1. Electron Configurations

2. Rules for Housing Electrons
Aufbau Principle: an electron occupies the lowest possible energy orbital
(see filling chart)
Hund’s Rule
Orbitals of equal energy are occupied by 1e- before any one orbital is occupied by a 2nd e-
All e- ’s in singly occupied orbitals must have the same spin

3. (it’s like an address for finding the e-)
Housing Rules
Pauli Exclusion Principle: no two e- ’s in the same atom can have the same set of 4 quantum numbers
(it’s like an address for finding the e-)

4. Drawing Orbital Diagrams
Each orbital is represented by a box or line
These can be vertical—top to bottom
-OR- These can be horizontal –left to right
1 e- goes in each orbital ↑ or ↓
2 e- possible in each orbital ↑↓
Lines are labeled with principle quantum number and subshell letter (s,p,d,f…)

5. Filling Diagram Why do we fill this way?!? … 1s 2s 3s 4s 5s 6s 7s 8s2p 3p 4p 5p 6p 7p 3d 4d 5d 6d 4f 5f
Filling Diagram
Why do we fill this way?!? …

6. Relative Energies of Orbitals

7. Your Turn!
Helium He:
Silicon Si:

8. Writing Electron Configurations
Eliminates arrows and lines from orbital notation
A superscript is written on the sublevel letter to indicate the number of e- ’s
Electrons enter lowest energy orbitals first (see filling chart)

9. Your Turn!
He: 1s (2 e- ’s)
Si: 1s22s22p63s23p2 (14 e- ’s)
Ge:
Mg+2 :

10. Patterns in the Periodic Table

11. Patterns in the Periodic Table: s
 The first two columns in the P.T. (and He) are known as the “s” block

12. Patterns in the Periodic Table: p
 Elements 5-10 and all of the elements underneath that row are known as the “p” block This block has 6 columns.

13. Patterns in the Periodic Table: d
Elements and all of the elements underneath that row are known as the “d” block. This block has 10 columns.

14. Patterns in the Periodic Table: f
 The bottom two rows in the P.T. are known as the f block. This block has 14 columns.

15. Valence Electrons
Valence electrons are the outermost electrons of an atom from the s and p orbitals
Atoms with a complete shell of valence electrons (s2p6) are considered chemically inert

16. Electron Configurations
Noble Gas Shorthand
For elements with completely filled shells
Substitute [noble gas] for electron configuration notation
Example:
Si: 1s22s22p63s23p2 can be written [Ne]3s23p2

17. Valence Electrons
For most elements, valence electrons can be defined as those in the electronic shell of highest principle NRG level (n)
Ex. the electron configuration of phosphorus (P) is 1s2 2s2 2p6 3s2 3p3 so that are 5 valence electrons (3s2 3p3),

18. Valence Electrons

19. Electron Dot Diagram Shows the number of valence electrons
The first column of the Periodic Table have electron configurations that end in s1 so they have one valence electron.

20. Electron Dot Diagram
The second column of the Periodic Table (and He) have electron configurations that end in s2 so they have two valence electrons.

21. Electron Dot Diagram
The column starting with Boron has electron configurations that end in s2 p1 so they have three valence electrons.

22. Electron Dot Diagram
The column starting with Carbon has electron configurations that end in s2 p2 so they have four valence electrons.

23. Electron Dot Diagram
The column starting with Nitrogen has electron configurations that end in s2 p3 so they have five valence electrons.
And the pattern continues…

24. Electron Dot Diagram

25. Electron Configurations
Exceptions (rows 4 & 5 of P.T.)
Half filled orbitals have special stability (all electrons have the same spin)
Cr: [Ar] 4s13d5 NOT… [Ar]4s23d4
Filled orbitals have special stability
Pd: [Kr] 4d NOT… [Kr] 4d85s2