1. Electron Configuration
Unit 4 - Electrons in Atoms
Electron Configuration

2. Atomic Model Review
Bohr – Electrons are found in orbitals around the nucleus
De Broglie – Electrons behave like waves
Consensus – Electrons are found in clouds around the nucleus

3. Quantum Mechanical Model
There are several energy levels occupied by electrons
Energy levels are represented by a positive number
As the distance from the nucleus increases, the number increases

4. Quantum Model
n=3
n=2
n=1
Nucleus

5. Quantum Model
There are several types of orbitals that can occur in an energy level
Orbitals have a specific shape and are represented by a lowercase letter

6. Quantum Model
s-orbital – SPHERICAL – 1 orbital

7. Quantum Model
p-orbital – BOWTIE – 3 orbitals

8. Quantum Model
d-orbital – CLOVERLEAF – 5 orbitals

9. Quantum Model
f-orbital – COMPLICATED!  – 7 orbitals

10. Quantum Model
Different energy levels have different types of orbitals.
1st energy level - s orbital
2nd energy level – s & p orbitals
3rd energy level – s, p, & d orbitals
4th energy level – s, p, d, & f orbitals

11. Quantum Model – Hog Hilton
3p ___ ___ ___ 3s ___ 2p ___ ___ ___ 2s ___ 1s ___

12. I KNOW HOW MANY Electrons an atom has… but how do the electrons FIT INTO THE ORBITALS??

13. General Rules
Pauli Exclusion Principle
Each orbital can hold TWO electrons with opposite spins.

14. General Rules
Aufbau Principle
Electrons fill the lowest energy orbitals first.
“Lazy Tenant Rule”

15. Aufbau Principle

16. General Rules
Hund’s Rule
Within a sublevel, place one e- per orbital before pairing them.
“Empty Bus Seat Rule”
WRONG
RIGHT

17. 1s2 2s2 2p4 O Notation 1s 2s 2p 8e- Orbital Diagram
Electron Configuration
1s2 2s2 2p4

18. Practice… Helium (He) Carbon (C) Sodium (Na) Phosphorus (P)
Nitrogen (N)
Aluminum (Al)
Calcium (Ca)
Argon (Ar) 18

19. Notation
There’s an easier way to figure out electron configurations
We can use our handy-dandy, trusty periodic table

20. Periodic Patterns s p d f 1 2 3 4 5 6 7 6 7
© 1998 by Harcourt Brace & Company

21. 1s1 C. Periodic Patterns 1st column of s-block 1st Period s-block
Example - Hydrogen
1s1
1st column of s-block
1st Period
s-block

22. Periodic Table Patterns
Period # (Row #) = Energy Level
Subtract 1 for d
Subtract 2 for f

23. Use the periodic table…
Helium (He)
Carbon (C)
Sodium (Na)
Phosphorus (P)
Iron (Fe)
Zirconium (Zr)
Calcium (Ca)
Iodine (I)

24. Notation – A Shorter Way!
Noble gas – column on the far right of the periodic table
Last energy level is full of electrons
Like a full floor of the Hog Hilton
Examples
He – 1s2
Ar – 1s2 2s2 2p6 3s2 3p6

25. Notation
We can abbreviate the full energy levels by using noble gases
Example - Sulfur

26. S 16e- 1s2 2s2 2p6 3s2 3p4 S 16e- [Ne] 3s2 3p4 Notation
Longhand Configuration
S 16e-
1s2
2s2
2p6
3s2
3p4
Shorthand Configuration
S 16e- [Ne] 3s2 3p4

27. Shorthand Notation
Example - Germanium
[Ar]
4s2
3d10
4p2

28. Shorthand Notation
Sulfur (S)
Tin (Sn)
Barium (Ba)
Silver (Ag)

29. S 16e- 1s2 2s2 2p6 3s2 3p4 Valence Electrons
The electrons found in the outermost shell or level
S 16e-
1s2
2s2
2p6
3s2
3p4
Core Electrons
Valence Electrons

30. Periodic Table Patterns
Group # (Column #) = Total # of valence electrons
True for s & p block
d & f blocks are weird… 

31. Lewis Dot Diagrams
Represents the number and placement of valence electrons in an atom

32. Lewis Dot Diagrams
Remember your electron rules
Be single before you double!
Electrons want to be far apart!
Since we’re only looking at the s & p blocks, the total number will be 8 or less

33. Lewis Dot Diagrams
Example – OXYGEN
How many valence electrons?
Write the element symbol
Fill in the dots

34. Stability Full energy level Full orbital (s, d, f)
Half-full orbital (p, d, f)

35. Stability Electron Configuration Exceptions Copper
EXPECT: [Ar] 4s2 3d9
ACTUALLY: [Ar] 4s1 3d10
Copper gains stability with a full d-orbital.

36. Stability Electron Configuration Exceptions Chromium
EXPECT: [Ar] 4s2 3d4
ACTUALLY: [Ar] 4s1 3d5
Chromium gains stability with a half-full d-orbital.

37. Stability – Ion Formation
Ion = charged atom; not neutral
Atoms gain or lose electrons to become more stable
More stable = noble gas configuration

38. Ground State Energy level that an electron normally occupies
State of lowest energy for an electron
Hogs are lazy & don’t like to climb stairs

39. Ground State
When an electron temporarily occupies an energy level GREATER than its ground state, it is in an EXCITED state
Excitement occurs when an electron absorbs a PHOTON (light emitting particle)
So when an electron RETURNS to its ground state, it will emit a PHOTON

40. Ground State  Excited State

41. Excited State  Ground State

42. Here’s the cool part!
The color of the emitted light depends on the amount of energy in the photon which depends on the wavelength

43. Flame Test
Can be used to identify unknown metals

45. Fume Hood