1. Electron Configuration
The way in which electrons are arranged around the nuclei of atoms

2. General Rules Pauli Exclusion Principle
Each orbital can hold TWO electrons with opposite spins
Aufbau Principle
Electrons fill the lowest energy orbitals first.
“Lazy Tenant Rule”

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

4. Orbitals fill in an order
Lowest energy to higher energy.
Adding electrons can change the energy of the orbital.
Full orbitals are the absolute best situation.
However, half filled orbitals have a lower energy, and are next best
Makes them more stable.
Changes the filling order

5. 1s2 2s2 2p4 O Notation 1s 2s 2p 8e- Orbital Diagram
Electron Configuration 1s 2s 2p O
8e-
1s2 2s2 2p4

6. S 16e- 1s2 2s2 2p6 3s2 3p4 S 16e- [Ne] 3s2 3p4 Notation Core Electrons
Longhand Configuration
Shorthand Configuration
S 16e-
1s2
2s2
2p6
3s2
3p4
Core Electrons
Valence Electrons
S 16e- [Ne] 3s2 3p4

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

8. Periodic Patterns Period # A/B Group # Column within sublevel block
energy level (subtract for d & f)
A/B Group #
total # of valence e-
Column within sublevel block
# of e- in sublevel

9. Periodic Patterns p s d (n-1) f (n-2) Shorthand Configuration
Core e-: Go up one row and over to the Noble Gas.
Valence e-: On the next row, fill in the # of e- in each sublevel. s
d (n-1)
f (n-2) p

10. Periodic Patterns
Example - Germanium
[Ar]
4s2
3d10
4p2

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

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

13. Stability O2- 10e- [He] 2s2 2p6 Ion Electron Configuration
Write the e- config for the closest Noble Gas
EX: Oxygen ion  O2-  Ne
O e [He] 2s2 2p6