1. Unanswered Questions
Rutherford’s model did not address the following questions:
What is the arrangement of electrons in the atom?
What keeps the electrons from converging on the nucleus?
What accounts for the differences in chemical behavior among elements?

2. Bohr Model of the Atom
Electrons movement around the nucleus is restricted to a particular circular orbit. The “Planetary” model.
Each orbit is associated with a certain amount of energy
The larger the orbit (farther away from the nucleus) the greater the energy
In order to move from one orbit to the next, an electron has to absorb a quantum of energy
Bohrs model was limited to explaining the behavior of hydrogen
The minimum amount of energy required to move an electron from one level to another

3. Quantum Mechanical Model
Like Bohr, electrons energies are limited to a certain value
Unlike Bohr, electrons do not travel in prescribed paths.
Electrons travel within a particular volume of space surrounding the nucleus
The probability of finding an electron in a particular region of space is represented as a cloud of electrons.

4. Organization of Electrons in an Atom
Energy Levels (aka principal quantum numbers) n=1,2,3,4,5,6,7
Energy levels increase as distance from the nucleus increases
Sublevels (s,p,d,f)
Volume of space defined by a collection of orbitals
Orbitals
Shapes
Sharp, principal, diffuse, and fundamental

5. Ground-State Electron Configuration
Arrangement of electron in an atom at rest
The lowest energy arrangement is the most stable
Three Rules that govern how electrons can be arranged in an atom:
Aufbau Principle
Each electron occupies the lowest energy orbital available
Pauli Exclusion Principle
A maximum of two electrons can occupy a single orbital
Hund’s Rule
Electrons with the same spin must occupy each orbital before electrons with opposite spins can occupy each orbital

6. Orbital Filling Sequence
(subshell)
(Energy Level)

7. Benchmark
If you haven’t done so already, you should read pages in your textbook. In addition to the material we have covered in class this information should enable you to do the following:
Written work questions on p
# 24, 28, 35, 36, 38, 39a, 50 p. 153 #2

8. Orbital Filling Diagram
Fluorine (atomic #9)
Orbital Diagram 2 2 5
Electron Configuration

10. Nobel Gas Configuration
To shorten the amount of writing required to represent the configuration of elements with large numbers of electrons, the symbol for the noble gas that directly precedes an element can represent all of the electrons up to that point.
Long Hand Short Hand
1s2 2s2 2p6 3s2 3p6 4s2
[Ar] 4s2

11. Exceptional Electron Configurations
Not all electron configurations abide by Aufbau’s principle. Half-filled sub-levels are not as stable as filled sublevels, but they are more stable than other configurations.
Ex. Chromium
According to Aufbau
More stable configuration
1s2 2s2 2p6 3s2 3p6 4s23d4

12. Ground State and Excited State Electron Configurations
The ground state electron configurations represents electrons in their lowest energy states, following Aufbau’s Principal
Kground: 1s2 2s2 2p6 3s2 3p6 4s1
In the excited state electrons change position in the atom as they absorb energy, moving to higher energy sublevels or skipping energy levels all together.
Kexcited: 1s2 2s2 2p6 3s2 3p5 4s2 or
Kexcited: 1s2 2s2 2p6 3s2 3p6 4p1

13. Benchmark
If you haven’t done so already, you should read pages in your textbook. In addition to the material we have covered in class this information should enable you to do the following:
Written work questions on p # 64, 68, 71
p. 153 # 6,8,10

14. Chemical Behavior Related to the Arrangement of Electrons
In the early 1900’s scientist observed that when they heated elements in a flame, the elements emitted colored light. Analysis of the light led scientist to determine that the arrangement of electrons in an atom is related to the elements chemical behavior.

15. Understanding Light – Characteristics of Waves
Using the word bank below, match the words to the lettered parts of the diagram A D C
B = 3/s
1 sec E
Frequency Amplitude Peak Trough Wavelength

16. Waves Characteristics
Wavelength (l) the shortest distance between two equivalent points on a wave.
(unit of measure: meters, centimeters, or nanometers)
Frequency (v) the number of waves that pass a given point per second.
(unit of measure: Hz, waves/second, /s, s-1) c l v
Waves
c=lv
Speed of Light (c) = 3.0 x 108m/s

17. Relationship Between Wavelength and Frequency
c=lv
Frequency
Wavelength

18. Electromagnetic Spectrum
Electromagnetic radiation – Form of energy that exhibits wave-like behavior.
Electromagnetic spectrum – encompasses all forms of electromagnetic radiation. The only differences between each form is their characteristic wavelengths and frequencies.
White Light – a continuous spectrum of colors, each with a unique wavelength and frequency.

19. The Electromagnetic Spectrum
Which of the following waves has the longest wavelength? Which has the greatest frequency?

20. Line Spectra

21. Einstein’s Contribution
Explained that electromagnetic radiation behaves both like waves and particles.
Ephoton=hv
Photon – a particle of electromagnetic radiation with no mass that carries a quantum of energy.

22. Equantum=hv Relationships between wavelength, frequency and Energy
E = energy
h = Planck’s constant=6.626 x 10-34J
V = frequency
Relationships between wavelength, frequency and Energy
Energy
Energy
Frequency
Wavelength
Wavelength
Frequency

23. Electrons as Waves (Louis de Broglie)
de Broglie proposed the idea that all particles have wavelengths
Wavelengths of large bodies are too small to observe and therefore principals of classical physics best describes their movement
Quantum mechanics provides a more suitable explanation of the movement of subatomic particles

24. Photoelectric Effect
Electrons are emitted from a metal’s surface when light of a certain minimum frequency of 1.14 x 1015 Hz shines on the surface.
(Conversion of light energy to electrical energy)

25. Heisenberg Uncertainty Principle
Premise: It is impossible to make any measurement on an object without disturbing the object.
The position of electron can be determined by shooting photons at electrons in an atom
It is impossible to know precisely both the velocity and position of a particle at the same time

26. Benchmark
If you haven’t done so already, you should read pages in your textbook. In addition to the material we have covered in class this information should enable you to do the following:
Written work questions on p # 45, 55, 61, 63, 75, 83, 92, 94
p. 153 # 4, 12