Untitled Flashcard Set

The Aufbau Principle

Each electron occupiesEach electron occupies

the lowest energythe lowest energy

orbitalorbital

 Electrons are Lazy!!!Electrons are Lazy!!!

All orbitals related to anAll orbitals related to an

energy level are ofenergy level are of

equal energy.equal energy.

 Ex. The three 2p orbitalsEx. The three 2p orbitals

are the same energyare the same energ

Pauli Exclusion Principle

A maximum of twoA maximum of two

electrons may occupy aelectrons may occupy a

single orbital, butsingle orbital, but only ifonly if

the electrons havethe electrons have

opposite spins.opposite spins.

 Spin -- Electrons has anSpin -- Electrons has an

associated “spin,” either oneassociated “spin,” either one

way or the other, like a top.way or the other, like a top.

 These spins are called “spinThese spins are called “spin

up” and “spin down.”up” and “spin down.”

 See example on board.See example on board.

Box = orbital

Arrow = electron

Hund’s Rule

Single electrons with theSingle electrons with the

samesame spin must occupyspin must occupy

each equal-energyeach equal-energy

orbitalorbital beforebefore additionaladditional

electrons with oppositeelectrons with opposite

spins can occupy thespins can occupy the

samesame orbitals.orbitals.

 Electrons areElectrons are

UNFRIENDLYUNFRIENDLY

 Why?Why?

1s2 2s2 2p3

NOT

Ex. Nitrogen:

•1s2 2s2 2p3