1. Chemistry 103
Lecture 6

2. Outline I. Electronic Structure Classical vs. Quantum Mechanics
Orbitals/Quantum Numbers
Electron Configurations

3. Learning Check
1. Which of the following pairs are isotopes of the same
element?
2. In which of the following pairs do both atoms have
8 neutrons?
A. 15X 15X
B. 12X 14X
C. 15X 16X
7 8

4. Electronic Structure - Quantum Mechanics
Nature of Electrons in Atoms

5. Modern Periodic Table
Periodic Law of the Elements – when elements are arranged in a particular order (increasing atomic number), elements of similar properties occur at periodic intervals
The Theoretical basis for the periodic
law lies in electronic theory
(Nature of the electrons in an atom)

6. Classical Physics
In the late 1800’s, Classical (Newtonian) Physics worked so well for the macroscopic world, most academics thought we had discovered all there was to know about the subject

7. Classical Mechanics
There is no limit to the number of observables we can measure simultaneously
These observables are continuous

8. Quantum Mechanics
Unfortunately, extremely small particles (electrons) do not follow the laws of classical (Newtonian) physics. The new physics that mathematically treats small particles is called Quantum Mechanics.

9. Periodicity of Periodic Table
Objective: Placing Electrons about the Nucleus
of an Atom for a Particular Element.
MODEL DEVELOPED
(Quantum Numbers)
APPLICATION
(Electron Configurations)

10. Quantum Model
Attempts to explain certain properties of light’s interaction with matter. One early experimental observation that could not be explained classically:
Emission spectra of heated gases.

11. Light
To embark upon the topic of quantum mechanics, we need to understand the nature of light.

12. Electromagnetic Spectrum
The electromagnetic spectrum
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13. Light Is a Form of Energy
Light is a form of electromagnetic radiation
Light travels as waves
Light carries radiant energy through space

14. Properties of Waves All waves have:
Wavelength: (l) horizontal distance between two corresponding points on a wave (units are usually m)
Frequency: (n) the number of complete wavelengths that pass a stationary point in a second
(units are usually Hz, s-1)

15. Question!
Which wave has a higher frequency?

16. Light Energy and Photons
Light is a stream of small particles called photons that have
Energy related to their frequency. Using Plank’s constant (h)
High energy with a high frequency
Low energy with a low frequency
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17. Electromagnetic Spectrum
The electromagnetic spectrum
Arranges forms of energy from lower to higher
Arranges energy from longer to shorter wavelengths
Shows visible light with wavelengths from nm
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18. Light Equations
All electromagnetic radiation moves through a vacuum at a specific speed.
c = 3.00 x 108 m/s
Wave Equations for light: c = ln
Energy Equation for light: E = hn
h = Planck’s constant
h = x J s

19. Light Equations Wave Equations for light: c = ln
Energy Equation for light: E = hn
Substituting frequency ( = c/)
E = hc


20. Light Calculations
What is the frequency of green light if it has a wavelength of 500. nm?

21. Light Calculations
A wavelength of 850. nm is used for fiber-optic transmission. What is the energy of this wavelength?

22. Spectrum White light that passes through a prism
Is separated into all colors called a continuous spectrum
Gives the colors of a rainbow
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23. Atomic Emission Spectrum
An atomic spectrum consists of lines
Of different colors formed when light from a heated element containing an element passes through a prism
spectrum
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24. Atomic Emission Spectra
When gases are heated, they give off light at certain frequencies.
In other words, atoms absorb or emit energy only at specific wavelengths (specific energies)
(Bodner and Pardue, 1995)

25. Quantum Mechanics Discrete values for observables - quantized values.
Probability - does not tell us where an electron is exactly, tells us the probability of an electron being at some point in space

26. Quantum Mechanics Summarized
A Mathematical Model that described what was being observed experimentally.
The Math defined the Theory.
The creators of Quantum Mechanics had difficulties when it came to interpretations made in a classical world.

27. In reference to “Quantum Mechanics”
Schrodinger ( )
“I don’t like it, and I’m sorry I ever had anything to do with it.”
Bohr ( )
“Anyone who is not shocked by Quantum Theory has not understood it.
Levine
“We cannot hope to obtain a proper understanding
of microscopic particles based on models
taken from our experiences in the macroscopic
world.”

28. Development of Theory - early steps

29. Bohr’s Model of the Atom
His Goal was to create a model that would explain the atomic spectrum of Hydrogen
Electrostatic Quandary
Postulates that there are only certain positions about the nucleus an electron can reside - STATIONARY STATES OF MOTION

30. Bohr’s Model of the Atom
When electrons absorb energy (in the form of light), they move from a lower energy level to a higher one.
When electrons move from a higher energy level to a lower energy level, they give off energy in the form of light (“emission”)

31. Electron Energy Levels
Electrons are arranged in
specific energy levels that
Are labeled n = 1, n = 2, n = 3, and so on
Increase in energy as n increases
Have the electrons with the lowest energy in the first energy level (n=1)closest to the nucleus
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32. Energy Level Changes
An electron absorbs energy to “jump” to a higher energy level.
When an electron falls to a lower energy level, energy is emitted.
In the visible range, the emitted energy appears as a color.
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33. Adding Probability
The very nature of locating an electron’s position causes uncertainty it another property (kinetic energy).
Can’t know both simultaneously - UNCERTAINTY

34. Quantum Numbers
An introduction into the math behind the theory.

35. Quantum Numbers - The Model
Shell (n)

36. QUANTUM NUMBERS Primary or Shell Quantum number (n = 1, 2, 3…)
(Bohr’s Model interpretation & notation)
Electron Shell
A region of space about a nucleus that contains electrons that have approximately the same energy and that spend most of their time approximately the same distance from the nucleus

37. Quantum Numbers - The Model
Shell (n)
Subshell (l)
l= l= l= l=3

38. Electron Subshells/Sublevels
Every shell (n) has subshell(s) (l)
l = 0, 1, … n - 1
Discribes the spatial distribution for an electron (PROBABILITY)
l = 0 (s), l = 1(p), l = 2, (d), l = 3 (f), …

39. Electron Orbitals (n & l )
Region of space where two electrons are likely to be found (90% probability)
Have different shapes depending on which subshell (l quantum number) they are in

40. Quantum Numbers & Orbitals
n = 1 , l = 0
First shell or energy level, you have one orbital: 1s
An “s” orbital as a spherical shape around
the nucleus

41. Quantum Numbers and Orbitals
l = Orbital Name 2s
l = 1 Orbital Name 2p

42. s Orbitals An s orbital Has a spherical shape around the nucleus
Increases in size around the nucleus as the energy level n value increases
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43. Quantum Numbers & Orbitals
n = 3 l = 0(s), l = 1(p), l = 2 (d)
n = l = 0(s), l=1(p), l=2(d), l=3(f)