Question

Who modified Bohr’s theory by introducing elliptical orbits for electron path?
A. Rutherford
B. Thomson
C. Sommerfeld
D. Hund

Answer 1

Hint: He is a German physicist whose atomic model allows the explanation of fine – structure of spectral line. He was born on Dec.5 1868 in Russia and died on April 26 1951 in Munich.

Complete answer:
-Bohr’s theory was given by Neil Bohr in 1915 after which the Bohr model of atom was given. The Bohr atomic model explains the movement of electrons in the fixed orbit and not anywhere in between. Neil Bohr also explained that each orbit has its fixed energy level.
-Bohr model failed to explain the effect of magnetic field on the spectra of atoms. It also violated the Heisenberg Uncertainty principle and it was not able to explain the spectra obtained from larger molecules.
-Bohr's theory was further modified by Sommerfeld by introducing elliptical orbits for electron paths. His model explains the fine spectrum of hydrogen atoms.
-The postulates of the Sommerfeld model are shown below.
(1) He said that the orbits can both be circular or elliptical.
(2) When the path of electrons is elliptical, then there are two axes – major axis and minor axis. When the length of major and minor axis becomes equal then the orbit is circular.
(3) The angular momentum of electrons moving in the elliptical orbit is where k is integer number zero.
(4) Sommerfeld suggested the sub energy levels s,p,d,f.
(5) He also explains that when the electrons get excited and jump from one orbital to another, the difference in energy depends on the sub energy level.
(6) He explains the splitting of individual spectral lines of hydrogen.
Thus, Sommerfeld modified Bohr’s theory by introducing elliptical orbits for electron paths.
Therefore, the correct option is C.

Note:
The Sommerfeld model does not explain the Zeeman and Stark effect. He introduced the Azimuthal quantum number (l) which helps to determine the orbital angular quantum number.