Chapter 2 – Structure of Atom
Assignment 5
Q.1. Calculate the radius of Bohr's fifth orbit for hydrogen atom.
[ Ans: 1.3225 nm ]
Q.2. Calculate the energy associated with the first orbit of He+. What is the radius of this orbit?
[ Ans: – 8.72 × 10–18 J, 0.02645 nm ]
Q.3. Calculate the wave number for the longest wavelength transition in the Balmer series of atomic hydrogen.
[ Ans: 1.523 × 106 m–1 ]
Q.4. The electronic energy in hydrogen atom is given as 
J.
Calculate the energy required to remove an electron completely from n = 2 orbit. What is the longest wavelength of light in cm that can be used to cause this transition ?
[ Ans: 3647 Å ]
Q.5. What are the frequency and wavelength of a photon emitted during a transition from n = 5 to n = 2 state in the hydrogen atom?
[ Ans: 6.91 × 1014 s–1, 434 nm ]
Q.6. According to Bohr's theory, the electronic energy of hydrogen atom in the nth Bohr orbit is given by
J per atom
Calculate the longest wavelength of light that will be needed to remove an electron from the third orbit of He+ ion.
[ Ans: 205.5 nm ]
Q.7. The radius of first Bohr orbit of hydrogen atom is 0.529 Å. Calculate the radius of
(i) the third orbit of He+ ion
(ii) the second orbit of Li2+ ion.
[ Ans: (i) 2.384 Å (ii) 0.7053 Å ]
Q.8. Calculate the ratio of the radii of 2nd and 3rd orbits of H-atom.
[ Ans: 4 : 9 ]
Q.9. Light of wavelength 1281.8 nm is emitted when an electron of H-atom drops from 5th to 3rd energy level. Calculate the wavelength of the photon emitted when electron falls from third to ground level.
[ Ans: 102.5 nm ]
Q.10. The electronic energy of H atom is 
J / mol.
Calculate
(i) First excitation energy of the electron in the hydrogen atom.
(ii) Ionization energy of the hydrogen atom.
[ Ans: (i) 9.84 × 105 J mol–1 (ii) 1.312 × 106 J mol–1 ]
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