CHRONOLOGY OF ATOMIC STRUCTURE
1. Dalton(1808) : Discovery of atom
2. Julius Plucker (1859) : First discoverer of cathode rays
3. Goldstein(1886) : Discovered anode rays and proton
4. Sir.J.J.Thomson(1897) : Discovered electron and determined
charge/mass(e/m) ratio for electron
5. Rutherford(1891) : Discovered nucleus and proposed
6. MaxPlanck(1901) : Proposed quantum theory of radiation
7. RobertMillikan(1909) : Determined charge of an electron
8. H.G.J.Mosely(1913) : Discovered atomic number
9. Niels Bohr(1913) : Proposed a new model of atom
10. Clark Maxwell(1921) : Electromagnetic wave theory
11. de-Broglie(1923) : Established wave nature of particles
12. Pauli(1927) : Discovery of neutrino
13. Werner Heisenberg(1927) : Uncertainty Principle
14. James Chadwick(1932) : Discovery of neutron
15. Anderson(1932) : Discovery of positron
16. Fermi(1934) : Discovered antineutrino
17. Hideki Yukawa(1935) : Discovered mesons
18. Segre(1955) : Discovered antiproton
19. Cork and Association(1956) : Discovered antineutron
Progress of Atomic Models
In 1803, John Dalton, proposed his atomic theory. He suggested that atoms were indivisible solid spheres.
J.J.Thomson proposed that an atom was a solid sphere of positively charged material and negatively charged particles, electrons were embedded in it like the seeds in a guava fruit. But later this concept was proved wrong.
Rutherford suggested the planetary model, but this model was rejected.
In 1913, Neils Bohr proposed that electrons revolve around the nucleus in a definite orbit with a particular energy. Based on the facts obtained from spectra of hydrogen atom, he introduced the concept of energy levels of atom.
In 1916 Sommerfeld modified Bohr's model by introducing elliptical orbits for electron path. He defined sub energy levels for every major energy level predicted by Bohr.
The concept of Quantum numbers was introduced to distinguish the orbital on the basis of their size, shape and orientation in space by using principal, azimuthal, magnetic and spin quantum numbers.
From the study of quantum numbers, various rules are put forward for filling of electrons in various orbitals by following
Pauli exclusion principle and
Hunds rule of maximum multiplicity.
In 1921 Burry and Bohr gave a scheme for the arrangement of electrons in an atom. Further the nature of electron (s) is studied.
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