Electron ConfigurationElectron Configuration

Na: 1Na: 1ss22 2 2ss22 2 2pp66 3 3ss11

Electron MovementElectron Movement

Electrons orbit the nucleus of an atom in Electrons orbit the nucleus of an atom in a cloud. a cloud.

Electrons do not orbit in a sphere neatly Electrons do not orbit in a sphere neatly around the nucleus, instead they tend to around the nucleus, instead they tend to migrate in different shapes around the migrate in different shapes around the nucleus.nucleus.

Electron configurations tells us in which orbitals Electron configurations tells us in which orbitals the electrons for an element are located.the electrons for an element are located.

Three rules:Three rules: electrons fill orbitals starting with lowest electrons fill orbitals starting with lowest

number and moving upwards;number and moving upwards; S-holds 2S-holds 2 P-holds 6P-holds 6 D- holds-10D- holds-10 F- holds 14 F- holds 14

Electron ConfigurationsElectron Configurations

Filling Diagram for SublevelsFilling Diagram for Sublevels

Electron ConfigurationsElectron Configurations The The electron configurationelectron configuration of an atom is a of an atom is a

shorthand method of writing the location of shorthand method of writing the location of electrons by sublevel.electrons by sublevel.

The sublevel is written followed by a superscript The sublevel is written followed by a superscript with the number of electrons in the sublevel.with the number of electrons in the sublevel.

If the 2If the 2pp sublevel contains 2 electrons, it is written 2 sublevel contains 2 electrons, it is written 2pp22

Writing Electron ConfigurationsWriting Electron Configurations First, determine how many electrons are in the First, determine how many electrons are in the

atom. Iron has 26 electrons.atom. Iron has 26 electrons. Arrange the energy sublevels according to Arrange the energy sublevels according to

increasing energy:increasing energy: 11ss 2 2ss 2 2pp 3 3ss 3 3pp 4 4ss 3 3dd ……

Fill each sublevel with electrons until you have Fill each sublevel with electrons until you have used all the electrons in the atom:used all the electrons in the atom:

Fe: 1Fe: 1ss22 2 2ss22 2 2pp66 3 3ss22 3 3pp66 4 4ss22 3 3dd 66

The sum of the superscripts equals the atomic The sum of the superscripts equals the atomic number of iron (26)number of iron (26)

PracticePractice

Write the electron configuration for Write the electron configuration for Fluorine:Fluorine:

1s1s222s2s222p2p55

What element has the electron What element has the electron configuration: 1sconfiguration: 1s222s2s222p2p663s3s22

MagnesiumMagnesium

• The periodic table can be used as a guide for electron configurations.

• The period number is the value of n.• Groups 1A and 2A have the s-orbital filled.• Groups 3A - 8A have the p-orbital filled.• Groups 3B - 2B have the d-orbital filled.• The lanthanides and actinides have the f-orbital filled.

Electron Configurations Electron Configurations and the Periodic Tableand the Periodic Table

Blocks and SublevelsBlocks and Sublevels We can use the periodic table to predict which We can use the periodic table to predict which

sublevel is being filled by a particular element.sublevel is being filled by a particular element.

Valence ElectronsValence Electrons When an atom undergoes a chemical reaction, When an atom undergoes a chemical reaction,

only the outermost electrons are involved.only the outermost electrons are involved.

These electrons are of the highest energy and are These electrons are of the highest energy and are furthest away from the nucleus. These are the furthest away from the nucleus. These are the valence electronsvalence electrons..

The valence electrons are the The valence electrons are the ss and and pp electrons electrons beyond the noble gas core.beyond the noble gas core.

Predicting Valence ElectronsPredicting Valence Electrons The Roman numeral in the American convention The Roman numeral in the American convention

indicates the number of valence electrons.indicates the number of valence electrons.

Group IA elements have 1 valence electronGroup IA elements have 1 valence electron

Group VA elements have 5 valence electronsGroup VA elements have 5 valence electrons

When using the IUPAC designations for group When using the IUPAC designations for group numbers, the last digit indicates the number of numbers, the last digit indicates the number of valence electrons.valence electrons.

Group 14 elements have 4 valence electronsGroup 14 elements have 4 valence electrons

Group 2 elements have 2 valence electronsGroup 2 elements have 2 valence electrons

Electron Dot FormulasElectron Dot Formulas An electron dot formula of an elements shows the An electron dot formula of an elements shows the

symbol of the element surrounded by its valence symbol of the element surrounded by its valence electrons.electrons.

We use one dot for each We use one dot for each valence electron.valence electron.

Consider phosphorous, P, which has 5 valence Consider phosphorous, P, which has 5 valence electrons. Here is the method for writing the electrons. Here is the method for writing the electron dot formula.electron dot formula.

Ionic ChargeIonic Charge Recall, that atoms Recall, that atoms lose or gain electrons lose or gain electrons to form to form

ions.ions.

The charge of an ion is related to the number of The charge of an ion is related to the number of valence electrons on the atom.valence electrons on the atom.

Group IA/1 metals lose their one valence electron Group IA/1 metals lose their one valence electron to form 1+ ions.to form 1+ ions.

Na Na → Na→ Na++ + e + e--

Metals lose their valence electrons to form ions.Metals lose their valence electrons to form ions.

Predicting Ionic ChargePredicting Ionic Charge Group IA/1 metals form 1+ ions, group IIA/2 Group IA/1 metals form 1+ ions, group IIA/2

metals form 2+ ions, group IIIA/13 metals form metals form 2+ ions, group IIIA/13 metals form 3+ ions, and group IVA/14 metals from 4+ ions.3+ ions, and group IVA/14 metals from 4+ ions.

By losing their valence electrons, they achieve a By losing their valence electrons, they achieve a noble gas configuration.noble gas configuration.

Similarly, nonmetals can gain electrons to achieve Similarly, nonmetals can gain electrons to achieve a noble gas configuration.a noble gas configuration.

Group VA/15 elements form -3 ions, group Group VA/15 elements form -3 ions, group VIA/16 elements form -2 ions, and group VIIA/17 VIA/16 elements form -2 ions, and group VIIA/17 elements form -1 ions.elements form -1 ions.

Ion Electron ConfigurationsIon Electron Configurations When we write the electron configuration of a When we write the electron configuration of a

positive ion, we remove one electron for each positive ion, we remove one electron for each positive charge:positive charge:

NaNa →→ Na Na++

11ss22 2 2ss22 2 2pp66 3 3ss1 1 →→ 11ss22 2 2ss22 2 2pp66

When we write the electron configuration of a When we write the electron configuration of a negative ion, we add one electron for each negative ion, we add one electron for each negative charge:negative charge:

OO →→ O O2-2-

11ss22 2 2ss22 2 2pp44 →→ 11ss22 2 2ss22 2 2pp66

Conclusions ContinuedConclusions Continued

We can Write the electron configuration of an We can Write the electron configuration of an element based on its position on the periodic element based on its position on the periodic table.table.

Valence electrons are the outermost electrons and Valence electrons are the outermost electrons and are involved in chemical reactions.are involved in chemical reactions.

We can write electron dot formulas for elements We can write electron dot formulas for elements which indicate the number of valence electrons.which indicate the number of valence electrons.

Conclusions ContinuedConclusions Continued We can predict the charge on the ion of an We can predict the charge on the ion of an

element from its position on the periodic table.element from its position on the periodic table.