Electron ConfigurationsElectron Configurations

Chapter 5Chapter 5

Section 3Section 3

VocabularyVocabulary

electron configurationelectron configuration

aufbau principleaufbau principle

Pauli exclusion principlePauli exclusion principle

Hund’s ruleHund’s rule

Valence electronValence electron

Electron-dot structure Electron-dot structure

ReviewReview

Each principal energy level can have the Each principal energy level can have the same number of sublevels as the level same number of sublevels as the level numbernumber

Each sublevel orbital has a different shapeEach sublevel orbital has a different shape

Each orbital can have only 2 electronsEach orbital can have only 2 electrons

What does this mean?What does this mean?

Electron Arraignment follows Electron Arraignment follows RulesRules

Low energy level systems are more stable than Low energy level systems are more stable than high-energy systemshigh-energy systems Atoms will assume the electron arrangement that Atoms will assume the electron arrangement that

gives the atom the lowest energygives the atom the lowest energy Most stable is the “ground state” (lowest energy)Most stable is the “ground state” (lowest energy)

Three rules/principles for arranging electronsThree rules/principles for arranging electrons AufbauAufbau Pauli Exclusion principlePauli Exclusion principle Hund’s RuleHund’s Rule

Aufbau PrincipleAufbau Principle

Each electron occupies the lowest energy Each electron occupies the lowest energy level availablelevel available Learn the sequence of atomic orbitals from Learn the sequence of atomic orbitals from

lowest to highest:lowest to highest:

Aufbau DiagramAufbau Diagram

#4 – also do electron DOT diagram, #7 & 8 – SHOW YOUR WORK

Aufbau ExpandedAufbau Expanded

Using AufbauUsing AufbauAll orbitals related to the same energy level are of All orbitals related to the same energy level are of equal energyequal energy All 2p orbitals have the same energyAll 2p orbitals have the same energy

In a multi-electron atom, the energy sublevels within a In a multi-electron atom, the energy sublevels within a principal energy level have different energies:principal energy level have different energies: 2p orbitals are higher energy than 2s orbitals2p orbitals are higher energy than 2s orbitals

The sequence of sublevels within a principle level in The sequence of sublevels within a principle level in increasing energy is: s, p, d, and fincreasing energy is: s, p, d, and fOrbitals related to energy sublevels within one Orbitals related to energy sublevels within one principle energy level can overlap orbitals related to principle energy level can overlap orbitals related to another principal levelanother principal level Notice: 4s is lower than 3dNotice: 4s is lower than 3d

Pauli Exclusion PrinciplePauli Exclusion Principle

Each electron has an associated spin, like Each electron has an associated spin, like a topa top Can spin on bottom or topCan spin on bottom or top

Each orbital can hold AT MOST 2 Each orbital can hold AT MOST 2 electrons, but only if they have opposite electrons, but only if they have opposite spinspin Designated as:Designated as:

Hund’s RuleHund’s Rule

Because negatively charged electrons Because negatively charged electrons repel each other, they try to get as far repel each other, they try to get as far away from each other as possible, away from each other as possible, therefore:therefore:Single electrons with the same spin will Single electrons with the same spin will occupy each equal energy orbital occupy each equal energy orbital before before additional electrons with opposite spins additional electrons with opposite spins occupy the same orbitals.occupy the same orbitals.WHAT? WHAT?

Hund’s RuleHund’s Rule

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4

Representing Atom’s ElectronsRepresenting Atom’s Electrons

1.1. Orbital DiagramsOrbital Diagrams

2.2. Electron Configuration NotationsElectron Configuration Notations

Orbital DiagramsOrbital Diagrams

Draw one box for each orbitalDraw one box for each orbital Empty box means no electronsEmpty box means no electrons Box with single up arrow means orbital with Box with single up arrow means orbital with

one electronone electron Box with two arrows (up/down) means orbital Box with two arrows (up/down) means orbital

with two electronswith two electrons Each box is labeled with the principle Each box is labeled with the principle

quantum number and the sublevelquantum number and the sublevel

Example:Example:

Example Orbital Diagram - N Example Orbital Diagram - N

Example Orbital Diagram – C & OExample Orbital Diagram – C & O

Electron Configuration NotationElectron Configuration Notation

Specify principal energy level and energy Specify principal energy level and energy sublevelsublevel

Use a superscript to represent the number Use a superscript to represent the number of electronsof electrons Use the Aufbau diagram to help you Use the Aufbau diagram to help you

remember the level/sublevel filling orderremember the level/sublevel filling order

Examples:Examples:

Electron Configuration NotationElectron Configuration Notation

Electron Configuration NotationElectron Configuration Notation

ElementElement ECNECN ElementElement ECNECN

HydrogenHydrogen 1s1s11 CarbonCarbon 1s1s2 2 2s2s2 2 2p2p22

HeliumHelium 1s1s22 NitrogenNitrogen 1s1s2 2 2s2s2 2 2p2p33

LithiumLithium 1s1s2 2 2s2s11 OxygenOxygen 1s1s2 2 2s2s2 2 2p2p44

BerylliumBeryllium 1s1s22 2s 2s22 FluorineFluorine 1s1s2 2 2s2s2 2 2p2p55

BoronBoron 1s1s2 2 2s2s22 2p 2p11 neonneon 1s1s2 2 2s2s2 2 2p2p66

A Variation – Noble Gas A Variation – Noble Gas NotationNotation

Similar to Electron Configuration Notation, Similar to Electron Configuration Notation, but:but: Start with the previous noble gas, and put that Start with the previous noble gas, and put that

symbol in bracketssymbol in brackets Add electrons to the noble gasAdd electrons to the noble gas

Example:Example:Sodium (Na) = [Ne] 3sSodium (Na) = [Ne] 3s11

Ne = 1sNe = 1s22 2s 2s22 2p 2p66

Na = 1sNa = 1s22 2s 2s22 2p 2p66 3s 3s11

Exceptions to AufbauExceptions to Aufbau

Cr (Chromium) = [Ar] 4sCr (Chromium) = [Ar] 4s11 3d 3d55

Cu (Copper) = [Ar] 4sCu (Copper) = [Ar] 4s11 3d 3d1010

Valence ElectronsValence Electrons

Only Valence Electrons contribute to Only Valence Electrons contribute to chemical bondingchemical bonding

Valence Electrons = electrons in outer Valence Electrons = electrons in outer most most principal energy levelprincipal energy level Generally highest energyGenerally highest energy

Examples:Examples: Carbon: [He] 2sCarbon: [He] 2s2 2 2p2p22 has 4 valence electrons has 4 valence electrons Sulfur: [Ne] 3sSulfur: [Ne] 3s22 3p 3p44 has 6 valence electrons has 6 valence electrons

Electron Dot DiagramsElectron Dot Diagrams

Also called Lewis Electron Dot Diagrams Also called Lewis Electron Dot Diagrams or Lewis Electron Dot Structure or Electron or Lewis Electron Dot Structure or Electron Dot StructureDot Structure

Shows atomic symbol and ONLY valence Shows atomic symbol and ONLY valence electronselectrons

Electron Dot DiagramsElectron Dot Diagrams

Periodic TablePeriodic Table