Electron Rules

							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
         •     Start with PEL
              •   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-

     Spread the electrons out
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