Chapter 10 Molecular Structure: Solids and Liquids.

Chapter 10Chapter 10Molecular Structure: Molecular Structure:

Solids and LiquidsSolids and Liquids

HomeworkHomework Assigned Problems (Assigned Problems (oddodd numbers only) numbers only)

““Questions and Problems” 10.1 to 10.53 Questions and Problems” 10.1 to 10.53 (begins on page 292)(begins on page 292)

““Additional Questions and Problems” 10.65 to Additional Questions and Problems” 10.65 to 10.91 (page 325)10.91 (page 325)

““Challenge Questions” 10.93 to 10.99, Challenge Questions” 10.93 to 10.99, (page 327)(page 327)

Representing Valence Electrons with Dots: Representing Valence Electrons with Dots: Electron-Dot FormulasElectron-Dot Formulas

The valence electrons are the most The valence electrons are the most important (chemically) electrons in the atomimportant (chemically) electrons in the atom

These electrons are situated in the highest, These electrons are situated in the highest, occupied principal energy level (n)occupied principal energy level (n)

They are farthest from the nucleus , away They are farthest from the nucleus , away from the stable (filled) inner core of electronsfrom the stable (filled) inner core of electrons

Determine the chemical properties of an Determine the chemical properties of an elementelement


In the main-group elements, the valence In the main-group elements, the valence electrons are the in the outermost s- and electrons are the in the outermost s- and p- orbitalsp- orbitals

The Roman numeral at the top of each The Roman numeral at the top of each column represents the number of valence column represents the number of valence electrons in each member of that groupelectrons in each member of that group

The valence electrons for the main-group The valence electrons for the main-group elements can be represented by elements can be represented by Lewis Lewis StructuresStructures


The Lewis (Dot) structure consists of an The Lewis (Dot) structure consists of an elements symbol with one dot per each elements symbol with one dot per each valence electron placed about the valence electron placed about the element’s symbolelement’s symbol

The representative elements in the same The representative elements in the same group have the same number of valence group have the same number of valence electronselectrons

The maximum number of valence The maximum number of valence electrons for any element is eightelectrons for any element is eight


Only the noble Only the noble gases have the gases have the maximum maximum number of eight number of eight electronselectrons

The exception is The exception is helium with only helium with only two valence two valence electronselectrons

Octet rule

Duet rule


Example: dot structures for Example: dot structures for representative elements in period 2representative elements in period 2

The valence electrons are in the The valence electrons are in the outer s and p orbitalsouter s and p orbitals

Li• Be• •B• •C• •N• •O: :F: :Ne:• •

•

• • • •

•• •• •• ••

••

outer electron configuration

ns1 ns2np1ns2 ns2np2 ns2np3 ns2np4 ns2np5 ns2np6


The force of attraction between two The force of attraction between two types of atoms is a types of atoms is a chemical bondchemical bond

The ionic bond The ionic bond is the attraction is the attraction between positive and negative ionsbetween positive and negative ions

Compounds held together by ionic Compounds held together by ionic bonds are called ionic compoundsbonds are called ionic compounds

Each element forms an ion with a Each element forms an ion with a stable noble gas configurationstable noble gas configuration

Lewis Structures for Ionic Compounds: Lewis Structures for Ionic Compounds: Electrons TransferredElectrons Transferred

During ionic bond formation, ions form During ionic bond formation, ions form when atoms of two elements are present: when atoms of two elements are present: An element that can lose electrons and an An element that can lose electrons and an element that can gain electronselement that can gain electrons

The most stable of all outer electron The most stable of all outer electron configurations is based on the chemical configurations is based on the chemical properties of the noble gasesproperties of the noble gases

By chemical reactions and compound By chemical reactions and compound formation, elements can attain a stable formation, elements can attain a stable outer electron configuration outer electron configuration


Metals: Low ionization energy, form Metals: Low ionization energy, form ions (ions (cationscations))

Nonmetals: High ionization energy, Nonmetals: High ionization energy, accept electrons (accept electrons (anionsanions))

The representative elements lose or The representative elements lose or gain electrons to form ions with outer gain electrons to form ions with outer electron configuration of the nearest electron configuration of the nearest noble gasnoble gas

Electron Configuration of IonsElectron Configuration of Ions

An ion: An atom that is electrically An ion: An atom that is electrically charged from loss or gain of charged from loss or gain of electronselectrons

Atoms are neutral due to the equal Atoms are neutral due to the equal number of protons and electrons number of protons and electrons

Loss or gain of an electron will leave Loss or gain of an electron will leave a net charge on the atom a net charge on the atom

Electron Configuration of IonsElectron Configuration of Ions Consider sodiumConsider sodium

Can attain the noble gas configuration (neon) Can attain the noble gas configuration (neon) if it loses 1 electron to obtain Naif it loses 1 electron to obtain Na++

Noble gas core remains but it Noble gas core remains but it does notdoes not have have the same chemical properties of neonthe same chemical properties of neon

1s22s22p63s1

NaLoss of 1 e-

1s22s22p6

Electron configuration of neon

Na+

Electron Configuration of IonsElectron Configuration of Ions Consider chlorineConsider chlorine

Can attain the noble gas configuration Can attain the noble gas configuration (argon) if it gains 1 electron to obtain Cl(argon) if it gains 1 electron to obtain Cl--

Attains same E configuration of the nearest Attains same E configuration of the nearest noble gas but it noble gas but it does notdoes not have the same have the same chemical properties of argonchemical properties of argon

1s22s22p63s23p5

ClGain of 1 e-

1s22s22p63s23p6

Electron configuration of argon

Cl-

Electron ConfigurationsElectron Configurations We know for Representative Elements: We know for Representative Elements:

• Group 1A metals form ions with Group 1A metals form ions with +1+1 charge charge• Group 2A metals form ions with Group 2A metals form ions with +2+2 charge charge• Group 7A nonmetals form ions with Group 7A nonmetals form ions with -1-1 charge charge• Group 6A nonmetals form ions with Group 6A nonmetals form ions with -2-2 charge charge• Group 8A nonmetals do not form ions, in fact they Group 8A nonmetals do not form ions, in fact they

are extremely unreactiveare extremely unreactive

Transition Elements: All of the elements of the d area Transition Elements: All of the elements of the d area of the periodic tableof the periodic table• Elements differ in the number of electrons in the d Elements differ in the number of electrons in the d

subshellsubshell• Octet rule does not apply hereOctet rule does not apply here• Loss of electrons does not lead to the noble gas Loss of electrons does not lead to the noble gas

structurestructure

Ions of the Metals of Groups IA, Ions of the Metals of Groups IA, IIA, IIIAIIA, IIIA

