1. Electronic Configurations

2. Follow the subshells like a ‘book’ across the periodic table.
How to…
Follow the subshells like a ‘book’ across the periodic table. 1s 2 s p 3 4 d 5

3. Pauli Exclusion Principle:
SPDF rules
Pauli Exclusion Principle:
States that a maximum of two electrons may occupy a single atomic orbital, but only if the electrons have opposite spins

4. SPDF rules Hund’s Rule:
States that single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbitals.

5. Example
Hydrogen
1s1
1s 2s p .

6. Example
Oxygen
1s2 2s2 2p4
1s 2s p
Hund’s Rule: Fill all one direction First

7. Example
Carbon
1s2 2s2 2p2
1s 2s p
Hund’s Rule: Fill all one direction First

8. Write out the electronic configurations for the following elements:
Practice
Write out the electronic configurations for the following elements:
Nitrogen
Helium
Lithium
Sulfur
Chromium

9. Example
Nitrogen
1s22s22p3
1s 2s p .

10. Example
Helium
1s2
1s 2s p .

11. Example
Lithium
1s2 2s1
1s 2s p .

12. Example
Sulfur
1s22s22p63s23p4

13. Example
Chromium
1s22s22p63s23p64s23d4

14. [Noble gas element symbol] the rest of the electron configuration
Noble Gases Method
Shorthand notation
Since each element’s configuration builds on the previous elements’ configurations you can use the noble gases in brackets to save space
[Noble gas element symbol] the rest of the electron configuration

15. Noble Gases Method Example: Sulphur
We know it’s electron configuration is 1s22s22p63s23p4
Reading backwards, find the first noble gas (group 18) … Neon
Since neon’s electron configuration is 1s22s22p6
We can write sulfur as [Ne]3s23p4

16. Noble Gases Method Practice
Example: Zinc
Reading backwards, find the first noble gas (group 18) … Argon … [Ar]
Starting with group 1 one row (period) below the noble gas, write out the rest of the electronic configuration
We can write zinc as [Ar]4s23d10

17. Noble Gases Method Practice
Write out the electronic configurations using the Noble Gases Method for:
Rubidium
Chlorine
Silver
Magnesium

18. Noble Gases Method Practice
Rubidium [Kr]5s1
Chlorine [Ne]3s23p5
Silver [Kr]5s24d9
Magnesium [Ne]3s2

19. Example
Hydrogen
1s1 1s 2 s p 3 4 d 5

20. Principle Energy Level
Example
Hydrogen
1s1 1s 2 s p 3 4 d 5
Principle Energy Level
(n)

21. Principal energy levels n can be any of the numbers 1 to 7
We call this n
n can be any of the numbers 1 to 7
The first element in a period (row) begins a new principal energy level

22. Principal energy levels
Any number from 1 to 7 can be substituted for n
So if an element has valence electrons:
ns2np4
It can be 2s22p4, 3s23p4, 4s24p4, 5s25p4, 6s26p4, 7s27p4
What group are all of these elements found in?

23. Example
Hydrogen
1s1 1s 2 s p 3 4 d 5
Subshell

24. Example
Hydrogen
1s1 1s 2 s p 3 4 d 5
# electrons

25. Example
Lithium
1s2 2s1
# electrons = 3 1s 2 s p 3 4 d 5

26. Valence Electrons
Found in the outermost (the highest number) principal energy level (n)
n can be 1, 2, 3, 4, 5, 6, or 7
Always s & p electrons
Total number of electrons possible in s & p sublevels is 8
(max # electrons for s=2 and p=6) = 8
There can never be more than 8 valence electrons

27. Example
Boron
1s2 2s2 2p1
# electrons = 5 1s 2 s p 3 4 d 5

28. Example
Boron
1s2 2s2 2p1
# VALENCE electrons = 3 1s 2 s p 3 4 d 5

29. Electron configuration: 1s22s22p5 Fluorine has 7 valence electrons
Highest value of n: 2
Add total electrons found in s and p sublevels in principal energy level 2
2 + 5 = 7
Check: Is 7 less than 8? Yes
Fluorine has 7 valence electrons

30. Valence Electrons Phosphorus Electron configuration: 1s22s22p63s23p3
Highest value of n: 3
Add total electrons found in s and p sublevels in principal energy level 3
2 + 3 = 5
Check: Is 5 less than 8? Yes
Phosphorus has 5 valence electrons

31. Electron configurations of ions
Ion – an atom or molecule that has gained or lost one or more electrons and has a negative or positive charge
Cation – ion with a positive charge, it has lost one or more electrons
Anion – ion with a negative charge, it has gained one or more electrons

32. Electron configurations of ions
For cations (positive charge)…
The total number of electrons decreases by the charge: Atomic # - Charge
Ex: K+ (Charge=1+)
K has 19 electrons (atomic #)
K+ has 19-charge = 19-1 = 18 electrons

33. Electron configurations of ions
Ions change the electron configuration because they now have more or less electrons then an uncharged element
Ex: K+ has 18 electrons
[K] = 1s22s22p63s23p64s1
[K+] = 1s22s22p63s23p6
K+ has the same electron configuration as Argon – both have 18 electrons

34. Electron configurations of ions
For anions (negative charge)…
The total number of electrons increases by the charge: Atomic # + Charge
Ex: S2- (Charge=2-)
S has 16 electrons (atomic #)
S2- has 16+charge = 16+2 = 18 electrons

35. Electron configurations of ions
Ex: S2- has 18 electrons
[S] = 1s22s22p63s23p4
[S2-] = 1s22s22p63s23p6
S2- has the same electron configuration as Ar and K+ ... they all have 18 electrons