1. Chapter 4-Arrangement of Electrons in Atoms
Carbon:1s22s22p2

2. Photoelectric Effect(Early 1900’s)
Photoelectric effect-Heated metal absorbs energy and causes electrons to get excited.
Photon of energy-Particle of light that is carrying enough energy to excite an electron
It takes a quantum of energy to excite an electron
Quantum: The amount of energy needed to move an electron from one energy level to the next. -
Woohoo!!
Photon
Quantum of energy

3. Relationship between an Atom and Energy
Ground State: The lowest energy state of an atom.
Absorb- When an atom receives energy then it Absorbs energy.
Excited State: The state in which an atom has absorbed energy. The electrons are further away from the nucleus.
Emit- When an atom gives off energy then it is emitting energy.

4. How did Bohr use the photoelectric effect to come up with fixed energy levels?
With Rutherford’s model, all amounts of energy should have caused the photoelectric effect to happen but only certain amounts of energy actually do, therefore, there must be levels for the electrons to try and reach. Also, You get distinct color bands which suggests that electrons are jumping to and from specific places (and releasing specific amounts of energy) and not just randomly buzzing around the nucleus.

5. Bohr Model
Niels Bohr -developed a model of a hydrogen atom that showed the electron circling the nucleus in a fixed path.
He determined that each energy level had a particular amount of electrons that could occupy each level.
2 things wrong with Bohrs Model:
It only worked for Hydrogen
why?
It didn’t explain the atoms bonding ability or chemical behavior

6. Bohr vs Quantum Models + 3rd Energy Level 2nd Energy Level
1st energy level

7. The Quantum Model
Heisenberg Uncertainty Principle-It is impossible to know both the position and velocity of an electron at the same time.
Mice and Cockroaches!!
Quantum Model-Model that shows the possible or probable location of all electrons in an atom
Orbitals- three dimensional region around the nucleus that indicates the probable location of an electron.
90% of the time

8. Quantum Numbers
Quantum Numbers- 4 numbers used to tell us where an electron is located in an atom
1. Principal Quantum Number (n)
2. Angular Momentum Quantum Number ( l )
3. Magnetic Quantum Number
4. Spin Quantum Number

9. Our Goal: Electron Configurations
Noble Gas Configuration
H 1s1
He 1s2
Li 1s22s1
Be 1s22s2
B 1s22s22p1
C 1s22s22p2
N 1s22s22p3
O 1s22s22p4
F 1s22s22p5
Ne 1s22s22p6
H 1s1
He 1s2
Li [He]2s1
Be [He]2s2
B [He]2s22p1
C [He]2s22p2
N [He]2s22p3
O [He]2s22p4
F [He]2s22p5
Ne [He]2s22p6

10. 1-Principal Quantum # Tells us which energy level an electron is in
Symbolized by n
Can have a value of 1,2,3,4,5,6,or 7
Example n=3 means the electron is in the 3rd energy level.

11. 2-Angular Momentum Quantum #
Gives the shape of the orbital the electrons are making
s, p, d, or f

12. #2-Angular Momentum s Orbital
spherical or round shape (like a ball)
Can hold 2 electrons total
Lowest in energy
Periodic table Groups 1-2

13. #2-Angular Momentum p Orbital
p orbital can have THREE orientations(parts)
-orientated on the x axis
-orientated on the y axis
-orientated on the z axis
dumbbell shaped
Each dumbell can hold 2 e-
How many total electrons will be in a p orbital?
Periodic table Groups 13-18
Second lowest in energy

14. #2-Angular Momentum d Orbital
5 different orientations (parts)
Each part can hold 2 e-
How many total electrons can a d orbital hold?
Periodic table groups 3-12
Third in energy

15. #2-Angular Momentum f Orbital
f Orbital can have 7 orientations
Each shape can hold 2 e-
How many total electrons can an f orbital hold?
14 total e-
Shape not important
Periodic table groups: Lanthanides and Actinides (the two rows at the bottom)
Highest in energy

16. #2-Angular Momentum s Orbital
s sublevel can have only ONE orientation or part
spherical or round shape (like a ball)
Can hold 2 electrons total
Periodic table Groups 1-2
Lowest in energy

17. 3-Magnetic Quantum #
Tells us which plane, orientation, or axis the orbital is in

18. 4-Spin Quantum #
Tells us if the electron is spinning clockwise or counter-clockwise
:We will use these with Orbital Notation
Clockwise
Counter Clockwise

19. Aufbau principle
States that an electron occupies the lowest-energy Orbital that can receive it.
Electrons take the path of least resistance..Lazy Electrons -

20. Hund’s Rule
States that each part of an orbital should get 1 electron before any of the parts can have 2.
Don’t be stingy you have to share!!!
Each part of p,d, and f needs 1 electrons before any part can have 2.