Metals form Metals form cations by cations by losinglosing enough electrons enough electrons to get the same to get the same electron electron configuration as configuration as the the previousprevious noble noble gasgas

A stable A stable noble gas noble gas corecore attained in attained in each caseeach case

Atom

Atoms Electron Config

Ion Ions Electron Config

Na [Ne]3s1 Na+1 [Ne]

Mg [Ne]3s2 Mg+2 [Ne]

Al [Ne]3s23p1 Al+3 [Ne]

O [He]2s22p4 O-2 [Ne]

F [He]2s22p5 F-1 [Ne]

Ions of the Nonmetals of Group Ions of the Nonmetals of Group VIA, VIIAVIA, VIIA

Nonmetals form Nonmetals form anions by anions by gaininggaining enough electrons enough electrons to get the same to get the same electron electron configuration as configuration as the the nextnext noble gas noble gas

A stable A stable noble gas noble gas corecore attained in attained in each caseeach case

Atom Atoms Electron Config

Ion Ions Electron Config

Na [Ne]3s1 Na+1 [Ne]

Mg [Ne]3s2 Mg+2 [Ne]

Al [Ne]3s23p1 Al+3 [Ne]

O [He]2s22p4 O-2 [Ne]

F [He]2s22p5 F-1 [Ne]


Sodium ChlorideSodium Chloride• Formed from Formed from

sodium and sodium and chlorine atomschlorine atoms

• An ionic bond An ionic bond forms consisting forms consisting of a sodium ion of a sodium ion (+ charge) and (+ charge) and a chloride ion a chloride ion (- charge) (- charge)

• Each sodium loses Each sodium loses one electron to one electron to achieve an octet achieve an octet

• Each chlorine atom Each chlorine atom gains one electron gains one electron to achieve an octetto achieve an octet

• Formula is Formula is NaClNaCl

••

•• •• ••


Magnesium Magnesium ChlorideChloride• Formed from Formed from

magnesium and magnesium and two chlorinestwo chlorines

• An ionic bond An ionic bond forms consisting forms consisting of a magnesium of a magnesium ion (2+ charge) ion (2+ charge) and and two chloride ions two chloride ions (- charge (- charge each)each)

• Each magnesium Each magnesium loses two electrons loses two electrons to achieve an octet to achieve an octet

• Each chlorine atom Each chlorine atom gains one electron gains one electron to achieve an octetto achieve an octet

• Formula is Formula is MgClMgCl22


Bonding involves ONLY valence electronsBonding involves ONLY valence electrons Transfer of the s and p valence electrons Transfer of the s and p valence electrons

achieves stability of the nearest noble gasachieves stability of the nearest noble gas Illustrates the sequence of atomsIllustrates the sequence of atoms Shows atoms and their valence electronsShows atoms and their valence electrons

• How they are distributed in a moleculeHow they are distributed in a molecule• Use a dot or X to represent an electronUse a dot or X to represent an electron

Li• Be• •B• •C• •N• •O: :F: :Ne:• •

•

• • • •

•• •• •• ••

••

Li• Li1+ :F: [:F:]1-

•

•• ••

••

Give the number of valence electrons for Give the number of valence electrons for Mg, N, and Br. Draw the Lewis dot symbol Mg, N, and Br. Draw the Lewis dot symbol for each of these elementsfor each of these elements


Mg: 2 valence electrons

N: 5 valence electrons

Br: 7 valence electrons

Mg

Br

N

Covalent Lewis Structures:Covalent Lewis Structures:Electrons SharedElectrons Shared

Chemical bonding also occurs between Chemical bonding also occurs between two nonmetalstwo nonmetals

Since nonmetals do not readily lose Since nonmetals do not readily lose electrons, when two nonmetals bind electrons, when two nonmetals bind together the electrons are sharedtogether the electrons are shared

A A covalent bond covalent bond is a pair of electrons is a pair of electrons shared by two atomsshared by two atoms

It is the binding force that results from two It is the binding force that results from two nuclei attracting the same shared nuclei attracting the same shared electronselectrons


A covalent Lewis structure: A 2-D A covalent Lewis structure: A 2-D representation of how atoms are representation of how atoms are covalently bonded togethercovalently bonded together

Each covalent bond is represented by a Each covalent bond is represented by a pair of dots (pair of dots (bonding electronsbonding electrons))

Must also show all unshared pairs of Must also show all unshared pairs of ((nonbondingnonbonding) electrons) electrons

All valence eAll valence e-- from every atom in a from every atom in a molecule must be accounted for in the molecule must be accounted for in the form of bonds or nonbonding pairsform of bonds or nonbonding pairs


The atoms in covalently The atoms in covalently bonded molecules often have bonded molecules often have bonding and nonbonding bonding and nonbonding electronselectrons

The number of covalent The number of covalent bonds that an atom forms is bonds that an atom forms is equal to the number of equal to the number of electrons needed to form a electrons needed to form a noble gas configuration noble gas configuration (octet)(octet)

The exception is hydrogen The exception is hydrogen which needs only two which needs only two electronselectrons

Shared electrons can be also Shared electrons can be also represented by dashesrepresented by dashes

Formation of a Hydrogen MoleculeFormation of a Hydrogen Molecule

The simplest covalent The simplest covalent bonding conditionbonding condition

Hydrogen has one 1s Hydrogen has one 1s electronelectron

H atom requires one H atom requires one additional electron to additional electron to obtain the stable obtain the stable noble gas noble gas configurationconfiguration of of heliumhelium

Each H atom Each H atom contributes its one contributes its one electronelectron

The electron pair The electron pair shared by the two shared by the two atoms, forming atoms, forming diatomic hydrogen diatomic hydrogen HH22

Covalent Lewis Structure: Electrons SharedCovalent Lewis Structure: Electrons Shared

Duet RuleDuet Rule• Hydrogen wants two electrons to attain the Hydrogen wants two electrons to attain the

noble gas configuration of heliumnoble gas configuration of helium Octet RuleOctet Rule

• All other main group elements want 8 All other main group elements want 8 electrons to achieve electrons to achieve the noble gas the noble gas configurationconfiguration

• Filled valence shell is achieved by Filled valence shell is achieved by gaining/losing electrons or by gaining/losing electrons or by sharingsharing electronselectrons

