1. Chapter 8: Electrons in Atoms
Chemistry 140 Fall 2002
CHEMISTRY
Ninth
Edition
GENERAL
Principles and Modern Applications
Petrucci • Harwood • Herring • Madura
Chapter 8: Electrons in Atoms
Iron rusts
Natural gas burns
Represent chemical reactions by chemical equations.
Relationship between reactants and products is STOICHIOMETRY
Many reactions occur in solution-concentration uses the mole concept to describe solutions
Philip Dutton
University of Windsor, Canada
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General Chemistry: Chapter 8
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2. General Chemistry: Chapter 8
Contents
8-1 Electromagnetic Radiation
8-2 Atomic Spectra
8-3 Quantum Theory
8-4 The Bohr Atom
8-5 Two Ideas Leading to a New Quantum Mechanics
8-6 Wave Mechanics
8-7 Quantum Numbers and Electron Orbitals
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3. Contents 8-8 Quantum Numbers
8-9 Interpreting and Representing Orbitals of the Hydrogen Atom
8-9 Electron Spin
8-10 Multi-electron Atoms
8-11 Electron Configurations
8-12 Electron Configurations and the Periodic Table
Focus On Helium-Neon Lasers
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4. 8-1 Electromagnetic Radiation
Electric and magnetic fields propagate as waves through empty space or through a medium.
A wave transmits energy.
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5. General Chemistry: Chapter 8
EM Radiation
Low 
High 
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6. Frequency, Wavelength and Velocity
Frequency () in Hertz—Hz or s-1.
Wavelength (λ) in meters—m.
cm m nm  pm
(10-2 m) (10-6 m) (10-9 m) (10-10 m) (10-12 m)
Velocity (c)—  108 m s-1.
c = λ λ = c/ = c/λ
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7. Electromagnetic Spectrum
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8. Constructive and Destructive Interference
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9. Examples of Interference
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10. General Chemistry: Chapter 8
Refraction of Light
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11. General Chemistry: Chapter 8
Chemistry 140 Fall 2002
9-2 Atomic Spectra
(a) (b) (c) (d) (e)
Hydrogen
Helium
Lithium
Sodium
Potassium
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12. General Chemistry: Chapter 8
Atomic Spectra
Helium
Hydrogen
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13. General Chemistry: Chapter 8
Chemistry 140 Fall 2002
8-3 Quantum Theory
Blackbody Radiation:
Heated bodies emit light
Blackbody Radiation
I  λ
Classical theory predicts continuous increase of intensity with wavelength.
1900, Max Planck made the revolutionary proposal that ENERGY, LIKE MATTER, IS DISCONTINUOUS.
Introduces the concept of QUANTA of energy.
h = x J s.
Max Planck, 1900
є = h
Energy, like matter, is discontinuous.
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14. General Chemistry: Chapter 8
Black Body Radiation
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15. The Photoelectric Effect
Heinrich Hertz, 1888
Light striking the surface of certain metals causes ejection of electrons.
 > o
threshold frequency
#e-  I
ek  
Albert Einstein 1905
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16. The Photoelectric Effect
Chemistry 140 Fall 2002
The Photoelectric Effect
Phonton strikes a bound eletron which absorbges the energy, if binding energy (known as the work function) is less than photon energy, the e- is ejected.
Stopping voltage of photoelectrons as a function of frequency of incident radiation.
Threshold frequency found by extrapolation.
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17. The Photoelectric Effect
At the stopping voltage the kinetic energy of the ejected electron has been converted to potential. 1
mu2 = eVs 2
At frequencies greater than o:
Vs = k ( - o)
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18. The Photoelectric Effect
eVo
Ek = eVs
Eo = ho
o = h
eVo, and therefore o, are characteristic of the metal.
Conservation of energy requires that: 1
Ephoton = Ek + Ebinding
h =
mu2 + eVo 2 1
Ek = Ephoton - Ebinding
eVs =
mu2 = h - eVo 2
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19. General Chemistry: Chapter 8
Chemistry 140 Fall 2002
8-4 The Bohr Atom
E =
-RH n2
Electrons move in circular orbits about the nucleus.
Motion described by classical physics.
Fixed set of stationary states (allowed orbits).
Governed by angular momentum: nh/2π, n=1, 2, 3….
Energy packets (quanta) are absorbed or emitted when electrons change stationary states.
The integral values are allowed are called quantum numbers.
