Atoms And Nuclei

a. Postulates of Bohr's Model:
Niels Bohr proposed a model for the atom in 1913, which explained the structure of the hydrogen atom. The two key postulates of Bohr's model are:
1. Electrons revolve in certain stable orbits around the nucleus without radiating energy. These orbits are called stationary orbits. This postulate was based on the fact that atoms do not emit energy continuously but only when electrons jump between orbits.
2. The energy of an electron in a stationary orbit is quantized and given by , where is the radius of the orbit, and and are constants. This postulate explains that only certain orbits with discrete energy levels are allowed.
b. Discovery of Nucleus Model of Atom:
The nucleus model of the atom was discovered by Ernest Rutherford in 1911. In his famous gold foil experiment, he demonstrated that the atom consists of a small, dense, positively charged nucleus at its center, with electrons orbiting around it.
Rutherford's Experiment:
In the experiment, alpha particles were directed at a thin sheet of gold foil. Most of the particles passed through, but a small fraction were deflected at large angles, indicating the presence of a dense center, which was identified as the nucleus. This was a pivotal moment in atomic theory, as it replaced the earlier plum pudding model of the atom.
Diagram of Rutherford's Nuclear Model: