1) When hydrogen gas is excited by electricity, the electrons absorb energy and move to higher energy orbits. As the electrons fall back down, they emit photons of light at specific wavelengths. 2) The wavelengths of emitted photons form distinct line spectra that are unique to hydrogen. Bohr calculated the wavelengths for the hydrogen spectral lines. 3) There are several hydrogen spectral series defined by the electron falling from different excited states to the n=1, 2, 3, 4, or 5 states. The Lyman, Balmer, Paschen, Brackett, and Pfund series occur in the ultraviolet, visible, and infrared regions of the spectrum.

1. Hydrogen Spectrum
Chapter # 2
ATOMIC STRUCTURE
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2. Spectrum
White light is made up of all
the colors of the visible
spectrum.
Passing it through a
prism separates it.
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3. If the Light is not white
By heating a gas or with
electricity we can get it to
give off colors.
Passing this light through a
prism does something
different.
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4. Hydrogen
Gas
Prism
White Light
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5. Atomic Spectrum – Finger
Prints of an Atom
Each element gives
off its own
characteristic
colors.
Can be used to
identify the atom.
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6. Atomic Spectrum – Finger
Prints of an Atom
These are called
line emission
spectra
The light is emitted
given off
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7. Hydrogen Spectral Lines
Bohr calculated the energy, frequency and wave
number of the spectral emission lines for
hydrogen atom.
The wave number of different spectral lines can
be calculated corresponding the values of n1
and n2.
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8. Bohr’s Explanation for
Hydrogen Spectrum
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When current is passed through Hydrogen gas in
the discharge tube at low pressure, the
molecules of Hydrogen break in to atoms.
These atoms absorbs energy from electric spark.
Electrical Discharge
H2
(gas)
2 H
(atoms)Low Pressure

9. e
Ground State
(Low Energy)
Excited State
(High Energy)
Energy In
The electrons of
Hydrogen atoms are
excited to high energy
levels.
The higher energy
orbits to which electron
migrate depend upon
the amount of energy
absorbed by the
electron.
e
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10. e
Ground State
(Low Energy)
Excited State
(High Energy)
Photon
out
These excited electrons
being unstable come back
to one of the lower energy
level.
The electron may come to
the lowest energy levels.
In this way they emit
energy they had absorbed.
Photon
out
e
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11. Prepared By: Sidra Javed

12. Wave number of spectral
lines
Different spectral series are produced
depending upon the excited and ground
energy level of electron.
Wave number of these spectral lines can be
calculated by Bohr’s equation.
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13. Prepared By: Sidra Javed

14. Lymen Series
The spectral lines in Lymen Series are explained
by considering that the electron falls back to
n=1 from higher levels
,...4,3,2
where,
1
1
1
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2
2
2
2
7

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
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




n
n

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15. Lymen Series
(Ultra-violet Region)
n=7
n=5
n=6
n=4
n=3
n=2
n=1
n=∞
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nn


16. Balmer Series
In this series the electrons falls back to n=2
,...6,5,4,3
where,
1
2
1
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2
2
2
2
7








n
n

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17. Balmer Series
(Visible Region)
n=7
n=5
n=6
n=4
n=3
n=2
n=1
n=∞
Hα
Hβ
Hγ
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 
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m
nn


18. Paschen Series
In this series the electrons falls back to n=3
,...7,6,5,4
where,
1
3
1
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2
2
2
2
7








n
n

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19. Paschen Series
(Infra Red Region)
n=7
n=5
n=6
n=4
n=3
n=2
n=1
n=∞
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nn
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20. Brackett Series
In this series the electrons falls back to n=4
,...7,6,5
where,
1
4
1
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2
2
2
2
7








n
n

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21. Brackett Series
n=7
n=5
n=6
n=4
n=3
n=2
n=1
n=∞
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nn
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22. Pfund Series
In this series the electrons falls back to n=5
,...7,6
where,
1
5
1
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2
2
2
2
7








n
n

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23. Pfund Series
n=7
n=5
n=6
n=4
n=3
n=2
n=1
n=∞
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nn
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24. Prepared By: Sidra Javed

25. The End
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