Chemistry 101 : Chap. 6 Electronic Structure of Atoms (1) The Wave Nature of Light (2) Quantized Energy and Photon (3) Line Spectra and Bohr Models (4) The Wave Behavior of Matter (5) Quantum Mechanics and Atomic Orbitals (6) Representations of Orbitals (7) Many Electron Atoms (8) Electron Configurations (9) Electron Configurations and Periodic Table
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Chemistry 101 : Chap. 6 Electronic Structure of Atoms (1) The Wave Nature of Light (2) Quantized Energy and Photon (3) Line Spectra and Bohr Models (4)
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Chemistry 101 : Chap. 6Chemistry 101 : Chap. 6
Electronic Structure of Atoms
(1) The Wave Nature of Light
(2) Quantized Energy and Photon
(3) Line Spectra and Bohr Models
(4) The Wave Behavior of Matter
(5) Quantum Mechanics and Atomic Orbitals
(6) Representations of Orbitals
(7) Many Electron Atoms
(8) Electron Configurations
(9) Electron Configurations and Periodic Table
Electronic StructureElectronic Structure
What is the electronic structure?
The way electrons are arranged in an atom
How can we find out the electronic structure experimentally ?
Analyze the light absorbed and emitted by substances
Is there a theory that explains the electronic structure of atoms?
Yes. We need “quantum mechanics” to explain the results from experiments
Wave Nature of LightWave Nature of Light
Electromagnetic Radiation :
Visible light is an example of electromagnetic radiation (EMR)
Electric Field
Magnetic Field
Wave Nature of LightWave Nature of Light
Properties of EMR
All EMR have wavelike characteristics
Wave is characterized by its wavelength, amplitude and
frequency
EMR propagates through vacuum at a speed of 3.00 108 m/s
(= speed of light = c)
Wave Nature of LightWave Nature of Light
Frequency () and wavelength ()
Frequency measures how many wavelengths pass through a point per second:
1 s
4 complete cycles pass
through the origin
= 4 s-1 = 4 Hz
Note that the unit of is m
= c
Wave Nature of LightWave Nature of Light
Higher frequencyLonger wavelength
Wave Nature of LightWave Nature of Light
Example : What is the wavelength, in m, of radio wave transmitted
by the local radio station WHQR 91.3 MHz?
Wave Nature of LightWave Nature of Light
Example : Calculate the frequency of radio wave emitted by a
cordless phone if the wavelength of EMR is 0.33m.
Physics in the late 1800’sPhysics in the late 1800’s
Universe
Matter (particles) Wave (radiation)
F = ma
Newton’s equation
Isaac Newton (1643-1727)
0
BJt
EB
Et
BE
Maxwell’s equation
James C. Maxwell (1831-1879)
The Failure of Classical TheoriesThe Failure of Classical Theories
In the late 1800, there were three important phenomena that
could not be explained by the classical theories
Black body radiation
Photoelectric effect
Line Spectra of atoms
Black Body RadiationBlack Body Radiation
Black body :
An object that absorbs all electromagnetic radiations that falls
onto it. No radiation passes through it and none is reflected.
The amount and wavelength of electromagnetic radiation
a black body emits is directly related to their temperature.
Hot objects emit light.
The higher the temperature, the higher the emitted frequency
Black Body RadiationBlack Body Radiation
wavelength (nm)
inte
nsity
visible region
“Ultraviolet catastrophe” classical theory predictssignificantly higher intensityat shorter wavelengths thanwhat is observed.
Black Body RadiationBlack Body Radiation
Classical Theory :
Electromagnetic radiation has only wavelike characters.
Energy (or EMR) can be absorbed and emitted in any amount.
Planck’s Solution :
Max Planck (1858 - 1947)
He found that if he assumed that energy
could only be absorbed and emitted in
discrete amounts then the theoretical and
experimental results agree.
1exp
8)(
5
kThc
hcI
Quantization of EnergyQuantization of Energy
Energy Quanta : Planck gave the name ``quanta’’ to the smallest
quantity of energy that can be absorbed or emitted as EMR.
E = h
h = Planck Constant = 6.626 10-34 Js
Energy of a quantumof EMR with frequency
frequency of EMR
NOTE : Energy of EMR is related to frequency, not intensity
NOTE : When energy is absorbed or emitted as EMR with a frequency , the amount of energy should be a integer multiple of h
Quantization of EnergyQuantization of Energy
Example : Calculate the energy contained in a quantum of EMR
with a frequency of 95.1 MHz.
Photoelectric EffectPhotoelectric Effect
Photoelectric Effect : When light of certain frequency strikes a
metal surface electrons are ejected. The velocity of ejected
electrons depend on the frequency of light, not intensity.
e- e- e-
e-
K.E.of ejected electron =
Energy of EMR Energy needed to release an e-
Light of a certain minimum frequency
is required to dislodge electrons from
metals
Photoelectric EffectPhotoelectric Effect
Einstein’s Solution: In 1905, Einstein explained photoelectric
effect by assuming that EMR can behave as a stream of particles,
which he called photon. The energy of each photon is given by
Ephoton = h
e- e- e-
K.E.e = h
incident photon energy
binding energy Kinetic energyof ejected electrons
Einstein’s discovery confirmed Planck’snotion that energy is quantized.
Energy, Frequency and Wavelength
Energy, Frequency and Wavelength
Example : Calculate the energy of a photon of EMR with a
wavelength of 2.00 m.
EMR: Is it wave or particle?EMR: Is it wave or particle?
Einstein’s theory of light poses a dilemma:
Is light a wave or does it consist of particles?
When conducting experiments with EMR using wave measuring
equipment (like diffraction), EMR appear to be wave
When conducting experiments with EMR using particle techniques
(like photoelectric effect), EMR appear to be a stream of particles
EMR actually has both wavelike and particle-like characteristics.
It exhibits different properties depending on the methods used
to measure it.
Continuous SpectrumContinuous Spectrum
Many light sources, including light bulb, produce light containing many different wavelengths
continuous spectrum
Line SpectrumLine Spectrum
When gases are placed under low pressure and high voltage,
they produces light containing a few wavelengths.
Line SpectrumLine Spectrum
Rydberg equation: The positions of all line spectrum () can be