1. Chapter 5
Electrons in Atoms

2. Bohr’s Model

3. Bohr’s Model
Electrons are found with fixed amounts of energy, like rungs of an uneven ladder
There is no “in between” energy
Energy Levels
Further away from the nucleus means more energy.
Fifth
Fourth
Third
Increasing energy
Second
First
Nucleus

4. Drawing Bohr Diagrams Find out which period (row) your element is in.
Elements in the 1st period have one energy level.
Elements in the 2nd period have two energy levels, and so on.
The first energy level can hold two electrons
All other energy levels hold eight electrons

5. C Bohr Diagrams Draw a nucleus.
Carbon is in the 2nd period, so it has two energy levels, or shells.
Draw the shells around the nucleus.
Add the electrons
Carbon has 6 electrons C

6. C Bohr Diagrams Draw the first two in energy level one
Go to the next energy level, add one at a time -starting on the right side and going counter clock-wise. C

7. Bohr Diagrams
Try the following elements on your own: H O Al C

8. H Bohr Diagrams Try the following elements on your own: H – 1 electronAl H

9. Bohr Diagrams O Try the following elements on your own: H
O - 8 electrons Al O

10. Bohr Diagrams Al Try the following elements on your own: H O
Al - 13 electrons Al

11. The Quantum Mechanical Model
Energy is quantized. That means it comes in chunks.
Quanta - the amount of energy needed to move from one energy level to another.
Quantum leap in energy.
Schrödinger derived an equation that described the energy and position of the electrons in an atom
Treated electrons as waves

12. The Quantum Mechanical Model
The electron is found inside a blurry “electron cloud”
An area where there is a chance of finding an electron.
Draw a line at 90 %

13. The Quantum Mechanical Model
Herriman High Chemistry
The Quantum Mechanical Model
The propeller blade has the same probability of being anywhere in the blurry region, but you cannot tell its location at any instant. The electron cloud of an atom can be compared to a spinning airplane propeller.
The electron cloud of an atom is compared here to photographs of a spinning airplane propeller. a) The airplane propeller is somewhere in the blurry region it produces in this picture, but the picture does not tell you its exact position at any instant. b) Similarly, the electron cloud of an atom represents the locations where an electron is likely to be found.

14. Atomic Orbitals
Principal Quantum Number (n) = the energy level of the electron.
Within each energy level the complex math of Schrödinger's equation describes several shapes.
These are called atomic orbitals
Regions where there is a high probability of finding an electron.

15. S orbitals 1 s orbital for every energy level Spherical shaped
Each s orbital can hold 2 electrons
Called the 1s, 2s, 3s, etc.. orbitals.

16. P orbitals Start at the second energy level 3 different directions
3 different shapes (dumbell)
Each can hold 2 electrons

17. P Orbitals

18. D orbitals Start at the third energy level 5 different shapes
Each shape can hold 2 electrons

19. F orbitals Start at the fourth energy level
Have seven different shapes
2 electrons per shape

20. F orbitals
Images
J mol

21. Max/Total Electrons S 2 electrons P 6 electrons D 10 electrons
F electrons
1 shape
3 shapes
5 shapes
7 shapes

23. Filling order Lowest energy fill first. The energy levels overlap
The orbitals do not fill up exactly in order of energy level.
Counting system
Each box is an orbital shape
Room for two electrons

24. Increasing energy 7s 2p 3p 4p 5p 6p 7p 3d 4d 5d 6d 6s 5s 4f 5f 4s 3s

25. Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p

26. Electron Configuration
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Electron Configuration
Electron configuration is the arrangement of electrons in an atom
Electrons are assigned quantum numbers that work like an address of an electron
Quantum numbers specify the properties of atomic orbitals and the properties of electrons in orbitals.

