Download - Lecture1(Quantm Chem) Ks
Chemistry I (CHEM C141)
K. Sumithra
Chemistry-I (CHEM C141)The Scope and Objective
•The electronic structure of atoms and molecules
•Chemical bonding
•Molecular Spectroscopy
•Phase and chemical equilibrium
•Chemical kinetics.
CHEM C141 Chemistry I•Quantum theory
•Atomic structure and spectra
•Chemical bonding
•Spectroscopy of various types
CHEM C141 Chemistry I•Thermodynamics and thermochemistry
•Statistical thermodynamics
•Phase equilibria
•Mixtures
CHEM C141 Chemistry I•Chemical reaction thermodynamics
•Chemical Kinetics
Main Text:
‘The Elements of Physical Chemistry’, P.W. Atkins & Julio de Paula, Fifth edition (Oxford University Press, Oxford 2009).
Reference :
(i) ‘Physical Chemistry’, G. M. Barrow, Fifth Edition, Special Indian Edition (Tata McGraw Hill Publishing Company Limited, New Delhi 2007).
(ii) ‘Physical Chemistry’, D. W. Ball, First Edition, Indian Edition (Thomson, 2007).
Component Duration Wt % Date/Time
dd/mm/yy
Remarks
Test I 50
min
20% 4.9.2010 Closed book
Test II 50
min
20% 9.10.2010 Open book
Test III 50 min 20% 20.11.2010 Closed book
Comprehensive
examination
3 hrs 40%
16%
Quiz
3.12.2010 -do-
24% -do-
Tutorial Hour
•A review of the lectures •Discussion and interactions•Clarification of doubts •Problem solving
Origin of Quantum Mechanics
Physics in the late 19th Century1.Classical mechanics
Newton’s law applies universally
Any motion arbitrary energy2.The world is deterministic.3.Light is an electromagnetic waveWaves and particles : Distinct concepts
Invalid Assumptions of Classical Physics
1. Any type of motion can be excited to a state of arbitrary energy: Oscillation of a pendulum
Invalid Assumptions of Classical Physics
2. Particle travels in a trajectory or path, with a precise position and momentum at each instant.
Invalid Assumptions of Classical Physics
3. ‘Waves’ and ‘Particles’ are distinct concepts.
These are excellent assumptions at the macroscopic level, but break down when one considers the microscopic level:
Behaviour of very small entities such as electrons, atoms, molecules, etc.
• Need to understand detailed structure of atoms and molecules
Timeline:•Dalton : Concept of atoms (1803)•Avogadro: Concept of molecules (1811)•Thomson: Concept of electron (1897)
Experiments that defied Classical Physics
Black body radiation
Photoelectric effect
Line spectra of atoms
Heat capacity of solids
Interference
Diffraction
Conclusion
Newton’s laws do not apply to
the microscopic world!
Classical mechanics fails
Outcome New Rules
QUANTUM MECHANICS!-a new philosophy
R. P. Feynman : Quantum Mechanics deals with “Nature as she is – absurd”
Stephan Hawking : Quantum mechanics is the basis of modern developments in chemistry, Molecular biology, and electronics, and the foundation for the technology that has transformed the world in the last fifty years
Quantum Mechanics deals with “Nature as she is – amazing!”
"And anyone who thinks they cantalk about quantum theory withoutfeeling dizzy hasn't yet understoodthe first thing about it."
Niels Bohr.
Quantum Mechanics
•Describes rules that apply to electrons in atoms and molecules •Non-deterministic, Probabilistic
-Explains unsolved problems of the late 19th Century-Explains bonding, Structure and reactivity in Chemistry
Electromagnetic spectrum
Much of a person's energy is radiated away in the form of infrared energy.
Thermal RadiationBlackbody Radiation
Blackbody radiation
T
Common observation with heated bodies; Red blue
Black body radiation•Any dense object can radiate energy-
•Graphite 96% Absorption/Emission
•Surface coated with lamp black/ Platinum black
Properties of a perfect blackbody
A blackbody is a perfect absorber or emitter of radiation
The distribution of absorbed or emitted radiation depends only on the absolute temperature, not on blackbody material
Black body radiation
•Perfect black body
•Pin hole in a container Fery
Black body radiation
Problem: To account for the spectral distribution of the power emitted by a black body
Intensity
Wavelength
Radiates at all wavelengths in principle! Curve touches X axis at infinity
Major experimental observations
Not all wavelengths of light are emitted equally
At any temperature, the intensity of emitted light → 0 as the wavelength → 0
It increases to some maximum intensity Imax at some wavelength
Black body radiation- Features1. Wien’s Displacement Law
maxT = 2.99 mm K (Constant)
max
T
T
Common observation with heated bodies; Red blue
Shorter wavelengths contribute more to the energy density as temperature is raised and
the color shifts t
(T λmax = 2.9 mm K)Estimation of the Temperatures of Stars
Maximum Emission of the Sun occurs at λmax = 490 nm. What is the surface temperature?
The Surface Temperature of Sun T = 2.9mmK/ λmax
= (2.9 x 10-3 m K) / (490 x 10-9 m) = 5918 K
Application of Wien’s Displacement Law
Black body radiation : features
2. Stefan-Boltzmann Law:
Emittance M = aT4
(Power emitted per unit Surface Area)
‘a’ =5.67 x 10-8 Wm-2K-4 Rapid increase with increasing temperature
Stephan-Boltzman Law ; Emittance
T =1000K, Emittance, M= 5.7Wm-2
What is the emittance at 3000K ?T=3000K, M= 34 x 5.7Wm-2
Emittance : Area under the curve
Rapid increase with increasing temperature
M3000K = 81 x M1000K
Attempted explanation of black body radiation with classical mechanics
Rayleigh-Jeans law
Main assumptions
Electromagentic radiation was regarded as waves in jelly like ‘ether’
Ether could oscillate at any frequency so waves could exist in it of any wavelength
Rayleigh-Jeans Theory
Expt
Black body radiation : Rayleigh-Jeans formula
Energy density d is the energy per unit volume associated with radiation of wavelength from to +d, and is proportional to the
emittance :
Rayleigh-Jeans formula : d =k
d
Consequences
Works at long wavelengths (low frequencies) but fails badly at short wavelengths( high frequencies) As λ decreases, ρ increases without going through maximum
Oscillations of short wavelength areOscillations of short wavelength arestrongly excited at room temperaturestrongly excited at room temperature
k
dd =
Rayleigh-Jeans Formula:
d =
The function rises without bound as decreases
•Even cold objects would emit UV and visible!
Black body radiation : UV Catastrophe
k
d