# Electron Rules

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```							Electron Rules

Unit 4 – The Electron
Electron Rules
 Where    do electrons go?

   There are 3 rules that govern…
Electron Rules
1.    Aufbau Principle
• Electrons enter the lowest possible
energy levels first
•   PEL 1 has the lowest E, then 2,etc
•     Then sublevels within a PEL
•   S is the lowest then p,d,f
•       Each orbital in a sublevel is equal
in E
Electron Rules
BUT 
 E- from very full PELs can spill into other
PELs
   Sometimes it takes less E to go to the next
PEL
Electron Rules
   Order of orbital filling – follow the arrow

1s
2s   2p
3s   3p    3d
4s   4p    4d   4f
5s   5p    5d   5f
6s   6p    6d   6f
7s   7p    7d   7f
Electron Rules
2. Pauli Exclusion
Principle
• Maximum of 2e- per
orbital
• Must have
opposite ‘spins’
Electron Rules
3. Hund’s Rule
• In orbitals of equal E, e- fill orbitals one-by-
one until they HAVE TO pair up!
•   Orbitals take 1 e- each with parallel spins,
before doubling up
•   Example:
2p with 2e-

With parallel spins as much as you
Can before pairing
Electron Rules
   Orbital Diagrams
   Visual representation of electron orbital
filling
   Examples:
   H

1s
Electron Rules
   Examples:
   He
1s

   Li
1s          2s

   C
1s          2s    2p
Electron Rules
   Electron Configurations
   Shorthand version of orbital diagrams

Principal                       # of e- in
Energy
1s2             sublevel
Level

Sublevel (orbital type)
Electron Rules
   Examples:
   H      1s1

   He     1s2

   Li     1s22s1

   C      1s22s22p2
Electron Rules
   Noble Gas Abbreviations
 Shorthand version of electron
configurations
 Example:
 Ne electron configuration
 1s22s22p6
 Na electron configuration:
 1s22s22p63s1
 Na with Noble Gas Abbreviation:
 [Ne] 3s1

```
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