27. Rule #1(Aufbau principle)
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Rule #1(Aufbau principle)
Electrons enter the lowest available energy orbital first

29. Rule # 2 (Pauli exclusion principle)
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Rule # 2 (Pauli exclusion principle)
There are a maximum of 2 electrons per orbital which means if there are two electrons in the same orbitals they must have opposite spins
One spins clockwise, the other counter clockwise

30. Herriman High Chemistry
Rule #3 (Hund’s Rule)
For p, d, f orbitals  1 e- enters each orbital until all contain 1 e-
Then a 2nd e- added 1 at a time

31. Example: Nitrogen atomic # 7
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Example: Nitrogen atomic # 7 1s 2s 2p
Or Shorthand:
1s2 2s2 2p3

32. The easy way to remember
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2
2 electrons

33. Fill from the bottom up following the arrows
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2 2s2
4 electrons

34. Fill from the bottom up following the arrows
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2 2s2 2p6 3s2
12 electrons

35. Fill from the bottom up following the arrows
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2 2s2 2p6 3s2 3p6 4s2
20 electrons

36. Light
The study of light led to the development of the quantum mechanical model.
Light is a kind of electromagnetic radiation.
Electromagnetic radiation includes many kinds of waves
All move at 3.00 x 108 m/s ( c)

37. Parts of a wave
Crest
Wavelength
Amplitude
Origin
Trough

38. Parts of Wave Origin - the base line Crest - high point
Trough - Low point
Amplitude - distance from origin to crest
Wavelength - distance from crest to crest
Wavelength - is abbreviated l -Greek letter lambda.

39. Frequency
The number of waves that pass a given point per second.
Units are cycles/sec or hertz (Hz)
Abbreviated n - the Greek letter nu
c = ln

40. Frequency and wavelength
Are inversely related
As one goes up the other goes down.
Different frequencies of light is different colors of light.
There is a wide variety of frequencies
The whole range is called a spectrum

41. Spectrum Low energy High energy Radiowaves Microwaves Infrared .
Ultra-violet
X-Rays
GammaRays
Low Frequency
High Frequency
Long Wavelength
Short Wavelength
Visible Light

42. Light is a Particle Energy is quantized. Light is energy
Light must be quantized
These smallest pieces of light are called photons.
Energy and frequency are directly related.

43. Energy and frequency E = h x n E is the energy of the photon
n is the frequency
h is Planck’s constant
h = x Joules sec.

44. The Math in Chapter 5 Only 2 equations c = ln E = hn
c is always x 108 m/s
h is always x J s

45. Examples
What is the frequency of red light with a wavelength of 4.2 x 10-5 cm?
What is the wavelength of KFI, which broadcasts at with a frequency of 640 kHz?
What is the energy of a photon of each of the above?

46. How color tells us about atoms
Atomic Spectrum
How color tells us about atoms

47. Prism
White light is made up of all the colors of the visible spectrum.
Passing it through a prism separates it.

48. If the light is not white we get bands of color
These are called line spectra
They are unique to each element.
These are emission spectra

49. An explanation of Atomic Spectra

50. Where the electron starts
When we write electron configurations we are writing the lowest energy.
The energy level an electron starts from is called its ground state.

51. Changing the energy
Let’s look at a hydrogen atom

52. Changing the energy
Heat or electricity or light can move the electron up energy levels

53. Changing the energy
As the electron falls back to ground state it gives the energy back as light

54. Changing the energy May fall down in steps
Each with a different energy

55. The Bohr Ring Atom
n = 4
n = 3
n = 2
n = 1

56. { { {

57. Ultraviolet
Visible
Infrared
Further they fall, more energy, higher frequency.
This is simplified
the orbitals also have different energies inside energy levels
All the electrons can move around.

58. Quantum mechanics
Quantum mechanics explains how the very small behaves.
Quantum mechanics is based on probability because it is impossible to know exactly the speed and position of a particle.
The better we know one, the less we know the other.
The act of measuring changes the properties.
This is called the Heisenberg Uncertainty Principle

59. More obvious with the very small
To measure where a electron is, we use light.
But the light moves the electron
And hitting the electron changes the frequency of the light.

60. After Before Photon changes wavelength Photon
Electron changes velocity
Moving Electron