1. ChaPtER 5:
Spectral Lines Of Hydrogen

2. SCOPE OF STUDY
SUB TOPICS
Energy
Emitted and
Absorbed In A
transition
Electronic
Transition in
Hydrogen Atom
Lyman Series,
Balmer Series
and Paschen
Series

3. ELECTRONIC TRANSITION IN
HYDROGEN ATOM
DEFINITION
Molecular electronic transitions take place
when valence electrons in a molecule are
excited from one energy level to a higher
energy level.

4. ELECTRONIC TRANSITION IN
HYDROGEN ATOM
Example Of Electronic Configuration in Metals
scandium
Sc
[Ar] 3d1 4s2
titanium
Ti
[Ar] 3d2 4s2
vanadium
V
[Ar] 3d3 4s2
chromium
Cr
[Ar] 3d5 4s1
manganese
Mn
[Ar] 3d5 4s2
iron
Fe
[Ar] 3d6 4s2
cobalt
Co
[Ar] 3d7 4s2
nickel
Ni
[Ar] 3d8 4s2
copper
Cu
[Ar] 3d10 4s1
zinc
Zn
[Ar] 3d10 4s2

5. ELECTRONIC TRANSITION IN
HYDROGEN ATOM
In 1913, it was Neils Bohr who solved many of the problems at the time by
proposing that the electron revolves around the nucleus of the atom with a
definite fixed energy in a fixed path, without emitting or absorbing energy.
The electron in the hydrogen atom exists only in certain definite energy
levels.
These energy levels are called Principal Quantum Levels, denoted by the
Principal Quantum Number, n. Principal Quantum Level n = 1 is closest to the
nucleus of the atom and of lowest energy.

6. ELECTRONIC TRANSITION IN
HYDROGEN ATOM
When the electron occupies the energy level of lowest energy the atom is
said to be in its ground state.
An atom can have only one ground state.
If the electron occupies one of the higher energy levels then the atom is in
an excited state.
An atom has many excited states.

7. ENERGY EMITTED AND ABSORBED
IN A TRANSITION
When a gaseous hydrogen atom in its ground state is excited by an input of
energy, its electron is 'promoted' from the lowest energy level to one of higher
energy.
The atom does not remain excited but re-emits energy as electromagnetic
radiation.
This is as a result of an electron 'falling' from a higher energy level to one of
lower energy.
This electron transition results in the release of a photon from the atom of an
amount of energy (E = hn) equal to the difference in energy of the electronic
energy levels involved in the transition.

8. ENERGY EMITTED AND ABSORBED
IN A TRANSITION
In a sample of gaseous hydrogen where there are many trillions of atoms all
of the possible electron transitions from higher to lower energy levels will take
place many times.
A prism can now be used to separate the emitted electromagnetic radiation
into its component frequencies (wavelengths or energies).
These are then represented as spectral lines along an increasing frequency
scale to form an atomic emission spectrum.

9. ENERGY EMITTED AND ABSORBED
IN A TRANSITION
A hydrogen atom in its Ground State.
The electron occupies the lowest
possible energy level which in the
case of hydrogen is the Principal
Quantum Level n = 1.

10. ENERGY EMITTED AND ABSORBED
IN A TRANSITION
The Bohr theory was a marvellous success in explaining the spectrum of the
hydrogen atom.
His calculated wavelengths agreed perfectly with the experimentally measured
wavelengths of the spectral lines.
More recent theories about the electronic structure of atoms have refined these ideas,
but Bohr's 'model' is still very helpful to us.
For clarity, it is normal to consider electron transitions from higher energy levels to
the same Principal Quantum Level.
The diagram below illustrates the formation of a series of spectral lines in the visible
region of the spectrum of electromagnetic radiation for hydrogen, called the Balmer
Series.

11. ENERGY EMITTED AND ABSORBED
IN A TRANSITION

12. ENERGY EMITTED AND ABSORBED
IN A TRANSITION
The Bohr model for an electron transition in hydrogen
between quantized energy levels with different quantum numbers n
yields
a
photon
by
emission
with
quantum
energy:

13. ENERGY EMITTED AND ABSORBED
IN A TRANSITION
This is often expressed in terms of the inverse wavelength or "wave
number" as follows:

14. Hydrogen Spectrum

15. LYMAN SERIES, BALMER SERIES &
PASCHEN SERIES
As referred to above for hydrogen atoms, electron transitions form higher energy
levels all to the n = 2 level produce a series of lines in the visible region of the
electromagnetic spectrum, called the Balmer Series.
The series of lines in the ultra-violet region, called the Lyman Series, are due to
electron transitions from higher energy levels all to the n = 1 level, and these were
discovered after Bohr predicted their existence.

16. LYMAN SERIES, BALMER SERIES &
PASCHEN SERIES
Within each series, the spectral lines get closer together with increasing
frequency.
This suggests that the electronic energy levels get closer the more distant they
become from the nucleus of the atom.
No two elements have the same atomic emission spectrum; the atomic emission
spectrum of an element is like a fingerprint.
Energy-level diagram below for the hydrogen atom, showing the transitions for
the spectral lines of the Lyman, Balmer, and Paschen series. Each vertical arrow
represents an atomic transition that gives rise to the photons of one spectral line (a
single wavelength or frequency).

17. LYMAN SERIES, BALMER SERIES & PASCHEN
SERIES

18. LYMAN SERIES, BALMER SERIES &
PASCHEN SERIES

19. LYMAN SERIES, BALMER SERIES &
PASCHEN SERIES
The measured lines of the Balmer series of hydrogen in the nominal visible region
are:
Wavelength
(nm)
Relative
Intensity
Transition
Color
383.5384
5
9 -> 2
Violet
388.9049
6
8 -> 2
Violet
397.0072
8
7 -> 2
Violet
410.174
15
6 -> 2
Violet
434.047
30
5 -> 2
Violet
486.133
80
4 -> 2
Bluegreen (cyan)
656.272
120
3 -> 2
Red
656.2852
180
3 -> 2
Red

20. LYMAN SERIES, BALMER SERIES &
PASCHEN SERIES
Example : Wavelength of a Lyman line.
Use this figure to determine the wavelength of the first
Lyman line, the transition from n = 2 to n = 1. In what
region of the electromagnetic spectrum does this lie?
Solution:
The energy is the difference between the two
levels, 10.2 eV. Then λ = hc/E = 1.22 x 10-7 m.
This is an ultraviolet photon.

21. LYMAN SERIES, BALMER SERIES &
PASCHEN SERIES
Example : Wavelength of a Balmer line.
Determine the wavelength of light emitted when a hydrogen atom makes a
transition from the n = 6 to the n = 2 energy level according to the Bohr
model.
Solution:
Using equation, we find λ = 4.10 x 10-7 nm (violet).

22. THE END …..
“if A is success in
life, then A=x+y+z;
Work = x;
y = play; and z =
keeping your mouth