Chemistry Notes Electron Configurations. Studying the arrangement of electrons in atoms helps one understand chemical activity. From an electron configuration

Chemistry NotesChemistry Notes

Electron ConfigurationsElectron Configurations

Electron Configurations Electron Configurations

Studying the arrangement of electrons Studying the arrangement of electrons in atoms helps one understand in atoms helps one understand chemical activity.chemical activity.

From an electron configuration you can From an electron configuration you can determine:determine: Most stable electron arrangement Most stable electron arrangement ChargeCharge Bonding patternsBonding patterns Etc.Etc.


Electron Configurations:Electron Configurations: Shows the Shows the Principle Energy Levels, the sublevels and Principle Energy Levels, the sublevels and the number of electrons in those the number of electrons in those sublevels.sublevels.

Examples of electron configurations:Examples of electron configurations:H H 1s 1s11

He He 1s 1s22

Li Li 1s 1s222s2s11

O O 1s 1s222s2s222p2p44



Rule to remember when writing an Rule to remember when writing an electron configuration for a certain atom:electron configuration for a certain atom:

Auf Bau PrincipleAuf Bau Principle – – The lowest energy The lowest energy levels fill first in atomslevels fill first in atoms Some Energy Levels do overlapSome Energy Levels do overlap

In atoms a In atoms a 4s 4s level will fill before a level will fill before a 3d3d level level because the because the 4s4s sublevel has a sublevel has a lower energylower energy than the than the 3d3d..


Notice: the 4s is lower in energy than the Notice: the 4s is lower in energy than the 3d sublevel, therefore, it fills first.3d sublevel, therefore, it fills first.

Electron ConfigurationsElectron ConfigurationsStart at the top of the arrow, go down. Once you are at the head of the arrow go to the top of the next. Repeat until you have reached the desired number of electrons.

Using this diagram can help you understand how to write the correct electron configuration for each atom.

Electron ConfigurationsElectron ConfigurationsEX: Ag has 47 electronsEX: Ag has 47 electrons

Fill sublevels unit they add up to 47.Remember how many electrons can go in each sublevel.

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d9

s = 2

p = 6

d = 10

f = 14

Notice: the last sublevel only contains 9 (not 10) electrons


Another Ex: Another Ex: Titanium has 22 electrons

Ti: 1s2 2s2 2p6 3s2 3p6 4s2 3d2

2 6 10 14


Here is a similar diagram for ECHere is a similar diagram for EC


EC can be abbreviated EC can be abbreviated a noble a noble gas configuration (seen below).gas configuration (seen below).

Element ZElectron

Configuration

Noble Gas Configuration

Scandium 211s2 2s2 2p6 3s2 3p6 4s2

3d1

[Ar] 4s2 3d1

Titanium 221s2 2s2 2p6 3s2 3p6 4s2

3d2

[Ar] 4s2 3d2

Vanadium 231s2 2s2 2p6 3s2 3p6 4s2

3d3

[Ar] 4s2 3d3Notice: [Ar] represents the EC of Argon

Orbital Filling DiagramsOrbital Filling DiagramsAn orbital diagram give more detailed An orbital diagram give more detailed information than an electron configuration.information than an electron configuration.

Boxes or blanks are used to represent Boxes or blanks are used to represent orbitals.orbitals.

Arrows represent electrons.Arrows represent electrons. Upward-pointing arrows represent electrons with +1/2 spinUpward-pointing arrows represent electrons with +1/2 spin Downward-pointing arrows represent electrons with -1/2 spinDownward-pointing arrows represent electrons with -1/2 spin

Like EC but arrows are used instead of #’sLike EC but arrows are used instead of #’s

Orbital Filling DiagramsOrbital Filling Diagrams


Rules to remember when writing an Rules to remember when writing an orbital filling diagram for a certain orbital filling diagram for a certain atom:atom:

Hund’s Rule – each orbital gets one electron before any get two EX: Nitrogen each 2p orbital gets on e-

before any get 2 e-.


Hund’s Rule (cont.)Hund’s Rule (cont.)

Notice that the 2p electrons are shown as… Notice that the 2p electrons are shown as…

rather than. rather than.

This is WRONG!!!


Rules to remember when writing an Rules to remember when writing an orbital filling diagram for a certain orbital filling diagram for a certain atom:atom:

Pauli Exclusion PrinciplePauli Exclusion Principle – electrons in – electrons in the same orbital must spin opposite the same orbital must spin opposite directions.directions. This is why one arrow is This is why one arrow is drawn updrawn up and one is and one is

drawn downdrawn down..

Orbital Filling DiagramsOrbital Filling DiagramsExamples of An Orbital Filling DiagramsExamples of An Orbital Filling Diagrams

OFD and ECOFD and EC

SummarySummary

Be able to…Be able to…

Explain what EC and OFD areExplain what EC and OFD are

Write and ECWrite and EC Recall the Auf Bau PrincipleRecall the Auf Bau Principle

Write and OFDWrite and OFD Recall Hund’s Rule Recall Hund’s Rule Recall the Pauli Exclusion PrincipleRecall the Pauli Exclusion Principle

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Chemistry Notes Electron Configurations. Studying the arrangement of electrons in atoms helps one understand chemical activity. From an electron configuration