The significant break through in chemistry was made during last two centuries wherein we analysed the subject more minutely, even upto the level of the smallest creative and functional unit of substances i.e. atom, which is involved in all sorts of chemistry any how. During this span of time atoms could be fragmented into still finer subatomic constituents and existence of nucleus was confirmed. Some of the legendry chemists could manage to peep inside the atom and gave every detail about the atomic world through their atomic models. Bohr gave the detail profile of orbiting electrons and successfully explained the line spectrum of hydrogen. With the unfolding of the structure of atom the chemical science passed from its infancy state i.e. crude, empirical and macroscopic state to scientific, rational, microscopic and mature state of understanding. Infact, the outlook of every chemistry of a substance is a reflection of ingoing business of extra nuclear electrons. So the idea regarding arrangement of electrons around the nucleus is essential to understand the chemical behaviour on atomic level. This topic will be concluded with the explicit detail about electronic configuration to make the fascinating chemistry lucid and comprehensive.

1. 1. The energy per mol necessary
to ionize a hydrogen atom in the
ground state is :
(a) 1313 kJ/mol (b) 1013 kJ/mol
(c) 2626 kJ/mol (d) 2000 kJ/mol

2. 2. The hydrogen-like ion that has the wavelength
difference between the first lines of Balmer and Lyman
series equal to 59.3 nm (RH = 109678 cm–1) is :
• (a) He+ (b) Li2+
• (c) Be3+ (d) B4+

3. 3. The wavelength of the next line in the series
having lines of spectrum of H-atoms of wavelengths
6565 Å, 4863 Å, 4342 Å and 4103 Å is :
• (a) 4061.47 Å
• (b) 3000 Å
• (c) 2500 Å
• (d) 2000 Å

4. 5. Which of the following transitions have the wave
number ratio as 108 : 7 in atomic spectra of hydrogen?
• (a) First Lyman and first Brackett
• (b) First and second Lyman
• (c) First Lyman and first Balmer
• (d) First Lyman and first Paschen

5. 5. Order of number of revolution/sec
1, 2, 3, 4 for I, II, III and IV orbits is :
• (a) 1 > 2 > 3 > 4
• (b) 4 > 3 > 2 > 1
• (c) 1 > 2 > 4 > 3
• (d) 2 > 3 > 4 > 1

6. 6. The ratio of the difference in energy of electron
between the first and second Bohr’s orbits to that
between second and third Bohr’s orbit of the same
atom is :
• (a) 1/3 (b) 27/5
• (c) 9/4 (d) 4/9
•

7. 7. If the threshold frequency of a metal for
photoelectric effect is 0, then which of the following
will not happen?
(a) If frequency of the incident radiation is 0, the
kinetic energy of the electrons ejected is zero.
(b) If frequency of incident radiation is , the kinetic
energy of the electrons ejected will be h – h 0.
(c) If frequency is kept same at but intensity is
increased, the number of electrons ejected will
increase.
(d) If frequency of incident radiation is further
increased, the number of photo–electrons ejected
will increase.
•

8. 8 The wave number of any spectral line for an electronic
transition in the spectrum is directly proportional to
(a) The velocity of the electrons undergoing
transition.
(b) The number of electrons undergoing
transition.
(c) (n2 – n1) where n2 and n1 represent the
principal quantum numbers of higher and
lower level.
(d)1/n1-1/n2

9. 9. Which of the following sets of
quantum numbers is permissible for
an electron is an atom?
• (a) n = 1, l = 1, m = 0, s = +1/2
• (b) n = 3, l = 1, m = – 2, s = -1/2
• (c) n = 2, l = 1, m = 0, s = +1/2
• (d) n = 2, l = 0, m = 0, s = 1

10. 10. According to Bohr's Model of hydrogen atom
(a) total energy of the electron is quantized
(b) angular momentum of the electron is quantized
and given as 2
·)1(
h
ll
(c) both (a) and (b)
(d) none of these

11. 11 Which of the following statement is correct in relation
to the hydrogen atom?
(a) 3s–orbital is lower in energy than 3p–orbital.
(b) 3p–orbital is lower in energy than 3d–orbital.
(c) 3s and 3p–orbitals are of lower energy than 3d–
orbitals.
(d) 3s, 3p and 3d–orbitals all have same energy.

12. SUBJECTIVE QUESTION FOR AIEEE
1. Suppose 10-17 J of energy is needed by the interior of the human eye to see an
object. How many photons of green light ( = 550 nm) are needed to generate this
minimum amount of energy ?
•
2. Calculate the frequency of the spectral line emitted when the electron in (n = 3) in
hydrogen atom dexcites to ground state. (RH = 2.92 10 sec )
3. Calculate the velocity (cm sec-1) of an electron placed in the third orbit of the
hydrogen atom. Also calculate the number of revolutions per second that this
electron makes around the nucleus.
4. The ionisation energy of hydrogen atom is 13.6 eV. What will be the ionisation
energy of He and Li ions ?

13. 5. Iodine molecule dissociates into atoms after absorbing light
of 4500 A . If one quantum of radiation is absorbed by each
molecule, calculate kinetic energy of iodine atoms. (Bond
energy of I2 = 240 kJ mol)
6. The ionisation energy of He is 19.6 10 J atmo . Calculate
the energy of the first stationary state of Li .
7. An organic compound absorbs light of wavelength 4500 A
and then fluorescence light of wavelength 5400 A . Under
given conditions 50% of absorbed energy is re-emitted out
as fluorescence. Calculate the ratio of quanta emitted out
to the number of quanta absorbed.