Rutherford model laid the foundation of the model picture of the atom. However it did not tell anything as to the position of the electrons and how they were arranged around the nuclears.
Rutherford recognised that electrons were orbiting around the nuclears. But according to the classical laws of pht an electron moving in a field of force like that of nucles, would give off radiations and gradually collapse into the nuclears. Thus Rutherford model failed to explain why electrons did not 🚫 do so.
Neils Bohr, a brilliant Danish Physicist, pointed out that the old laws of Physics just did not 🚫 work in the submicroscopic world of atom. He closely studies the behaviour of electrons, radiations and atomic spectra. In 1913 Bohr proposed a new model of atoms based on the modern Quantum theory of energy.
With his theorical model he was able to explain as to why an orbiting electron did not collapse into the nucleus and how the atom spectra were caused by the radiations emitted when electron moved from one orbit to the other.
Therefore to understand the Bohr theory of the atomic structure, it a first necessary to acquaint ourselves with the nature of electromagnetic radiation and the atomic spectra and also the Quantum theory of energy.
What is Mass Number?
The total number of proton and neutrons in the nucleus of an atom is called Mass Number.
A, of atom. In situations where it is unnecessary to differentiate between protons and neutrons, these elementary particles are collectively referred to as nucleons. Thus mass number of an atom is equal to the total number of nucleons in the nucleus of atom.
Obviously, the mass number of an atom ⚛️ is a whole number. Since electrons have practically no mass, the mass (or atomic weight) to the nearest whole number.
For examples, the atomic mass of sodium and fluorine obtained by experiment 🧪 is 22.9898 and 18.9984 amu respectively.
Thus their mass numbers are 23 for sodium and 19 for fluorine.
Each different variety of atoms, as determined by the composition of its nucleus, is called a nuclide.
