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2.12.1 Elements and Elements and SymbolsSymbols

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Elements are pure substances that cannot Elements are pure substances that cannot be separated into simpler substances by be separated into simpler substances by ordinary laboratory processes.ordinary laboratory processes.

Elements are the building blocks of Elements are the building blocks of matter.matter.

There are 113 elements known today. There are 113 elements known today.

gold gold carbon aluminum carbon aluminum

ElementsElements

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Sources of Some Element Sources of Some Element NamesNames

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Every element has a symbol that Every element has a symbol that represents its name.represents its name.

Symbols consist of 1 or 2 letters. Symbols consist of 1 or 2 letters. Only the first letter in a symbol is Only the first letter in a symbol is

capitalized.capitalized.Examples:Examples:1-Letter Symbols 1-Letter Symbols 2-Letter Symbols2-Letter Symbols

C carbon C carbon Co Co cobaltcobalt

N nitrogenN nitrogen Ca Ca calciumcalciumF fluorine F fluorine Al Al aluminumaluminumO oxygen O oxygen Mg Mg

magnesiummagnesium

Symbols of ElementsSymbols of Elements

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Several symbols are derived from Latin Several symbols are derived from Latin names.names.

Some examples are shown below:Some examples are shown below:

copper, Cu (cuprum)copper, Cu (cuprum) gold, Au (aurum) gold, Au (aurum)

iron, Fe (ferrum)iron, Fe (ferrum) silver, Ag (argentum) silver, Ag (argentum)

Symbols from Latin NamesSymbols from Latin Names

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Carbon, oxygen, and hydrogen are the most Carbon, oxygen, and hydrogen are the most abundant elements in the human body. abundant elements in the human body.

Elements in the BodyElements in the Body

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The physical The physical properties of properties of an element are an element are the the characteristics characteristics that can be that can be observed observed without without changing the changing the substance. substance.

Physical PropertiesPhysical Properties

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2.22.2 The Periodic TableThe Periodic Table

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The The periodic periodic table table arranges arranges elements elements according according to similar to similar propertiesproperties..

Periodic TablePeriodic Table

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On the periodic table, each vertical On the periodic table, each vertical column is called a column is called a groupgroup of elements.of elements.

A A groupgroup contains elements with contains elements with similar chemical and physical similar chemical and physical properties.properties.

Each group is identified by a group Each group is identified by a group number at the top of the column.number at the top of the column.

The The representative elementsrepresentative elements have have group numbers of 1A – 8A. The group numbers of 1A – 8A. The transition elementstransition elements use the letter “B.”use the letter “B.”

Groups on the Periodic Groups on the Periodic TableTable

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Groups and Group NumbersGroups and Group Numbers

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Numbering GroupsNumbering Groups

One numbering system for groups One numbering system for groups assigns the letter A to the assigns the letter A to the representative elements and the representative elements and the letter B to the transition elements.letter B to the transition elements.

Another system assigns the Another system assigns the numbers 1-18 to the columns numbers 1-18 to the columns across the periodic table.across the periodic table.

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Group NumbersGroup Numbers

Group numbers

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Several groups of representative Several groups of representative elements are classified by name.elements are classified by name.

Group 1AGroup 1A Alkali MetalsAlkali MetalsGroup 2AGroup 2A Alkaline Earth MetalsAlkaline Earth MetalsGroup 7A Group 7A HalogensHalogensGroup 8AGroup 8A Noble GasesNoble Gases

Representative ElementsRepresentative Elements

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Names of Some Representative Names of Some Representative GroupsGroups

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Group 1A, theGroup 1A, thealkali metalsalkali metals,, includes includes sodium, lithium, sodium, lithium, and potassium.and potassium.

Group 7A, the Group 7A, the halogenshalogens, , includes includes chlorine, chlorine, bromine, bromine, and iodine.and iodine.

Representative ElementsRepresentative Elements

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On the periodic table, each On the periodic table, each horizontal row is called a horizontal row is called a periodperiod. .

A period is identified by a number A period is identified by a number such as 1, 2, 3, or 4. such as 1, 2, 3, or 4.

Periods 2-7 include representative Periods 2-7 include representative elements and transition elements.elements and transition elements.

