Std 8 ch 5 THE STRUCTURE OF AN ATOM
5. THE STRUCTURE OF AN ATOM 5 THE STRUCTURE OF AN ATOM points to remember : 1. Dalton’s Atomic model : Dalton proposed that matter is made up of very small particles. These small particles are called atoms. An atom is a hard and solid ball. Being the smallest unit of matter, it is indivisible. 2. Thomson’s atomic model : Thomson proposed that the atom is a homogeneous sphere of positive charge in which electrons are embedded. Electrons are negatively charged particles. As the positive and negative charges are equal, the atom as a whole does not have any resultant charge. 3. Rutherford’s atomic model : The centre of the atom is called the nucleus and it has positive charge. Most of the mass of the atom is concentrated in the nucleus. Electrons bear negative charge. They revolve around the nucleus in specific orbits. The nucleus is very very small as compared to the size of the atom. 4. The structure of the atom : The fundamental particles in atom