Introduction to atomic models.
The basic unit of all matter is the atom. The Greek word 'atomos' means indivisible. The word 'atom' is derived from this word. The atom was considered an indivisible particle until the discovery of the proton, the electron and the neutron. J.J. Thomson’s cathode ray experiment revealed that the atom contains a negatively charged electron. J.J. Thomson proposed his atomic model that the atom is a sphere of positively charged particles and that the negatively charged electrons are packed in the sphere like seeds in a watermelon. Later, the results of Rutherford’s α-ray scattering experiments proved Thomson’s atomic model to be incorrect. Rutherford made α-rays fall on a thin gold plate. In this experiment i) Most of the α-rays penetrated through the gold plate. ii) Some of the α-rays were deflected at a small angle. iii) Very few α-rays were refracted at an angle of 180°. Based on the observation of the above experiment, Rutherford proposed the following atomic model. Th...