Periods on the Periodic Periods on the Periodic TableTable

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Location of PeriodsLocation of Periods

Period 4

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NONMETALS

METALOIDS

Metals, Nonmetals, and Metals, Nonmetals, and MetalloidsMetalloids

METALS

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MetalsMetals Are located to the left of the heavy line. Are located to the left of the heavy line. Are shiny, ductile, and good conductors.Are shiny, ductile, and good conductors.

MetalloidsMetalloids Are elements along the heavy line.Are elements along the heavy line. Have properties of both metals and Have properties of both metals and

nonmetalsnonmetals.. NonmetalsNonmetals

Are located to the right of the heavy line.Are located to the right of the heavy line. Are dull, brittle, poor conductors, and good Are dull, brittle, poor conductors, and good

insulators.insulators.

Metals and NonmetalsMetals and Nonmetals

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Comparing A Metal, Comparing A Metal, Metalloid, and NonmetalMetalloid, and Nonmetal

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2.3 The Atom2.3 The Atom

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Matter is composed of tiny particles Matter is composed of tiny particles called atoms. called atoms.

Atoms in each element are similar and Atoms in each element are similar and different from atoms of other elements.different from atoms of other elements.

Atoms of two or more different Atoms of two or more different elements combine in simple ratios to elements combine in simple ratios to form compounds.form compounds.

A chemical reaction involves changes in A chemical reaction involves changes in the arrangements of atoms.the arrangements of atoms.

Atomic TheoryAtomic Theory

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Subatomic ParticlesSubatomic Particles

Chemists are Chemists are interested in three interested in three particles in atoms:particles in atoms: protons, electrons, protons, electrons, and neutronsand neutrons..

Protons have a Protons have a positive (+) charge; positive (+) charge; electrons have a electrons have a negative (-) charge.negative (-) charge.

Like charges repel Like charges repel and unlike charges and unlike charges attract.attract.

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Summary of Subatomic Summary of Subatomic ParticlesParticles

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Rutherford’s Gold-Foil Rutherford’s Gold-Foil ExperimentExperiment

Most positive particles aimed at atoms of Most positive particles aimed at atoms of gold went straight through the atoms. Only gold went straight through the atoms. Only a few were deflected.a few were deflected.

Rutherford concluded that atoms have a Rutherford concluded that atoms have a small, dense nucleus with a positive charge.small, dense nucleus with a positive charge.

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An atom consists of An atom consists of a nucleus and a a nucleus and a cloud of electrons.cloud of electrons.

The nucleus The nucleus contains all of the contains all of the protons and protons and neutrons.neutrons.

The rest of the The rest of the atom, which is atom, which is mostly empty space, mostly empty space, is occupied by the is occupied by the electrons.electrons.

Structure of the AtomStructure of the Atom

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The The atomic number atomic number is equal to the is equal to the number of protons in an atom.number of protons in an atom.

On the periodic chart, the atomic On the periodic chart, the atomic number appears above the symbol of number appears above the symbol of an element.an element.

2.4 Atomic Number and 2.4 Atomic Number and Mass NumberMass Number

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Na

Atomic Number

Symbol

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Atomic Numbers and Atomic Numbers and Protons for Lithium and Protons for Lithium and

Carbon AtomsCarbon Atoms

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An atom is electrically neutral; the net An atom is electrically neutral; the net charge is zero.charge is zero.

In an atom, the number of protons is In an atom, the number of protons is equal to the number of electrons. equal to the number of electrons.

# protons = # electrons# protons = # electrons Therefore, the Therefore, the atomic numberatomic number is also is also

equal to the number of electrons in a equal to the number of electrons in a neutral atom.neutral atom.

Electrons in An AtomElectrons in An Atom

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The The mass numbermass number gives the total number of gives the total number of protons and neutrons in the nucleus.protons and neutrons in the nucleus. Mass number = # protons + # Mass number = # protons + # neutronsneutrons

Mass NumberMass Number

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The atomic symbol represents a The atomic symbol represents a particular atom of an element.particular atom of an element.

The atomic symbol shows the The atomic symbol shows the mass mass numbernumber in the upper left cornerin the upper left corner and the and the atomic numberatomic number in the in the lower left corner.lower left corner.