Covalent Lewis Structures:Covalent Lewis Structures:Double and Triple Bonds Double and Triple Bonds

A single covalent bond is where two atoms A single covalent bond is where two atoms share one pair of valence electronsshare one pair of valence electrons

Many molecules exist that need two or Many molecules exist that need two or three pairs of electrons to provide a three pairs of electrons to provide a complete octet of electrons per atomcomplete octet of electrons per atom

Multiple covalent bonds: Multiple covalent bonds: Covalent bonds Covalent bonds where two pairs or three pairs of valence where two pairs or three pairs of valence electrons are shared between the same electrons are shared between the same two atomstwo atoms


Two identical nonmetal atoms (diatomic Two identical nonmetal atoms (diatomic molecules)molecules)

Each atom will share valence electrons with Each atom will share valence electrons with the other the other

The shared pair of electrons allow each atom The shared pair of electrons allow each atom to achieve a stable to achieve a stable noble gas configurationnoble gas configuration

This configuration can be achieved by aThis configuration can be achieved by a single, double, or triple single, double, or triple shared pair of shared pair of electronselectrons

●●

●●

●● ●●●

●●●


Single Bond is a chemical bond where two Single Bond is a chemical bond where two atoms share atoms share one pairone pair of valence electrons of valence electrons

Double Bond is a chemical bond where two Double Bond is a chemical bond where two atoms share atoms share two pairstwo pairs of valence electrons of valence electrons

Triple Bond is a chemical bond where two Triple Bond is a chemical bond where two atoms share atoms share three pairsthree pairs of valence electrons of valence electrons

NNOOF F

Sharing Electrons Between Atoms Sharing Electrons Between Atoms of Different Elementsof Different Elements

Two nonidentical Two nonidentical nonmetal atomsnonmetal atoms

The number of The number of covalent bonds an covalent bonds an atom forms will equal atom forms will equal the number of the number of electrons needed to electrons needed to form a stable, form a stable, noble noble gas configurationgas configuration

Hydrogen follows the Hydrogen follows the duet rule and forms a duet rule and forms a stable,stable, helium noble helium noble gas configurationgas configuration

Bonding Behavior of Elements Bonding Behavior of Elements Oxygen has 6 valence Oxygen has 6 valence

electrons and 2 octet electrons and 2 octet vacanciesvacancies

Can complete its octet Can complete its octet by forming two by forming two covalent bondscovalent bonds

Nitrogen has 5 Nitrogen has 5 valence electrons and valence electrons and 3 octet vacancies3 octet vacancies

Can complete its octet Can complete its octet by forming three by forming three covalent bondscovalent bonds

OGroup 6A

N

Group 5A

Bonding Behavior of ElementsBonding Behavior of Elements Carbon has 4 valence Carbon has 4 valence

electrons and 4 octet electrons and 4 octet vacanciesvacancies

Can complete its octet Can complete its octet by forming four by forming four covalent bondscovalent bonds

Fluorine has 7 valence Fluorine has 7 valence electrons and 1 octet electrons and 1 octet vacancyvacancy

Can complete its octet Can complete its octet by forming one by forming one covalent bondcovalent bond

C

FGroup 7A

Group 4A

Bonding Behavior of ElementsBonding Behavior of Elements

C N

O F

Group 4A Group 5A

Group 6A Group 7A

Writing Lewis Structures for Writing Lewis Structures for Covalent CompoundsCovalent Compounds

A dot structure is a two-dimensional A dot structure is a two-dimensional representation of a molecule to show how representation of a molecule to show how atoms are joined together by covalent atoms are joined together by covalent bondingbonding

To write a dot structure:To write a dot structure: A bond is shown as a pair of dots or a dashA bond is shown as a pair of dots or a dash Dot structures also show the location of Dot structures also show the location of

electron pairs not used in bondselectron pairs not used in bonds All valence electrons from every atom in the All valence electrons from every atom in the

molecule or PA ion must be accounted formolecule or PA ion must be accounted for


1)1) Determine the arrangement of Determine the arrangement of atoms within a moleculeatoms within a molecule• If there are three or more atoms, If there are three or more atoms,

the central atomthe central atom (usually) appears (usually) appears only once in the formula only once in the formula

• Halogens are often terminal atoms Halogens are often terminal atoms (at the ends) unless it is combined (at the ends) unless it is combined with O as in oxyacidswith O as in oxyacids

• Hydrogen is Hydrogen is alwaysalways a terminal a terminal atomatom


2)2) Determine the total number of Determine the total number of valence electronsvalence electrons• For main-group elements the group For main-group elements the group

numbers equal the number of numbers equal the number of valence electrons for the element of valence electrons for the element of that groupthat group

• If it is an anion, add one electron to If it is an anion, add one electron to the total for each negative chargethe total for each negative charge

• If it is a cation, subtract one electron If it is a cation, subtract one electron from the total for each positive from the total for each positive chargecharge


3)3) Attach the central atom to each Attach the central atom to each bonded atom by a pair of electronsbonded atom by a pair of electrons• Subtract two electrons (from total Subtract two electrons (from total

valence) for each single bond drawn valence) for each single bond drawn in the structurein the structure


4)4) Distribute the remaining electronsDistribute the remaining electrons

• Add electrons to each atom Add electrons to each atom bonded to the central atom until bonded to the central atom until each has eight electrons (octet each has eight electrons (octet rule) rule)

• Exception: hydrogen (duet rule)Exception: hydrogen (duet rule)

• Any extra electrons should go to Any extra electrons should go to the central atomsthe central atoms


5)5) If the central atom does not fulfill If the central atom does not fulfill the octet rule, share one or more the octet rule, share one or more lone pairs between a terminal atom lone pairs between a terminal atom and the central atom (form multiple and the central atom (form multiple covalent bonds)covalent bonds)• Double or triple bonds are formed Double or triple bonds are formed

ONLY when one or both of the atoms ONLY when one or both of the atoms are are C, N, O or SC, N, O or S


Example: Create the electron-dot formula for Example: Create the electron-dot formula for Fluorine gas = FFluorine gas = F22

•Determine the arrangement of the atomsDetermine the arrangement of the atoms

• Determine the total number of valence electrons Determine the total number of valence electrons for the dot structure (2 × 7 = 14)for the dot structure (2 × 7 = 14)

• Begin with bonding electronsBegin with bonding electrons• Distribute the remaining electrons among the Distribute the remaining electrons among the

two atoms, giving octets to each fluorine atom, two atoms, giving octets to each fluorine atom, then proceed to lone pairs on each atomthen proceed to lone pairs on each atom

