The document summarizes different atomic models including Thomson's model, Bohr's model, Sommerfeld's model, and the vector atom model. Thomson's model proposed that atoms are made up of positive charges and distributed negative charges. Bohr's model introduced allowed orbits and quantized angular momentum. Sommerfeld's model accounted for elliptical orbits and relativistic effects. The vector atom model explained phenomena like the Zeeman and Stark effects using quantum numbers for orbital and spin angular momentum.

1. A Seminar on
DIFFERENT ATOMIC MODELS
Presented by:
SHANTI SHARMA
4TH SEMESTER

2. CONTENTS
 Thomson’s Atomic Model
 Drawbacks of Thomson’s Atomic Model
 Bohr atom model
 Drawbacks of Bohr atom model
 Sommerfeld’s atom model
 Sommerfeld’s relativistic atomic model
 Drawbacks of Sommerfeld’s atom model
 The vector atom model
 Conclusion
 References

3. Thomson’s Atomic Model
J. J. Thomson
1. Electron enter into the constitution of all atoms
2. Since the atom as a whole is electrically neutral the
quantity of positive and negative charge in it must be the
same.

4. Drawbacks
He explained that hydrogen can give rise only
to a single spectral lines.
He couldn't explain the fine spectra

5. BOHR ATOM MODEL
He proposed the following postulates-
(1)An electron cannot revolve round the
nucleus in all possible orbit. It can revolve
round the nucleus in those allowed orbits
for which the angular momentum of the
electron is an integral multiple of h .
2
Niels Bohr
Bohr’s atomic
model

6. (2)An atom radiates energy only
when electron jumps from a
stationary orbit of higher energy to
one of lower energy. If electron
jumps from an initial orbit of
energy E i to the final orbit of
energy E f ( E i E f ) ,a photon of
Ei E f
frequency is emitted.
h

7. The Bohr formulae
-e
+Ze r
Radius of the nth permissible orbit for
hydrogen 2 2
n h 0
rn 2
e m
The total energy of the electron in the nth orbit
4 2
me Z
En 2 2 2
8 0n h

8. Lyman
n=1 Balmer
n=2
n=3 Paschen
Pfund
n=4
n=5
n=7 n=6
Brackett
Different spectral series of hydrogen atom according to Bohr.

9. The energy level diagram
4 2
The equation me Z Can be diagrammatically
En 2 2 2
8 0n h
represented. Then it is called The energy level
diagram.
n
---------------------------------------------------- En (eV )
n=6
n=5
Pfund
n=4
-085
Brackett
n=3 -1.5
Paschen
Balmer
n=2 -3.4
H H H
n=1
Lyman -13-6

10. Drawbacks
Spectrograph of high resolving showed that lines
are not single. Each spectral lines actually
consisted of several very close line packed
together. This is called fine structure of spectral
lines. Bohr theory could not explain this fine
structure.
Sommerfeld’s atom model
Sommerfeld introduced two main modification in
Bohr’s model:
(1)The path of an electron around the nucleus, in
general ,is an ellipse with the nucleus at one of the
foci.

11. (2)The velocity of the electron moving in an
elliptical orbit varies considerably at different parts
of the orbit.
electron
r
N
Elliptical orbit for hydrogen atom

12. The condition that determines the allowed elliptical orbit is
b n
a n
Whenn n, b a , 0 and the orbit become circular
 n 0
 n n
n has n different values

13. n 2, n 1
n 1, n 1 n 3, n 1
n 2, n 2 n 3, n 2
n 3, n 3
TOTAL ENERGY
4 2
me Z
En 2 2 2
8 0n h

14. Sommerfeld’s relativistic atomic model
1
The velocity of electron in the elliptic orbits is C
137
So Sommerfeld taking into account the variation of mass
with velocity.
He showed that the relativistic equation describing the
path of the electron is
1 1 cos
(1)
r a(1 2 )
2 z 2e 4
1
16 2 0 p 2c 2
2

15. The path of the electron given by equation(1) is an
ellipse whose major axis precesses slowly in the plane
of the ellipse about an axis through the nucleus.
The total energy in the relativistic theory
4 2 4 4 2
me Z me Z n 3 1
En 2 2 2 2 2
( ) 4
8 0n h 8 0h n 4 n
e2 1
2 0 ch 137
is called the fine structure constant

16. Fine structure of the H lines
H Line is due to the transition from n=3
state to n=2 state of hydrogen atom.
33
32
31
22
21

17. Drawbacks
Sommerfeld’s theory was able to give an
explanation of the fine structure of the spectral
line of hydrogen atom. But he could not predict
the correct of spectral lines.

18. The vector atom model
The two distinct features of vector atom
model are:
The conception of spatial
quantization
The spinning electron hypothesis

19. Quantum no. associated with the
Vector Atom Model
• A total quantum number n, it can take only
integral values 1,2,3..etc
• An orbital quantum number l, which may take any
integral value between 0 and (n-1) inclusively.
• A spin quantum number s, the magnitude of
which is always ½.
• A total angular quantum number j, the resultant
angular momentum of the electron due to both
orbital and spin motions i.e vector sum of l and s.

20. Vector atom Model for Orbital
Angular Momentum
The orbital angular momentum The diagram shows that the possible
for an atomic electron can be values for the "magnetic quantum
visualized in terms of a vector number" ml for l=2 can take the values
model where the angular ml =-2,-1,0,1,2
momentum vector is seen as or, in general,
precessing about a direction in ml=-l,-l+1,……..,l-1,l
space.

21. Vector atom Model for Total Angular
Momentum
When orbital angular momentum L and electron spin angular momentum S
are combined to produce the total angular momentum of an atomic
electron, the combination process can be visualized in terms of a vector
model.

22. Conclusio
n
Vector atom model can explain Zeeman
effect, Stark effect.
It can also explain the complex spectra of
alkali metal like sodium.
And also can explain how the orbital
electrons in an atom are distributed
around the nucleus.

23. References
• ATOMIC PHYSICS
- J.B. RAJAM
• INTRODUCTION TO ATOMIC SPECTRA
-HARVEY ELLIOTT WHITE
• http://www.tutornext.com/lesson/vector-atom-
model/1243900
• http://www.chembio.uoguelph.ca/preuss/1_5_V
ectorModel.pdf

24. THANK
YOU