21. Quantum Numbers
Pauli Exclusion Principle: no two electrons in the same atom can have the same set of quantum #s.
Ne 1s22s22p6

22. How to know where electrons fill?
Electrons always fill lowest energy level first (1,2,3,4,5,6,7)
Electrons fill lowest orbital in each energy level first (s,p,d,f)
Question you need to answer in your notes:
Why do electrons go back down to the 3rd energy level and fill the d orbital?

23. Electron Configuration Chart

24. Representing Electron Configurations
Four ways to show arrangement of electrons
1. Electron Configuration Notation(long)
2. Noble Gas Configuration(short cut)
3. Orbital Notation(arrows)
4. Electron Dot Notation(dots)

25. 1-Electron Configuration(long way)
Shows all electrons in atom
Gives
Energy Level
Shape of Orbital
Number of electrons in each orbital
Example: Hydrogen 1S1
# of electrons
Orbital Type
Main Energy Level

26. How to write electron configurations
Always start with 1s
“Read” the periodic table like a book.
Follow all the rules
When you have to jump to the next energy level, ALWAYS start back filling in the s orbital.
Remember that all energy levels have an s orbital.

27. Electron Configurations-period three elements
Na 1s22s22p63s1
Mg 1s22s22p63s2
Al 1s22s22p63s23p1
Si 1s22s22p63s23p2
P 1s22s22p63s23p3
S 1s22s22p63s23p4
Cl 1s22s22p63s23p5
Ar 1s22s22p63s23p6

29. Fourth period elements
K 1s22s22p63s23p64s1
Ca 1s22s22p63s23p64s2
Sc 1s22s22p63s23p64s23d1 Ti Zn
Ga 1s22s22p63s23p64s23d104p1 Ge As Se Br Kr

30. Exception to every rule
There are some exceptions to the Aufbau principal for elements 24 and 29
Cr: 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Cu: 1s2 2s2 2p6 3s2 3p6 4s1 3d10

31. Elements of the fifth period
Rb 1s22s22p63s23p64s23d104p65s1
Sr 1s22s22p63s23p64s23d104p65s2

32. Write the electron configuration notation for the following:
1. Boron (B)
2. Magnesium (Mg)
3. Argon (Ar)
4. Calcium (Ca)
5. Bromine (Br)

33. Noble gas configurations
-A short hand way of writing an electron configuration using noble gases.
-First, determine what period the element is in.
-Second, put the noble gas in the previous period in [ ]. The noble gas in [ ]accounts for its atomic # of electrons.

34. Noble gas configurations
Third-start filling with the energy level that equals the period #.
Ex: write the noble gas configuration for sodium, Na
Na is in the 3rd period, so use the noble gas in the 2nd period, which is Ne
[Ne]3s1

35. Noble gas configurations
Compare the configuration of the noble gas Ne to all of the period 3 elements. All period 3 elements start off with Neon’s configuration
Ne 1s22s22p6
Na 1s22s22p63s1
Mg 1s22s22p63s2
Al 1s22s22p63s23p1
Si 1s22s22p63s23p2
P 1s22s22p63s23p3
S 1s22s22p63s23p4
Cl 1s22s22p63s23p5
Ar 1s22s22p63s23p6

36. Orbital Notation Coincides with electron configuration notation.
Orbital notation is a diagram that shows Hund’s rule.

37. Preparing for the Test
Go online to the Text Book
Work the following problems to prepare:
Page-124 (15-19)
Page-125 (20-37)
Page- 126 (38-41)

38. Dot notation Shows only valence shell (outer) electrons
Group 1 has 1 valence electron
Group 2 has 2 valence electrons
Group 13 has 3 valence electrons
Group 14 has 4 valence electrons
Group 15 has 5 valence electrons
Group 16 has 6 valence electrons
Group 17 has 7 valence electrons
Group 18 has 8 valence electrons - - - - -

39. Dot notation continued
First-write the symbol of the element
Second-determine the group of the element and decide # of outer electrons
Third- Place dots around the symbol to represent electrons in the outer shell