RH =  J
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20. General Chemistry: Chapter 8
Energy-Level Diagram
ΔE = Ef – Ei =
-RH
nf2
ni2 –
= RH (
ni2 1
nf2 –
) = h = hc/λ
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21. Ionization Energy of Hydrogen1 1
ΔE = RH ( –
) = h
ni2
nf2
As nf goes to infinity for hydrogen starting in the ground state:
h = RH (
ni2 1
) = RH
This also works for hydrogen-like species such as He+ and Li2+.
h = -Z2 RH
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22. Emission and Absorption Spectroscopy
Chemistry 140 Fall 2002
Emission and Absorption Spectroscopy
In spite of its accomplishments, there are weaknesses in Bohr theory.
Can’t explain
spectra of species with more than one electron,
effect of magnetic fields on emission spectra
It is an uneasy mixture of classical and non-classical physics.
Modern quantum theory replaced Bohr theory in 1926.
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23. 8-5 Two Ideas Leading to a New Quantum Mechanics
Wave-Particle Duality
Einstein suggested particle-like properties of light could explain the photoelectric effect.
Diffraction patterns suggest photons are wave-like.
deBroglie, 1924
Small particles of matter may at times display wavelike properties.
Louis de Broglie
Nobel Prize 1918
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24. de Broglie and Matter Waves
Chemistry 140 Fall 2002
de Broglie and Matter Waves
E = mc2
h = mc2
h/c = mc = p
p = h/λ
λ = h/p = h/mu
If matter waves exist for small particles, then beams of particles such as electrons should exhibit the characteristic properties of waves: diffraction.
General Chemistry: Chapter 8
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25. General Chemistry: Chapter 8
Chemistry 140 Fall 2002
X-Ray Diffraction
1927 Davisson aand Germer – Diffraction of slow electrons from a Ni crystal.
1927 Thomson- diffraction from thin metal foil
Nobel prize shared by Davisson and Thomson in 1937.
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26. The Uncertainty Principle
Werner Heisenberg
Δx Δp ≥ 4π
Heisenberg and Bohr
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27. General Chemistry: Chapter 8
8-6 Wave Mechanics
Standing waves.
Nodes do not undergo displacement.
λ = , n = 1, 2, 3… 2L n
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28. General Chemistry: Chapter 8
Wave Functions
ψ, psi, the wave function.
Should correspond to a standing wave within the boundary of the system being described.
Particle in a box.
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29. Probability of Finding an Electron
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30. Wave Functions for Hydrogen
Schrödinger, Eψ = H ψ
H (x,y,z) or H (r,θ,φ)
ψ(r,θ,φ) = R(r) Y(θ,φ)
R(r) is the radial wave function.
Y(θ,φ) is the angular wave function.
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31. Principle Shells and Subshells
Principle electronic shell, n = 1, 2, 3…
Angular momentum quantum number, l = 0, 1, 2…(n-1)
l = 0, s
l = 1, p
l = 2, d
l = 3, f
Magnetic quantum number, ml= - l …-2, -1, 0, 1, 2…+l
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32. General Chemistry: Chapter 8
Orbital Energies
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33. 9-8 Interpreting and Representing the Orbitals of the Hydrogen Atom.
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34. General Chemistry: Chapter 8
s orbitals
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35. General Chemistry: Chapter 8
p Orbitals
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36. General Chemistry: Chapter 8
p Orbitals
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37. General Chemistry: Chapter 8
d Orbitals
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38. 9-9 Electron Spin: A Fourth Quantum Number
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39. Stern-Gerlach Experiment
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40. 8-10 Multi-electron Atoms
Schrödinger equation was for only one e-.
Electron-electron repulsion in multi-electron atoms.
Hydrogen-like orbitals (by approximation).
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41. Penetration and Shielding
Zeff is the effective nuclear charge.
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42. 8-11 Electron Configurations
Aufbau process.
Build up and minimize energy.
Pauli exclusion principle.
No two electrons can have all four quantum numbers alike.
Hund’s rule.
Degenerate orbitals are occupied singly first.
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43. General Chemistry: Chapter 8
Orbital Energies
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44. General Chemistry: Chapter 8
Orbital Filling
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45. Aufbau Process and Hunds Rule
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46. General Chemistry: Chapter 8
Filling p Orbitals
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47. General Chemistry: Chapter 8
Filling the d Orbitals
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48. General Chemistry: Chapter 8
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49. 8-12 Electron Configurations and the Periodic Table
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50. End of Chapter Questions
Test your decisions that you make while solving a problem by continuing on the path and seeing if they turn out to be:
a) sensible and b) useful.
You must always validate your assumptions at some point in your solution.
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