For example, an atom of sodium with For example, an atom of sodium with atomic number 11 and a mass number atomic number 11 and a mass number 23 has the following atomic symbol:23 has the following atomic symbol:

mass numbermass number 23 23 Na Na atomic numberatomic number 1111

Atomic SymbolAtomic Symbol

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When we know the atomic symbol of When we know the atomic symbol of an atom, we can determine the an atom, we can determine the number of protons (pnumber of protons (p++), neutrons, ), neutrons, (n), and electrons (e(n), and electrons (e--).).1616 3131 6565

OO P P Zn Zn 88 1515 3030

8 p8 p++ 15 p15 p++ 30 p30 p++

8 n8 n 16 n16 n 35 n35 n8 e8 e-- 1515 ee-- 30 e30 e--

Information from Atomic Information from Atomic SymbolsSymbols

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2.5 Isotopes and Atomic 2.5 Isotopes and Atomic MassMass

24Mg 25Mg 26Mg 12 12 12

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IsotopesIsotopes are atoms of the same element are atoms of the same element that have different mass numbers.that have different mass numbers.

Isotopes have the Isotopes have the same number of same number of protonsprotons, but , but different numbers of different numbers of neutronsneutrons. .

Most elements have two or more isotopes.Most elements have two or more isotopes.

IsotopesIsotopes

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Isotopes of MagnesiumIsotopes of Magnesium

In naturally In naturally occurring atoms of occurring atoms of magnesium, there magnesium, there are three isotopes.are three isotopes.

2424Mg makes up 78.9% Mg makes up 78.9% of magnesium atoms.of magnesium atoms.

2525Mg makes up 10.0% Mg makes up 10.0% and and 2626Mg makes up Mg makes up 11.1%. 11.1%.

24Mg 25Mg 26Mg 12 12 12

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Atomic mass is the Atomic mass is the weighted average weighted average massmass of all the isotopes of that element. of all the isotopes of that element.

The atomic mass of each element is The atomic mass of each element is compared to compared to 1212C, which a mass of 12 amu. C, which a mass of 12 amu.

The atomic mass of each element is listed The atomic mass of each element is listed below the symbol of the element on the below the symbol of the element on the periodic table.periodic table.

Atomic MassAtomic Mass

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Atomic Mass of MagnesiumAtomic Mass of Magnesium

The individual The individual atomic masses of atomic masses of all the isotopes all the isotopes contribute to the contribute to the atomic mass of atomic mass of Mg.Mg.

As a weighted As a weighted average, the average, the atomic mass is not atomic mass is not a whole number.a whole number.

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To calculate atomic mass, use the To calculate atomic mass, use the percent(%) abundancepercent(%) abundance of the isotopes of the isotopes and the and the massmass of each isotope of that of each isotope of that element.element.

mass isotope(1) x (%)mass isotope(1) x (%) + + mass isotope mass isotope (2) x (%)(2) x (%) + … + …

100 100 100 100

Calculating Atomic MassCalculating Atomic Mass

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Atomic Mass for ClAtomic Mass for Cl

The atomic The atomic mass of mass of chlorine is chlorine is the the weighted weighted average of average of two isotopes two isotopes 3535Cl and Cl and 3737Cl.Cl.

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Cl-35 is 75.8 %Cl-35 is 75.8 % and and Cl-37 is 24.2%Cl-37 is 24.2% of of natural chlorine. natural chlorine.

Using the given atomic mass of each Using the given atomic mass of each isotope, calculate the contribution of isotope, calculate the contribution of each isotope to the atomic mass of Cl.each isotope to the atomic mass of Cl.35.0 x 35.0 x 75.8 75.8 = = 26.526.5

100 10037.0 x 37.0 x 24.2 24.2 = = 8.958.95

100 100 Add togetherAdd together = = 35.4535.45 = =

atomic mass Clatomic mass Cl

Calculating Atomic Mass for Calculating Atomic Mass for ChlorineChlorine

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Isotopes of Some Elements Isotopes of Some Elements and Their Atomic Massand Their Atomic Mass

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2.6 Electron Energy 2.6 Electron Energy LevelsLevels

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Electromagnetic RadiationElectromagnetic Radiation

Electromagnetic radiationElectromagnetic radiation Consists of energy particles called Consists of energy particles called

photons that travel as waves.photons that travel as waves. Includes low energy particles that Includes low energy particles that

have long wavelengths and high have long wavelengths and high energy particles that have short energy particles that have short wavelengths.wavelengths.

