what is Bohr's atomic model
Answers
Bohr model or Bohr diagram, presented by Niels Bohrand Ernest Rutherford in 1913, is a system consisting of a small, dense nucleus surrounded by revolving electrons —similar to the structure of the Solar System, but with attraction provided by electrostatic forces rather than gravity. After the cubic model(1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911) came the Rutherford–Bohr model or just Bohr model for short (1913). The improvement to the Rutherford model is mostly a quantum physical interpretation of it. The model's key success lay in explaining the Rydberg formula for the spectral emission lines of atomic hydrogen. While the Rydberg formula had been known experimentally, it did not gain a theoretical underpinning until the Bohr model was introduced. Not only did the Bohr model explain the reason for the structure of the Rydberg formula, it also provided a justification for its empirical results in terms of fundamental physical constants.
The Bohr model is a relatively primitive model of the hydrogen atom, compared to the valence shell atom. As a theory, it can be derived as a first-order approximation of the hydrogen atom using the broader and much more accurate quantum mechanics and thus may be considered to be an obsolete scientific theory. However, because of its simplicity, and its correct results for selected systems (see below for application), the Bohr model is still commonly taught to introduce students to quantum mechanics or energy level diagrams before moving on to the more accurate, but more complex, valence shell atom. A related model was originally proposed by Arthur Erich Haas in 1910 but was rejected. The quantum theory of the period between Planck's discovery of the quantum (1900) and the advent of a full-blown quantum mechanics (1925) is often referred to as the old quantum theory
■Bohr:
accepted Rutherford’s nucleus model of atom and Planck’s quantum theory.
proposed an atomic model to explain the spectra emitted by hydrogen atoms.
Called planetary model of the atom.
Based on four postulates.
■Postulates:
●NUCLEAR CONCEPT:
An atom consists of small and massive central core, called as the nucleus, around which planetary electrons revolve. The centripetal force required for their revolution around the atom’s nucleus is provided by the electrostatic force of attraction between the nucleus and the electron.
◆QUANTUM CONDITION:
Of all the possible circular orbits allowed by the classical theory, the electrons are allowed to revolve only in those orbits in which, the angular momentum of the electron is an integral multiple of h/2pi. This is Bohr’s famous quantum condition.
mvr =nh/2pi
●STATIONARY ORBITS:
An electron does not radiate energy, while revolving in a permissible orbits. These permissible, non - radiating orbits are called as stationary orbits.
●FREQUENCY CONDITION:
An electron can absorb or emit radiation in the form of discrete energy photons only when it jumps from a lower energy orbit to a higher energy orbit or from a higher energy orbit to a lower energy orbit, respectively. This is Bohr’s famous frequency condition.
