Bell WorkBell WorkPrinciple Energy Level

Sublevel(s)

Orbital(s) # of electrons

n=1 1s 1s- one orbital

1s- 2 electrons

Electron Electron ConfigurationsConfigurations

Electron ConfigurationElectron Configuration

- distribution of - distribution of electrons among electrons among the orbital's of an the orbital's of an atomatom

Electron Configurations Electron Configurations are determined by: are determined by:

distributing the atom’s electrons among:distributing the atom’s electrons among:

(Using a set of stated

principles)

---levels---sublevels---orbitals

Ground StateGround Stateelectrons occupy lowest energy electrons occupy lowest energy

orbitals available to themorbitals available to themmost stable, lowest energy most stable, lowest energy

state of an atomstate of an atomThis is how e’s normally existThis is how e’s normally exist

Three Principles for Three Principles for Electron ConfigurationsElectron Configurations

1. 1. Aufbau PrincipleAufbau Principle – – electrons added 1 at a electrons added 1 at a time to time to lowestlowest energy energy orbital availableorbital available

2. 2. Pauli Exclusion Pauli Exclusion PrinciplePrinciple – – An orbital An orbital can hold a maximum of 2 can hold a maximum of 2 electrons and they must electrons and they must have opposite spins.have opposite spins.

3.3. Hund’s RuleHund’s Rule – – Electrons will occupy Electrons will occupy equal-energy orbitals so equal-energy orbitals so that a maximum number that a maximum number of unpaired electrons of unpaired electrons resultsresults

Ex: 2p orbitalsEx: 2p orbitals

Orbital DiagramOrbital Diagram

---shows the locations ---shows the locations of the e’s according of the e’s according to the 3 principlesto the 3 principles

Orbital DiagramsOrbital Diagrams

FeFe

How many electrons do we need?

ENERGY

1s

2s 2p

3s3p

4s3d

CaCa

How many electrons do we need?

ENERGY

1s

2s2p

3s3p

4s

BeBe

How many electrons do we need?

ENERGY

1s

2s

MgMg

How many electrons do we need?

ENERGY

1s

2s2p

3s

PP

How many electrons do we need?

ENERGY

1s

2s2p

3s3p

How to write an electron How to write an electron configurationconfiguration

1.1. Determine # of electrons in atom Determine # of electrons in atom or ionor ion

2.2. Using arrow chart, start placing Using arrow chart, start placing electrons in the lowest energy electrons in the lowest energy sublevels (remember the rules)sublevels (remember the rules)

REMEMBER….REMEMBER….S’s – only 2 electronsS’s – only 2 electrons

P’s – only 6 electronsP’s – only 6 electrons

D’s – only 10 D’s – only 10 electronselectrons

F’s – only 14 electronsF’s – only 14 electrons

PracticePractice

1.1. CarbonCarbon

2.2. ArgonArgon

3.3. MnMn

4.4. RadonRadon

How to do an abbr. How to do an abbr. electron conf:electron conf:

1.1. Determine the number of Determine the number of electronselectrons

2.2. Find the noble gas (last Find the noble gas (last column) that is closest to your column) that is closest to your element element butbut that has less that has less electronselectrons

3.3. Write the symbol for that Write the symbol for that noble gas in square noble gas in square brackets (ex: [Ne])brackets (ex: [Ne])

4.4. After the [ ] continue the After the [ ] continue the configuration like normalconfiguration like normal

C 1sC 1s222s2s222p2p22..

Na 1sNa 1s222s2s222p2p663s3s11..

P 1sP 1s222s2s222p2p663s3s223p3p33..

Br 1sBr 1s222s2s222p2p663s3s223p3p664s4s223d3d10104p4p55..

Cd 1sCd 1s222s2s222p2p663s3s223p3p664s4s223d3d10104p4p665s5s224d4d1010..

Abbreviated Electron Configuration

Use the noble gas from the row above your element then add the rest of the configuration

[He]

[Ne]

[Ne]

[Ar]

[Kr]

Arrow ChartArrow Chart