F FF F ● ●

Writing Lewis Structures forWriting Lewis Structures forCovalent Compounds and Polyatomic IonsCovalent Compounds and Polyatomic Ions

Write a Lewis structure for the Write a Lewis structure for the following:following:

• NHNH44++

• SOSO442-2-

• COCO• SCNSCN--

C O

Writing Lewis Structures forWriting Lewis Structures forCovalent Compounds: COCovalent Compounds: CO

Determine the arrangement of the atomsDetermine the arrangement of the atoms C: 4 electronsC: 4 electrons O: 6 electronsO: 6 electrons Total valence electrons: 10Total valence electrons: 10 If octets are not complete, form one or If octets are not complete, form one or

more multiple covalent bondsmore multiple covalent bonds

C O

Writing Lewis Structures forWriting Lewis Structures forPolyatomic Ions: NHPolyatomic Ions: NH44

++

Determine the Determine the arrangement of the atomsarrangement of the atoms

Total number of valence eTotal number of valence e--

N: 5 valence electronsN: 5 valence electrons H: 4×1 valence electronH: 4×1 valence electron Positive Charge: Subtract Positive Charge: Subtract

one electronone electron Total valence electrons: 8Total valence electrons: 8

N H

H

H

H

+

Writing Lewis Structures forWriting Lewis Structures forPolyatomic Ions: SOPolyatomic Ions: SO44

2-2-

Determine the arrangement of the atomsDetermine the arrangement of the atoms Total number of valence electronsTotal number of valence electrons S: 6 valence electronsS: 6 valence electrons O: 4 x 6 valence electronsO: 4 x 6 valence electrons Negative Charge: Add two electronsNegative Charge: Add two electrons Total valence electrons: 32Total valence electrons: 32

2-

S O

O

O

O

C NS

Writing Lewis Structures forWriting Lewis Structures forPolyatomic Ions: SCNPolyatomic Ions: SCN--

Determine the arrangement of the atomsDetermine the arrangement of the atoms Total number of valence electrons:Total number of valence electrons:

• S: 6 electronsS: 6 electrons• C: 4 electronsC: 4 electrons• N: 5 electronsN: 5 electrons

Charge: add one electron Charge: add one electron Total electrons: 16Total electrons: 16 If octets are not complete, form one or more If octets are not complete, form one or more

multiple covalent bondsmultiple covalent bonds

C NS-

Resonance: Equivalent Lewis StructuresResonance: Equivalent Lewis Structuresfor the Same Moleculefor the Same Molecule

ResonanceResonance occurs when no single dot occurs when no single dot structure adequately describes bonding structure adequately describes bonding in moleculein molecule

Resonance structures are two or more Resonance structures are two or more dot structures for a molecule or ion that dot structures for a molecule or ion that has the same arrangement of atomshas the same arrangement of atoms

Contain the same number of electronsContain the same number of electrons Differ only in the location of electronsDiffer only in the location of electrons The true structure is the average of the The true structure is the average of the

individual structuresindividual structures

Writing Resonance StructuresWriting Resonance Structures

Write a Lewis structure for nitrate ion and Write a Lewis structure for nitrate ion and include resonance structuresinclude resonance structures

Determine the arrangement of the atomsDetermine the arrangement of the atoms Total number of valence electrons Total number of valence electrons

Use a double-headed arrow to connect the Use a double-headed arrow to connect the structures structures

NO

OO

-

NO

OO

-

NO

OO

-

(3 ×6) + 5 + 1 = 24 valence elec


Write a Lewis structure for ozone and Write a Lewis structure for ozone and include resonance structures (Oinclude resonance structures (O33))

Determine the arrangement of the atomsDetermine the arrangement of the atoms Total number of valence electronsTotal number of valence electrons

The actual structure is called a “resonance The actual structure is called a “resonance hybrid” of the two contributing structureshybrid” of the two contributing structures

Resonance structures Hybrid

3 ×6 = 18 valence elec


C

C

C C

C

C C

C

C C

C

CH H

HH

H H

H H

H H

H H

Predicting the Shapes of MoleculesPredicting the Shapes of Molecules

(Lewis) Dot structures describe the (Lewis) Dot structures describe the distribution of valence electrons distribution of valence electrons among bonding pairs and among bonding pairs and nonbonding pairs nonbonding pairs

They do not give info on the 3-D They do not give info on the 3-D shape of the moleculeshape of the molecule

The 3-D arrangement of atoms in a The 3-D arrangement of atoms in a molecule is determined by its molecule is determined by its molecular geometrymolecular geometry

Predicting the Shapes of MoleculesPredicting the Shapes of Molecules A Lewis structure for waterA Lewis structure for water

Are the atoms arranged in a straight line Are the atoms arranged in a straight line or do they form a v-shape?or do they form a v-shape?

••

••

••

••

HO

H

H O H

Predicting the Shapes of MoleculesPredicting the Shapes of MoleculesVSEPR TheoryVSEPR Theory

The 3-D shapes of molecules and PA The 3-D shapes of molecules and PA ions result from the orientation of ions result from the orientation of atoms about the central atomatoms about the central atom

VSEPR: VSEPR: Valence Shell Electron-Pair Valence Shell Electron-Pair Repulsion TheoryRepulsion Theory focuses on the focuses on the bonding and nonbonding electrons in bonding and nonbonding electrons in the valence shell of the central atom the valence shell of the central atom

Predicting the Shapes of MoleculesPredicting the Shapes of MoleculesVSEPR TheoryVSEPR Theory

The central atom’s electrons play The central atom’s electrons play an important role in determining an important role in determining molecular shapemolecular shape

Bonding and nonbonding pairs of Bonding and nonbonding pairs of electrons have a natural electrostatic electrons have a natural electrostatic repulsion that pushes them as far repulsion that pushes them as far apart from one another as apart from one another as possiblepossible

Predicting the Shapes of Molecules Predicting the Shapes of Molecules

VSEPR TheoryVSEPR Theory It is this repulsion of electron groups It is this repulsion of electron groups (regions of negative charge) that (regions of negative charge) that causes a molecule to have a certain causes a molecule to have a certain shape: shape: molecular geometrymolecular geometry

The central concept of VSEPR theory The central concept of VSEPR theory is that the electron pairs in the is that the electron pairs in the valence shell of atoms form an valence shell of atoms form an arrangement in space that minimizes arrangement in space that minimizes the repulsion between the electron the repulsion between the electron pairs: pairs: electron geometryelectron geometry

