Quantum chemistry is the application of quantum mechanics to chemical systems. It began with Max Planck's explanation of blackbody radiation using discrete energy levels, and contributions from Einstein, Bohr, de Broglie, Heisenberg, Schrodinger and others who developed quantum theory. Quantum mechanics was able to successfully model atomic and molecular behavior that classical mechanics could not explain. It remains an important tool for understanding molecular properties and reactions using powerful computers.

1. EVOLUTION
OF QUANTUM
CHEMISTRY
PRIYANKA AHIRWAR
19CHY212

2. CONTENTS
What is QUANTUM CHEMISTRY?
 MAJOR HISTORICAL CONTRIBUTORS
Why classical mechanics failed?
Birth of Quantum mechanics
Evolution-A new phase
Conclusion

3. WHAT IS QUANTUM CHEMISTRY?
Quantum chemistry is a branch of chemistry focused on the
application of quantum mechanics in physical models and
experiments of chemical systems.
The rapid development of computer technologies has greatly
encouraged chemists to use quantum chemistry to
understand, model, and predict molecular properties and
their reactions, properties of nano materials, and reactions .
Quantum chemistry is a very powerful tool to study the
properties of molecules and their reactions.

4. HISTORICAL CONTRIBUTORS
‘Quantum mechanics’ history, as it twist with the history
of quantum chemistry, began essentially with a number of
different scientific discoveries.
There were many scientists who contributed to the origin of
Quantum Chemistry which had vital development.

5. THOMAS YOUNG-(1801)

6. MICHAEL FARADAY-1838

7. Kirchhoff had defined a blackbody as an object that
re-emits all of the radiant energy incident upon it;
i.e., it is a perfect emitter and absorber of radiation.
There was, therefore, something absolute
about blackbody radiation.
GUSTAV KIRCHHOFF (1859-60)

8. HEINRICH HERTZ-(1887)
Discovery of Photoelectric Effect

9. HERTZ PREDICTION
 Number of ejected electrons depend
upon intensity
 Energy of ejected electrons depends on
the intensity
 No obvious dependence of frequency.

10. JOHANNES RYDBERG-(1888)

11. J.J.THOMSON-(1897)
 Discovery of electron

12. CLASSICAL MECHANICS
 Classical mechanics deals with the movement of
macroscopic particles at speed of around 105-106
 CLASSICAL MECHANICS IS BASED UPON THE NEWTON
LAWS AND CLASSICAL THEORIES:
For example: we study the motion of planets, projectile
motion and motion macroscopic particles using the laws of
classical mechanism.
PROJECTILE MOTION

13. BLACK BODY RADIATION
An object that absorbs
all radiation falling on it, at all
wavelengths, is called a black
body

14. RAYLEIGH-JEANS LAW (1894)
 Lord Rayleigh and J. H. Jeans developed an equation which
explained blackbody radiation at low frequencies.
 Classical physics assumed that energy emitted by atomic oscillations
could have any continuous value.
 The equation which seemed to express blackbody radiation was built
upon all the known assumptions of physics at the time.
𝒅𝒑 𝒗, 𝑻 = 𝝆 𝒗(T)𝒅𝒗 = 𝟖𝝅𝒌 𝑩𝑻
𝒄 𝟑 𝒗 𝟐 𝒅𝒗

15. ULTRA VIOLET CATASTROPHE
 At high frequencies, however, the Rayleigh- Jeans law predicts that the
radiant energy density diverges as v2 . Because the frequency increases as
the radiation enters the ultraviolet region, this divergence was termed the
ultraviolet catastrophe
.

16. WHY CLASSICAL MECHANICS FAILED?
Classical mechanics could not explain the black body radiation properly
There was no explanation of Photoelectric effect in Classical Mechanics
It was only able to explain speed of particles less than the speed of light.
This theory was not able to explain the stability of an atom

17. BIRTH OF QUANTUM MECHANICS
 It was the failure of Classical mechanics which gave birth to
‘QUANTUM THEORY’.
 The first person to offer a successful explanation of blackbody
radiation was the German physicist Max Planck in 1900.
 He made the revolutionary assumption that the energies of the
oscillators were discrete and had to be proportional to an integral
multiple of the frequency or, in equation form, that E = nh 𝑣, where E is
the energy of an oscillator, n is an integer, h is a proportionality
constant or Planck's constant, and v is the frequency.
 Planck assumed that the radiation emitted by the blackbody was
caused by the oscillations of the electrons in the constituent particles
of the material body.

18. CLASSICAL MECHANICS DID NOT EXPLAIN
 Number of electrons depend upon intensity
 Energy of electrons does not depend on intensity
 Cut off frequency :minimum frequency is required
to get any emission
 Above cut off frequency, energy increases linearly
with frequency.

