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 OOrbital Diagrams VVisual representation of electron orbital filling EExamples: HH 1s

 Examples:  He  Li CC 1s 2s 2p 1s

Electron Rules  Electron Configurations  Shorthand version of orbital diagrams 1s 2 Principal Energy Level Sublevel (orbital type) # of e - in sublevel

Electron Rules  Examples:  H1s 1  He1s 2  Li1s 2 2s 1  C1s 2 2s 2 2p 2

Electron Rules  Noble Gas Abbreviations  Shorthand version of electron configurations  Example:  Ne electron configuration  1s 2 2s 2 2p 6  Na electron configuration:  1s 2 2s 2 2p 6 3s 1  Na with Noble Gas Abbreviation:  [Ne] 3s 1