The document discusses several models of atomic structure: 1. Bohr's model, which postulated that electrons orbit the nucleus in allowed orbits with angular momentum that is an integer multiple of Planck's constant. This model could calculate orbital radii and energies. 2. Sommerfeld's relativistic model improved on Bohr by allowing elliptical orbits and accounting for relativistic effects on electron mass. 3. The vector model introduced spatial quantization and the spinning electron hypothesis to explain phenomena like the Zeeman and Stark effects. It associated quantum numbers with angular momentum. 4. Pauli's exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers.

1. Dr.(Mrs).M.Sankareswari
Assistant Professor of Physics (SF)
V.V.Vanniaperumal College For Women
(Autonomous)
Virudhunagar
1
Structure of the atom

2. “An electron cannot revolve around the nucleus in all
possible orbits” - Classical theory
Bohr’s postulates
1.The electron can revolve around the nucleus
only in allowed or permissible orbits for which the
angular momentum is the integral multiple of h.
2.An atom radiates energy when an electron
jumps from a stationary orbit of higher energy to one
of the orbit of lower energy with the emission of
photon.

3. By using Bohr formulae we can calculate
a) radii of the stationary orbits
b) total energy of the electron in the orbit
Spectral series of the Hydrogen atom
a) Lyman series
b) Balmer series
c) Paschen series
d) Brackett series
e) Pfund series

4. Critical Potentials:
The least energy expressed in electron volts
required to excite a free neutral atom from its ground
state to a higher state.
Excitation Potentials:
The energy in electron volts required to
raise an atom from its normal state into an excited
state.
Ionisation Potentials:
The energy required to remove an electron
from a given orbit to an infinite distance from the
nucleus.

5. Experimental determination of critical
potentials
1. Frank and Hertz’s method
2. Davis and Goucher’s method

6. Sommerfeld’s relativistic atom model
Sommerfeld introduced two main modifications in the Bohr’s theory:
1) The path of the electron around the nucleus in general is
an ellipse with the nucleus at one of the foci. The circular orbits of
Bohr are a special case of this .
2) The velocity of the electron moving in an elliptical orbit
varies considerably at different parts of the orbit. This causes
relativistic variation in the mass of the moving electron.

7. Inadequacies of Bohr atom model
1) Bohr’s theory was able to explain the series of the simplest hydrogen
atom.
2) The older theories were inadequate to explain new discoveries like the
Zeeman effect and Stark effect in which the spectral lines split under
the influence of magnetic and electric fields.
3) Another drawback of the Bohr model was that it could not explain
how the electrons in an atom were distributed around the nucleus.

8. Vector atom model
1) The conception of the spatial quantisation
2) The spinning electron hypothesis

9. Quantum numbers associated with the
vector atom model
• Principal quantum number
• Orbital quantum number
• Spin quantum number
• Total angular quantum number
• Magnetic orbital quantum number
• Magnetic spin quantum number
• Magnetic total angular momentum quantum number

10. Coupling schemes
1) L-S coupling
In this type all the orbital angular momentum of the
vectors combine to form a resultant L, all their spin angular
momentum vectors combine to form a resultant S.
2) j-j coupling
It is employed with the interactions between spin and
orbital vectors of the each electron.

11. Pauli’s exclusion principle
“No two electrons in an isolated atom may have the same
four quantum numbers”

12. Periodic classification of elements
The periodic table is an arrangement of different
elements that exist the nature, based on their chemical
properties and the atomic number. There are 7 periods
and 8 groups in a periodic table.

13. Thank you