19. PHOTOELECTRIC EFFECT ALBERT EINSTIEN-(1905)
Einstein proposed that light behaved like a stream of photons with an energy
E=h 𝑣.
𝐸 = ℎ𝑓 = ℎ
𝑐
λ
Energy of emitted electron
𝐸 = ℎ𝑓 − ∅
Some minimum energy to remove electron is known as “WORK FUNCTION”.

20. NIELS BOHR-(1913)

21. DE BROGLIE HYPOTHESIS-(1924)
Louis de-Broglie suggested that similar to light dual nature "every
moving matter has a associated wave“
The wave associated with particle is called as matter wave or de
Broglie wave.
The above relation is known as de-Broglie equation and the
wavelength λ is known as de-Broglie wavelength.
λ =
ℎ
𝑚𝑣

22. EVOLUTION- A NEW PHASE
Start of 1920’s is marked as a stage when Quantum mechanics had
reached a next level.
The term ‘QUANTUM MECHANICS’ was coined by Werner
Heisenberg, Max Born and Wolfgang Pauli in early 1920’s
A Phase when ‘QUANTUM FIELD THEORY’ EMERGED

23. HEISENBERG’S UNCERTAINITY PRINCIPLE-(1925)
∆𝑥∆𝑝 ≥ ℎ

24. SCHRODINGER’S WAVE EQUATION-(1926)
The Schrödinger equation (also known as Schrödinger’s wave
equation) is a partial differential equation that describes the
dynamics of quantum mechanical systems via the wave function.
The trajectory, the positioning, and the energy of these systems
can be retrieved by solving the Schrödinger equation.
All of the information for a subatomic particle is encoded within a wave
function. The wave function will satisfy and can be solved by using the
Schrodinger equation.
TIME DEPENDENT EQUATION
HΨ(x,t) = 𝑖ℏ
𝜕𝛹
𝜕𝑡
TIME INDEPENDENT EQUATION
ℎ2
2𝑚
𝑑2
ψ(𝑥)
𝑑𝑥2 + (E − v(x))ψ(x)=0

25. COINED BLACK
BODY
RADIATION
INTRO TO
PHOTOELECTRIC
EFFECT
FLOWCHART-HISTORICAL DEVELOPMENT
CATHODE RAY
TUBE
RYDBERG
EQUATION
THOMAS YOUNG MICHAEL FARADAY
RUTHERFORD’S
ATOMIC MODEL
PAULI’S
EXCLUSION
PRINCIPLE
DE BROGLIE
HYPOTHESIS
SCHRODINGER’S
WAVE
FUNCTION
BOHR’S ATOMIC
MODEL
PHOTOELECTRIC
EFFECT
PLANCK’S
CONSTANT
RAYLEIGH-
JEAN’S LAW ON
BLACK BODY
RADIATION
HEISENBERG’S
UNCERTAINITY
PRINCIPLE
STATISTICAL
PREDICTION OF
VARIABLES
SHAPING OF
QUANTUM
FIELD THEORY
DIRAC WAVE
EQUATION
GUSTAV KIRCHHOFF
CATHODE RAY
EXPT
DOUBLE SLIT
EXPT
HEINRICH HERTZ JOHANNES RYDBERG
ERNST RUTHERFORDALBERT EINSTEINMAX PLANCKLORD RAYLEIGH NEILS BOHR LOUIS DE BROGLIE
WERNER HEISENBERGWOLFGANG PAULI MAX BORN PASCAL JORDAN ERWIN SCRODINGER PAUL DIRAC
JJ THOMSON

26. APPLICATION
CESIUM CLOCK
The cesium clock is the most accurate type of clock yet developed. This
device makes use of transitions between the spin states of the cesium
nucleus and produces a frequency which is so regular that it has been
adopted for establishing the time standard.

27. CONCLUSION
• .
 These scientists had contributed in many ways for the development
of Quantum Chemistry.
 Which is the fundamental part of the modern science without their
contribution ,evolution wouldn't have been happened.
 Their would have been a void in development of science today but
Quantum Chemistry is regarded as one of the most important
aspects of modern science.
 which is used in modern physics ,cosmology, chemistry and many
other fi.

28. REFERENCES
 Jadish Mehran and Helmut Rechenberg, The Historical Development of
Quantum Theory, Springer-Verlag, New York, 1982.
 Max Jammer, The Conceptual Development of Quantum Mechanics, McGraw
Hill, USA, 1966.
 Max Planck and Morton Masius , The Theory of Heat Radiation,1914.
 Measurement Science and Technology
 Caesium atomic clocks: function, performance and applications
 Andreas Bauch,Published 16 July 2003 Measurement Science and
Technology, Volume 14, Number 8

29. THANK YOU!