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Electromagnetic SpectrumElectromagnetic Spectrum

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Electrons are Electrons are arranged in specific arranged in specific energy levels called energy levels called shells. shells.

The first energy The first energy level (n=1) contains level (n=1) contains electrons that have electrons that have the lowest energy.the lowest energy.

The energy levels The energy levels are labeled 1, 2, 3, are labeled 1, 2, 3, and so on.and so on.

Electron Energy LevelsElectron Energy Levels

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Electrons of similar energy are Electrons of similar energy are grouped in energy levels. grouped in energy levels.

The maximum number of electrons The maximum number of electrons in any energy level is equal to 2nin any energy level is equal to 2n22..

n = 1n = 1 2(1)2(1)22 = = 2 2n = 2n = 2 2(2)2(2)22 = = 8 8n = 3n = 3 2(3)2(3)22 == 1818n = 4n = 4 2(4)2(4)22 == 3232

Number of ElectronsNumber of Electrons

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The order in which electrons enter The order in which electrons enter and fill the shells for the first 20 and fill the shells for the first 20 electrons iselectrons is

Shell numberShell number11 22 33 442e2e 8e8e 8e8e 2e2e

Although shell 3 can eventually Although shell 3 can eventually hold 18 electrons, it fills to 8 first.hold 18 electrons, it fills to 8 first.

Order of Electron FillingOrder of Electron Filling

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In the In the electron shell electron shell arrangementarrangement, the electrons in , the electrons in each shell of an atom are listed each shell of an atom are listed in order of increasing energy.in order of increasing energy. Element Element Shell Shell

1 1 22 33HeHe 22FF 2 2 77NeNe 2 2 88AlAl 2 2 88 33ClCl 22 8 8 77

Electron Shell ArrangementElectron Shell Arrangement

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All the elements in a group have the All the elements in a group have the same number of electrons in their same number of electrons in their outermost shells.outermost shells.

Elements in a group have similar Elements in a group have similar chemical and physical properties.chemical and physical properties.Example: Example: Group 2Group 2

BeBe 2, 22, 2

Mg 2, 8, 2Mg 2, 8, 2

Ca Ca 2, 8, 8, 22, 8, 8, 2

Periodic LawPeriodic Law

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Energy Level ChangesEnergy Level Changes

Electrons are in discrete Electrons are in discrete energy levels. energy levels.

An electron absorbs An electron absorbs energy to “jump” to a energy to “jump” to a higher energy level. higher energy level.

When an electron falls to When an electron falls to a lower energy level, a lower energy level, energy is emitted. energy is emitted.

In the visible range, the In the visible range, the emitted energy appears as emitted energy appears as a color.a color.

2.6 Electron Energy Levels2.6 Electron Energy Levels

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2.7 Subshells and 2.7 Subshells and OrbitalsOrbitals

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Within each energy level, Within each energy level, electrons are grouped into electrons are grouped into energy sublevels or subshells.energy sublevels or subshells.

All electrons in a subshell All electrons in a subshell have the same energy.have the same energy.

The different The different subshellssubshells are are designateddesignated by the letters by the letters s, p, s, p, d, fd, f..

SubshellsSubshells

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Number of Subshells in a Number of Subshells in a ShellShell

The number of subshells in each shell The number of subshells in each shell is the same as the shell number.is the same as the shell number.

Shell Shell Number of Number of Types of Types of NumberNumber Subshells Subshells SubshellsSubshellsn=4n=4 44 4s, 4p, 4d, 4f4s, 4p, 4d, 4fn=3n=3 33 3s, 3p, 3d3s, 3p, 3dn=2n=2 22 2s, 2p2s, 2pn=1n=1 11 1s1s

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Energy Levels of SubshellsEnergy Levels of Subshells

The The s s subshell has the lowest subshell has the lowest energy in any shell followed by the energy in any shell followed by the p, d, p, d, andand f f subshells. subshells.