Electron GeometriesElectron Geometries

Two electron groupsTwo electron groups• 2 atoms attached2 atoms attached• Shape: Shape: LinearLinear• Bond angle: 180°Bond angle: 180°

Three electron groups Three electron groups • 3 atoms attached3 atoms attached• Shape: Shape: Trigonal PlanarTrigonal Planar• Bond angle: 120°Bond angle: 120°

Four electron groupsFour electron groups• 4 atoms attached4 atoms attached• Shape: Shape: TetrahedralTetrahedral• Bond angle 109.5°Bond angle 109.5°

Molecular GeometriesMolecular GeometriesLinearLinear

• 2 electron groups2 electron groups• 2 bonding groups2 bonding groups, 0 lone pairs, 0 lone pairs• 2 atoms on opposite sides of 2 atoms on opposite sides of

the central atomthe central atom• 180° bond angles180° bond angles

Trigonal PlanarTrigonal Planar• 3 electron groups3 electron groups• 3 bonding groups3 bonding groups, 0 one pairs, 0 one pairs• 3 atoms form a triangle around 3 atoms form a triangle around

the central atomthe central atom• 120° bond angles120° bond angles

180°

120°

Molecular GeometriesMolecular Geometries

TetrahedralTetrahedral• 4 electron groups4 electron groups• 4 bonding groups4 bonding groups, 0 lone pairs, 0 lone pairs• 4 surrounding atoms form a 4 surrounding atoms form a

tetrahedron around the tetrahedron around the central atomcentral atom

• 109.5° bond angles109.5° bond angles

109.5°

Predicting the Shapes of moleculesPredicting the Shapes of moleculesVSEPR TheoryVSEPR Theory

Example: beryllium fluorideExample: beryllium fluoride• 2 electron groups and 2 bonding groups2 electron groups and 2 bonding groups• 0 lone pairs 0 lone pairs • Beryllium does not follow the octet ruleBeryllium does not follow the octet rule• Electron geometry: Electron geometry: linear linear • Angle between electron groups: 180°Angle between electron groups: 180°• Molecular geometry: Molecular geometry: linearlinear

F Be F180°

Shapes of molecules and ionsShapes of molecules and ionsVSEPR TheoryVSEPR Theory

Example: boron trifluorideExample: boron trifluoride• 3 electron groups, 3 bonding groups, 0 lone 3 electron groups, 3 bonding groups, 0 lone

pairspairs• Boron does not follow the octet ruleBoron does not follow the octet rule• Electron geometry: Electron geometry: trigonal planartrigonal planar• Angle between electron groups: 120° Angle between electron groups: 120° • Molecular geometry: Molecular geometry: trigonal planartrigonal planar

F BF

F

120°

Shapes of molecules and ionsShapes of molecules and ionsVSEPR TheoryVSEPR Theory

Example: carbon tetrafluorideExample: carbon tetrafluoride 4 electron groups, 4 bonding groups, 0 lone pairs4 electron groups, 4 bonding groups, 0 lone pairs Electron geometry:Electron geometry: tetrahedral tetrahedral Angle between electron groups: 109.5°Angle between electron groups: 109.5° Molecular geometry: Molecular geometry: tetrahedraltetrahedral

F

FC

FF 109.5°

VSEPR Theory: Central Atoms with VSEPR Theory: Central Atoms with Bonding Pairs and Lone PairsBonding Pairs and Lone Pairs

Often the 3-D shape (molec. geometry) is Often the 3-D shape (molec. geometry) is not described the same as the electron not described the same as the electron geometry geometry

The The electron-pair geometryelectron-pair geometry around a around a central atom includes the spatial central atom includes the spatial positions of all bond pairs and lone pairspositions of all bond pairs and lone pairs

Only the arrangement of atoms describes Only the arrangement of atoms describes the the molecular geometry molecular geometry of the molecule, of the molecule, not the lone pairs of electronsnot the lone pairs of electrons becausebecause you can’t actually see lone pairs, you can you can’t actually see lone pairs, you can only see the atomsonly see the atoms

VSEPR Theory: Central Atoms with Bonding VSEPR Theory: Central Atoms with Bonding Pairs and Lone PairsPairs and Lone Pairs

Example: ammonia gasExample: ammonia gas 4 electron groups, 3 bonding groups, 1 4 electron groups, 3 bonding groups, 1

lone pair lone pair 3 atoms attached to the central atom 3 atoms attached to the central atom A A tetrahedraltetrahedral electron geometry electron geometry Angle between electron groups: 109.5°Angle between electron groups: 109.5° A A trigonal pyramidaltrigonal pyramidal molecular geometry molecular geometry

HN

HH

VSEPR Theory: Central atoms with Bonding VSEPR Theory: Central atoms with Bonding Pairs and Lone PairsPairs and Lone Pairs

Example: WaterExample: Water 4 electron groups, 2 bonding groups, 2 4 electron groups, 2 bonding groups, 2

lone pairslone pairs 2 atoms attached to the central atom2 atoms attached to the central atom A A tetrahedraltetrahedral electron geometry electron geometry Angle between electron groups: 109.5°Angle between electron groups: 109.5° AA bent bent molecular geometry molecular geometry

HO

H

Electronegativity and PolarityElectronegativity and Polarity

ElectronegativityElectronegativity is the ability of an atom is the ability of an atom in a molecule to attract bonding in a molecule to attract bonding electrons towards itselfelectrons towards itself

The higher the element’s The higher the element’s electronegativity, the greater its ability to electronegativity, the greater its ability to attract electrons attract electrons

Electronegativity and PolarityElectronegativity and Polarity ElectronegativityElectronegativity

• IncreasesIncreases across a period (left to right) on the across a period (left to right) on the periodic tableperiodic table

• DecreasesDecreases down group (top to bottom) on the down group (top to bottom) on the periodic tableperiodic table

In general:In general:• Nonmetals have higher electronegativity Nonmetals have higher electronegativity

values than metals and nonmetals tend to values than metals and nonmetals tend to gain electronsgain electrons

• Metals have lower electronegativity values Metals have lower electronegativity values and tend to lose electronsand tend to lose electrons

• This occurs when an ionic bond is formedThis occurs when an ionic bond is formed

ElectronegativityElectronegativity FluorineFluorine (the reference element) is most electronegative, (the reference element) is most electronegative,

Cesium (Francium)Cesium (Francium) is least electronegative is least electronegative

