A hypothetical atom has atomic number 71. Using the Bohr hypothesis, find the frequency of revolution for the electron in the 18th energy level, in Hz.
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According to the Bohr hypothesis
1
The centripetal force on the electron in an orbit is equal to the Coulomb force between nucleus and electron. Thus
Where m = mass of the electron, e = magnitude of the charge on the electron, Z = atomic number of the atom,
r = distance between electron and nucleus, v = Speed of the electron in an orbit, k = Coulomb's constant
2
The orbit angular momentum of the revolving electron in an orbit is quantized. Thus
Where n = 1, 2, 3 ........ and 
= Reduced planck constant
The atomic number of an atom is Z = 71
Using Bohr hypothesis
............................(1)
Now
Using equation (1)
Where
= Bohr radius = 0.529 × 10- 10 m
Using equation (1)
The frequency of revolution of the electron is given by
For 18th energy level n = 18
m = 9.11 × 10- 31 kg
= 1.05457 × 10- 34 J.s
Thus
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