. But as you will study in this lesson, various developments such as the discoveries of sub-atomic particles such as electron, proton etc. led to the failure of this idea. Based on these discoveries, various atomic models were proposed by the scientists. In this lesson, we would discuss how various models for the structure of atom were developed and what were their main features. We would explain the success as well as the shortcomings of these models. These models tell us about the distribution of various sub-atomic particles in the atom. From the knowledge of structure of atom the arrangement of electrons around the nucleus can be obtained. This arrangement is known as electronic configuration. The electronic configurations of some simple elements are discussed in this lesson These electronic configurations would be useful in explaining various properties of the elements. The electronic configuration of an element governs the nature of chemical bonds formed by it. This aspect is dealt in lesson 5 on chemical bonding.