Polarity of BondsPolarity of Bonds A covalent bond involves pairs of A covalent bond involves pairs of

electrons shared equally between electrons shared equally between two atomstwo atoms

How they are shared (equally or How they are shared (equally or unequally) depends on the electron unequally) depends on the electron donating and electron attracting donating and electron attracting nature of the atomsnature of the atoms

As the electronegativity difference As the electronegativity difference increases between two elements, increases between two elements, bond polarity increasesbond polarity increases

Polarity of BondsPolarity of Bonds Nonpolar (Pure) covalent bondNonpolar (Pure) covalent bond

• Two identical atoms will share the Two identical atoms will share the bonding electrons equallybonding electrons equally

Polar covalent bondPolar covalent bond• Two different atoms will not share the Two different atoms will not share the

bonding electrons equallybonding electrons equally• One atom will have a greater attraction One atom will have a greater attraction

for the shared pair than the other atomfor the shared pair than the other atom Ionic bondIonic bond

• Results from the transfer of one or more Results from the transfer of one or more electrons from one atom to anotherelectrons from one atom to another

ElectronegativityElectronegativity

Bond polarity measures the amount Bond polarity measures the amount of unequal sharing of electrons in a of unequal sharing of electrons in a chemical bondchemical bond

The difference in electronegativity The difference in electronegativity values determines the extent of values determines the extent of polarity in a bondpolarity in a bond

As the bond polarity increases, the As the bond polarity increases, the bond becomes more ionicbond becomes more ionic

ElectronegativityElectronegativity General guidelines related to electronegativity General guidelines related to electronegativity

differencesdifferences Bonds with a difference of zero are Bonds with a difference of zero are nonpolar nonpolar

(pure) covalent(pure) covalent Bonds with differences greater than 0.4 but less Bonds with differences greater than 0.4 but less

than 2.0 are called than 2.0 are called polar covalent bondspolar covalent bonds Bonds with differences 2.0 or greater are called Bonds with differences 2.0 or greater are called

ionicionic

MoleculeMolecule OO22 COCO MgMg22OOElectronegativity Electronegativity ValuesValues

3.5 and 3.53.5 and 3.5 2.5 and 3.52.5 and 3.5 1.2 and 3.51.2 and 3.5

Electronegativity Electronegativity DifferenceDifference 0.00.0 1.01.0 2.32.3Bond TypeBond Type Pure CovalentPure Covalent Polar CovalentPolar Covalent IonicIonic

ElectronegativityElectronegativity IncreasesIncreases across period (left to right) on Periodic Table across period (left to right) on Periodic Table DecreasesDecreases down group (top to bottom) on Periodic Table down group (top to bottom) on Periodic Table Larger difference in electronegativities means more polar Larger difference in electronegativities means more polar

bondbond• Negative end toward more electronegative atomNegative end toward more electronegative atom

MoleculeMolecule O-OO-O C-OC-O Mg-OMg-OElectronegativity Electronegativity ValuesValues

3.5 and 3.53.5 and 3.5 2.5 and 3.52.5 and 3.5 1.2 and 3.51.2 and 3.5

Electronegativity Electronegativity DifferenceDifference 0.00.0 1.01.0 2.32.3Bond TypeBond Type Pure CovalentPure Covalent Polar CovalentPolar Covalent IonicIonic

Polarity of Bonds/Dipole MomentsPolarity of Bonds/Dipole Moments

In a polar covalent bond: One of the In a polar covalent bond: One of the two different elements will inevitably two different elements will inevitably have a greater attraction for the have a greater attraction for the shared pair than the othershared pair than the other

This unequal sharing causes the This unequal sharing causes the entire molecule to behave like an entire molecule to behave like an electric dipole (electric dipole (dipole momentdipole moment))

Dipole: A body with two poles, one Dipole: A body with two poles, one partially negative and one positivepartially negative and one positive

Polar Bonds and Polar MoleculesPolar Bonds and Polar Molecules

Molecules (as well as bonds) can have Molecules (as well as bonds) can have polaritypolarity

A polar molecule has an unsymmetrical A polar molecule has an unsymmetrical distribution of electronic charge: The distribution of electronic charge: The bonding electrons are more attracted to bonding electrons are more attracted to one part of the molecule more than other one part of the molecule more than other partsparts

The polarity of a molecule has two factors:The polarity of a molecule has two factors: Bond polaritiesBond polarities Molecular geometryMolecular geometry

Fig11_5

H

O

H

(a) (b)

Center ofpositivecharge

Center ofnegativecharge

Polar Bonds and Polar MoleculesPolar Bonds and Polar Molecules If a molecule contains only polar bonds does If a molecule contains only polar bonds does

not mean the molecule as a whole is polarnot mean the molecule as a whole is polar Polarity will depend on whether or not the Polarity will depend on whether or not the

polarity effects cancel each otherpolarity effects cancel each other

Polar Bonds and Polar MoleculesPolar Bonds and Polar Molecules In a water molecule, In a water molecule,

oxygen draws the oxygen draws the shared pair of shared pair of electrons closer to electrons closer to oxygen and partially oxygen and partially withdrawn from withdrawn from hydrogenhydrogen

Since the dipoles do Since the dipoles do not cancel, water is a not cancel, water is a polarpolar molecule molecule

Since the dipoles do Since the dipoles do cancel, SOcancel, SO33 is a is a nonpolar nonpolar moleculemolecule

In a sulfur trioxide In a sulfur trioxide molecule, oxygen molecule, oxygen draws the shared pair draws the shared pair of electrons closer and of electrons closer and partially withdrawn partially withdrawn from sulfurfrom sulfur

Fig11_5

H

O

H

(a) (b)

Center ofpositivecharge

Center ofnegativecharge

Kinetic molecular theory of matter states that the particles present in any phase of matter are in constant, random motion: thermal energy

The thermal (kinetic) energy is temperature dependent

The particles interact together through attractions and repulsions that creates potential energy within the particles

Thermal (kinetic) and potential energy in a chemical system influence the chemical properties of a system

Kinetic energy gives the particles their motion and tends to move the particles away from each other

Potential energy is an attractive force which attracts the particles together

The relative influence of kinetic and potential energy is the main consideration when KM theory is used to explain the general properties of the gas, liquid, or solid states of matter

The type of energy that dominates will influence a substance’s physical state

Molecules in a liquid do not have all the same kinetic energy

These differences in energy are due to collisions between the molecules

The molecules near the surface, above the average KE, can escape the intermolecular forces holding them in the liquid phase

