Electron Rules

Unit 4 – The Electron

Electron Rules

Where do electrons go?

There are 3 rules that govern…

Electron Rules1. 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

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

Electron Rules

2. Pauli Exclusion Principle

• Maximum of 2e- per orbital• Must have

opposite ‘spins’

Electron Rules3. 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 outWith 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

Li

C

1s

1s 2s

2s 2p1s

Electron Rules

Electron Configurations Shorthand version of orbital diagrams

1s2Principal Energy Level

Sublevel (orbital type)

# of e- in sublevel

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