33ddn = 3n = 3 33pp

33ss

22pp22ss

n = 1n = 1 11ss

n = 2

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An An orbitalorbital is a 3 dimensional space is a 3 dimensional space around a nucleus in which an around a nucleus in which an electron is most likely to be found. electron is most likely to be found.

The shape represents electron The shape represents electron density (density (not a path the electron not a path the electron follows).follows).

Each orbitalEach orbital can hold up to can hold up to 2 2 electronselectrons..

OrbitalsOrbitals

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Subshells and OrbitalsSubshells and Orbitals

Each subshell has a specific number of Each subshell has a specific number of orbitalsorbitals. .

Each Each ss subshell subshell contains one contains one ss orbital. orbital. Each Each pp subshell subshell contains contains three three pp orbitals orbitals.. Each Each dd subshell subshell contains contains five five dd orbitals orbitals.. Each Each ff subshell subshell contains contains seven seven ff orbitals orbitals..

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ss and and pp Orbitals Orbitals

In an atom, In an atom, all the orbitals are all the orbitals are centered around the nucleuscentered around the nucleus. For . For example, the illustration of the example, the illustration of the combination of combination of ss and and pp orbitals is orbitals is

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Electrons in Each SubshellElectrons in Each Subshell

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2.8 Electron 2.8 Electron ConfigurationsConfigurations

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An An electron configuration:electron configuration: Is a list of the subshells and the number Is a list of the subshells and the number

of electrons in each in order of increasing of electrons in each in order of increasing energy.energy.

Contains superscripts that give the Contains superscripts that give the number of electrons in each subshell. number of electrons in each subshell.

Of neon is as follows: Of neon is as follows: number of electrons in each subshellnumber of electrons in each subshell

1s1s22 2s2s22 2p2p66

Electron ConfigurationElectron Configuration

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Subshell Location on the Subshell Location on the Periodic TablePeriodic Table

The periodic table contains subshell blocks The periodic table contains subshell blocks arranged in order of increasing energy.arranged in order of increasing energy.

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There is a specific number of There is a specific number of electrons in each subshell block.electrons in each subshell block.

1 1 ss11 s s22 p p11 p p2 2

pp3 3 pp44 p p55 p p66

2233 dd11 - d - d1010

445566

f1 - f14

Subshell BlocksSubshell Blocks

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An electron configuration is written by:An electron configuration is written by: Locating the element on the periodic table.Locating the element on the periodic table. Starting with H and writing each subshell Starting with H and writing each subshell

notation and electrons in order.notation and electrons in order.

Groups 1-2 Groups 1-2 = = ss level level

Groups 3-8Groups 3-8 = = pp level level

TransitionTransition = = dd level level

Lanthanides/Actinides Lanthanides/Actinides = = ff level level

Writing an Electron Writing an Electron ConfigurationConfiguration

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First PeriodFirst PeriodHH 1s1s11

He He 1s1s22

Second PeriodSecond PeriodLiLi 1s1s22 2s2s11

CC 1s1s22 2s2s22 2p2p22

Third PeriodThird PeriodNaNa 1s1s22 2s2s22 2p2p66 3s3s11

AlAl 1s1s22 2s2s22 2p2p66 3s3s22 3p3p11

SS 1s1s22 2s2s22 2p2p66 3s3s22 3p3p44

Some Electron Some Electron ConfigurationsConfigurations

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Electron Configurations for Electron Configurations for Atomic Numbers 1-18Atomic Numbers 1-18

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Electron Configurations for Electron Configurations for Elements 19-36Elements 19-36

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Noble Gas NotationNoble Gas Notation

A noble gas notation is used to A noble gas notation is used to abbreviate the completed subshells abbreviate the completed subshells as [noble gas].as [noble gas].

For example, the complete For example, the complete configuration of bromine isconfiguration of bromine is

1s1s22 2s 2s2 2 2p2p66 3s 3s22 3p 3p66 4s4s22 3d 3d10 10 4p4p55

Ar configurationAr configuration The noble gas notation for bromine isThe noble gas notation for bromine is [Ar] [Ar] 4s4s22 3d 3d10 10 4p4p55

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Group Numbers and Group Numbers and SubshellsSubshells

The Group Number is the sum of the The Group Number is the sum of the ss and and pp electrons in the outermost shell. electrons in the outermost shell.