Interactions between Molecules

Intermolecular Forces are forces that act between a molecule and another molecule

They are electrostatic forces that are similar to the intramolecular forces involved in covalent bonding

Much weaker forces but strong enough to influence behavior of liquids

Properties of Liquids and Solids

The solid state is predominated by potential energy rather than by kinetic energy

Particles are in a fixed position by strong electrostatic attractions but vibrate due to kinetic energy

Definite volume and shape High density: the particles are

located as close as possible

Properties of Liquids and Solids In the liquid state is not dominated by potential

energy or by kinetic energy Particles are in not in a fixed position due to

kinetic energy and can slide over each other The potential energy (cohesive force) is strong

enough prevent total separation Assumes the shape of the container it occupies Definite volume and indefinite shape High density: the particles are not widely

separated but located as close as possible

Properties of Liquids and Solids In the gaseous state is dominated completely by

kinetic energy Particles of a gas are independent of each other

and move in a totally random manner due to their kinetic energy

The attractive forces between particles have been overcome by kinetic energy which allows particles to travel in all directions

Assumes both the volume and shape of the container it occupies

Indefinite volume and indefinite shape Low density: the particles are widely separated

and relatively few particles per unit volume

Properties of Liquids and Solids

Liquid and solid phases have many similar characteristics but gases are very different

The average distance between the particles only slightly different in the solid and liquid but vastly different in the gaseous state

Surface Tension and Viscosity In a liquid, surface tension arises when

molecules on the surface act like a thin membrane that allows objects to move on the surface liquid

Due to forces of attraction that bind them across the surface and pull them into the body of the liquid

This inward force causes the surface to contract to as small a surface as possible

Unlike the molecules within the body of the liquid that experience forces equally in all directions

Surface Tension and Viscosity

Surface tension results from an imbalance in forces of attraction

The magnitude of the surface tension of a liquid is affected by the strength of its intermolecular forces

Water has strong intermolecular forces and thus, very high surface tension

Surface Tension and Viscosity

Since liquids are incompressible and can flow, they assume the shape of their container

Some liquids easily flow and others do not (e.g. water vs. molasses)

Viscosity is a measure of a fluid’s resistance to flow

The stronger the intermolecular forces, the greater the resistance to flow

Attractive Forces in CompoundsAttractive Forces in Compounds

Intermolecular ForcesIntermolecular Forces• Ionic compounds: Ions (+ and -) Ionic compounds: Ions (+ and -)

are held together by ionic bondsare held together by ionic bonds• Neutral molecules: One or more of Neutral molecules: One or more of

these forces hold molecules these forces hold molecules together in liquids and solids:together in liquids and solids:

• Dipole-dipoleDipole-dipole• Hydrogen-bondingHydrogen-bonding• DispersionDispersion

Attractive Forces in CompoundsAttractive Forces in Compounds Dipole-dipoleDipole-dipole: Attractions between polar : Attractions between polar

moleculesmolecules The nonsymmetrical distribution of the charge The nonsymmetrical distribution of the charge

causes the molecules to line up causes the molecules to line up Positive end of one directed toward negative end Positive end of one directed toward negative end

of otherof other

Attractive Forces in CompoundsAttractive Forces in Compounds

Hydrogen bondingHydrogen bonding: A special type of dipole-dipole : A special type of dipole-dipole interactioninteraction

Occurs between molecules that have a H atom Occurs between molecules that have a H atom bonded to bonded to F, O, or NF, O, or N

The partially positive H and a lone pair of electrons on The partially positive H and a lone pair of electrons on another N, O, or F atomanother N, O, or F atom

Attractive Forces in CompoundsAttractive Forces in Compounds Dispersion (London) forces: Short-lived dipoles caused by Dispersion (London) forces: Short-lived dipoles caused by

uneven shifts in electron densityuneven shifts in electron density The uneven shift causes one end of the molecule to be slightly The uneven shift causes one end of the molecule to be slightly

positive and one end slightly negativepositive and one end slightly negative This induces the same electron shift in adjacent molecules This induces the same electron shift in adjacent molecules

which causes an attractive forcewhich causes an attractive force Only intermolecular force possible in nonpolar substancesOnly intermolecular force possible in nonpolar substances

Matter and Changes of StateMatter and Changes of State

Matter: Anything Matter: Anything that has mass and that has mass and occupies spaceoccupies space

It is separated into It is separated into three categories: three categories: Solid, Liquid, and Solid, Liquid, and GasGas

Matter and Changes of StateMatter and Changes of State

A change in state is the most A change in state is the most common type of physical changecommon type of physical change• Melting/FreezingMelting/Freezing• Vaporization/CondensationVaporization/Condensation• Sublimation/DepositionSublimation/Deposition

The composition of the substance The composition of the substance does not change, only its appearancedoes not change, only its appearance

MeltingMelting/Freezing/Freezing A change of state requiring the input of heatA change of state requiring the input of heat Heat of FusionHeat of Fusion

• Heat energy required to Heat energy required to melt melt 1 g 1 g of a of a substance substance

• Heat energy that must be removed to Heat energy that must be removed to freeze 1 gfreeze 1 g of a substance of a substance

• Heat energy (to melt) 1 g of ice Heat energy (to melt) 1 g of ice ((waterwater at 0 °C): at 0 °C):

gJ334 fusionofheat water

Change of State ProblemChange of State Problem

Calculate the heat Calculate the heat needed (in Joules) to needed (in Joules) to melt 15 g of ice at melt 15 g of ice at 0°C, and to heat the 0°C, and to heat the water to 75 °Cwater to 75 °C

Two parts to the Two parts to the problemproblem• Melt ice (use Melt ice (use heat heat

of fusionof fusion for water) for water)• Heat water (use Heat water (use

specific heatspecific heat of of Water)Water)

Change of State ProblemChange of State Problem Melt the iceMelt the ice Calculate the heat absorbed to melt the ice Calculate the heat absorbed to melt the ice

at 0 °C (no change in temperature)at 0 °C (no change in temperature)

gJ 334 g 15

g

J334ΔH fus

J 5010

Change of State ProblemChange of State Problem Heat the waterHeat the water Calculate the heat energy needed to warm the water from Calculate the heat energy needed to warm the water from

0 °C to 75 °C0 °C to 75 °C

J 4710

Cg

J4.184SH OH2

g15.0Cg

J 4.184

)C0C75 (

Δt(g)massSH OH2

(75 °C)

Change of State ProblemChange of State ProblemCombining Energy CalculationsCombining Energy Calculations

Calculate the total heatCalculate the total heat• Melting the ice (QMelting the ice (Q11))

• Heating the water (QHeating the water (Q22)

J9,720Qtotal

J 5,010 Q1

J4,710Q2

total21 QQQ

Change of State Change of State

Sublimation: A phase change from solid to gas Sublimation: A phase change from solid to gas without going through the liquid statewithout going through the liquid state• Requires the absorption of heatRequires the absorption of heat• No temperature change occurs during processNo temperature change occurs during process• Deposition is the reverse process (heat is released)Deposition is the reverse process (heat is released)

Evaporation: A phase change from a liquid to a Evaporation: A phase change from a liquid to a gasgas• Requires the absorption of heatRequires the absorption of heat• No temperature change occurs during processNo temperature change occurs during process• Condensation is the reverse process (heat is Condensation is the reverse process (heat is

released)released)

Change of State Change of State Boiling: A special form of evaporation where Boiling: A special form of evaporation where

the liquid converts to vapor through bubble the liquid converts to vapor through bubble formationformation

Boiling point: Temp at which the vapor Boiling point: Temp at which the vapor pressure of the liquid is the same as the pressure of the liquid is the same as the atmospheric pressureatmospheric pressure

This allows the bubbles at the liquid surface This allows the bubbles at the liquid surface to escape in the atmosphereto escape in the atmosphere

VaporizationVaporization/Condensation/Condensation Heat of VaporizationHeat of Vaporization

• Heat energy required to Heat energy required to vaporizevaporize 1 g 1 g of a substance of a substance

• Heat energy that must be removed Heat energy that must be removed to to condense 1 gcondense 1 g of a substance of a substance

• Heat energy (to vaporize) 1 g of Heat energy (to vaporize) 1 g of water to vapor:water to vapor:

gJ2260 onvaporizatiofheat water

Change of State ProblemChange of State ProblemCalculate the heat needed Calculate the heat needed

(in Joules) to heat 15 g (in Joules) to heat 15 g of water from 75 °C to of water from 75 °C to 100 °C, and to convert it 100 °C, and to convert it to steam at 100 °Cto steam at 100 °C

Two parts to the Two parts to the problemproblem• Heat the water (use Heat the water (use

specific heatspecific heat for for water)water)

• Convert water to Convert water to steam (usesteam (use heat heat of of vaporization for vaporization for Water)Water)

Change of State ProblemChange of State Problem Heat the waterHeat the water Calculate the heat energy needed to warm the water from Calculate the heat energy needed to warm the water from

75 °C to 100 °C75 °C to 100 °C

J 1570

Cg

J4.184SH OH2

g15.0Cg

J 4.184

)( CC 75100

Δt(g)massSH OH2

×25 °C

Change of State ProblemChange of State Problem Calculate the heat absorbed to convert the Calculate the heat absorbed to convert the

liquid water to steam at 100 °C (no change liquid water to steam at 100 °C (no change in temperature)in temperature)

J33,900 g 15.0

g

J2260ΔHvap

g

J2260

Change of State ProblemChange of State ProblemCombining Energy CalculationsCombining Energy Calculations

Calculate the total heatCalculate the total heat• Heat the water (QHeat the water (Q11))

• Convert liquid water to steam (QConvert liquid water to steam (Q22)

J35,500Qtotal

J 1,570 Q1

J33,900Q2

total21 QQQ

Heats of Fusion and VaporizationHeats of Fusion and Vaporization

Heating CurveHeating Curve

Illustrates the steps involved in changing a Illustrates the steps involved in changing a solid to a gassolid to a gas• Heat added is shown on the x-axisHeat added is shown on the x-axis• Temperature is shown on the y-axisTemperature is shown on the y-axis

Energy required to undergo a series of Energy required to undergo a series of phase changes depends on the (three) phase changes depends on the (three) property values of the substance:property values of the substance:• Specific HeatSpecific Heat• Heat of FusionHeat of Fusion• Heat of VaporizationHeat of Vaporization

Heating CurveHeating Curve

No temp change

No temp change

endend

Sharing Electrons Between Atoms Sharing Electrons Between Atoms of Different Elementsof Different Elements

Two nonidentical Two nonidentical nonmetal atomsnonmetal atoms

The number of The number of covalent bonds an covalent bonds an atom forms will equal atom forms will equal the number of the number of electrons needed to electrons needed to form a form a noble gas noble gas configurationconfiguration

Each Each vacancy + vacancy + unpaired electronunpaired electron combination in the combination in the valence shell can be valence shell can be used to form a two-used to form a two-electron bond electron bond

Each atom will share Each atom will share valence electrons with valence electrons with the other forming a the other forming a shared pair of bonding shared pair of bonding electrons (achieves a electrons (achieves a stable stable noble gas noble gas configuration)configuration)

Covalent Lewis Structures:Covalent Lewis Structures:Double and Triple Bonds BondingDouble and Triple Bonds Bonding

Single BondSingle Bond• Uses a single pair of electrons between two Uses a single pair of electrons between two

atomsatoms Double BondDouble Bond

• Uses two pairs of electrons between the Uses two pairs of electrons between the same two atomssame two atoms

Triple BondTriple Bond• Uses three pairs of electrons between the Uses three pairs of electrons between the

same two atomssame two atoms

NNOOF F

Writing Resonance StructuresWriting Resonance Structures Example: Write a Lewis structure for nitrate ion and include resonance Example: Write a Lewis structure for nitrate ion and include resonance

structuresstructures Use a double-headed arrow to connect the structures Use a double-headed arrow to connect the structures

NO

OO

-

NO

OO

-

NO

OO

-


The reaction of sodium and chlorineThe reaction of sodium and chlorine The reaction represented through dot The reaction represented through dot

structures:structures:

Na• + :Cl: Li1+[:F:]1-

•

•• ••

••

ResonanceResonance

Resonance occurs whenever it is possible Resonance occurs whenever it is possible to draw two or more electron-dot to draw two or more electron-dot structuresstructures

They differ only in the location of a They differ only in the location of a double bond between the same two double bond between the same two types of atomstypes of atoms

Two of the four electrons in the double Two of the four electrons in the double bond rapidly move between the two bond rapidly move between the two single bonds: The true structure is the single bonds: The true structure is the average of the individual structuresaverage of the individual structures

Chapter 10 Molecular Structure: Solids and Liquids.

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Transcript of Chapter 10 Molecular Structure: Solids and Liquids.