introductory chemistry , 2 nd edition nivaldo tro

Introductory ChemistryIntroductory Chemistry, 2, 2ndnd Edition EditionNivaldo TroNivaldo Tro

Chapter 10ChemicalBonding

Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100

22

Bonding TheoriesBonding Theories

Chemical bonding describes way atoms Chemical bonding describes way atoms attach to make compoundsattach to make compounds

Understanding of bonding allows chemists Understanding of bonding allows chemists to: to:

1)1) predict shapes of molecules and predict shapes of molecules and properties of substances properties of substances

2)2) design and build molecules with particular design and build molecules with particular sets of chemical and physical propertiessets of chemical and physical properties


33

LewisLewis Symbols of Atoms Symbols of AtomsAlso known as Also known as electron dotelectron dot symbols symbols

Symbol of element represents nucleus Symbol of element represents nucleus and inner electronsand inner electrons

Valence electrons are dotsValence electrons are dots in imaginary 4 in imaginary 4 sides around symbol sides around symbol – put one electron on each side first, then pairput one electron on each side first, then pair

Elements in Elements in same group have same same group have same number of valence electronsnumber of valence electrons; therefore ; therefore their Lewis dot symbols will look aliketheir Lewis dot symbols will look alike

Li• Be• •B• •C• •N• •O: :F: :Ne:

• •

•

• • • •

•• •• •• ••

••


44

Lewis Bonding TheoryLewis Bonding TheoryAtoms Atoms bondbond because it results in a because it results in a more stable electron configurationmore stable electron configurationAtoms bond together by Atoms bond together by – transferring electrons (ionic bond)transferring electrons (ionic bond) or or – sharing electrons (covalent bond)sharing electrons (covalent bond) so so

that all atoms obtain an outer shell with that all atoms obtain an outer shell with 8 electrons = 8 electrons = Octet RuleOctet Rule

– there are exceptions to this rule – the there are exceptions to this rule – the key to remember is to try to get a key to remember is to try to get a valence electron configuration like a valence electron configuration like a noble gasnoble gas

– Which noble gas is an exception? Which noble gas is an exception? He, why?He, why?


55

Lewis Symbols of IonsLewis Symbols of IonsCationsCations have Lewis symbols have Lewis symbols without without valence electronsvalence electrons– Lost in the cation formationLost in the cation formation

AnionsAnions have Lewis symbols with have Lewis symbols with 8 8 valence electronsvalence electrons– Electrons gained in the formation of the Electrons gained in the formation of the

anionanion

Li• Li+1 :F: → [:F:]-1

•

•• ••

••


66

What determines which type of What determines which type of bond is formedbond is formed??

ElectronegativityElectronegativity = attraction for = attraction for electronselectrons

ionic bondionic bond: two atoms have a large : two atoms have a large difference in electronegativity.difference in electronegativity.

covalent bondcovalent bond: atoms have similar : atoms have similar electronegativitieselectronegativities

77

Ionic bond: very different Ionic bond: very different electronegativitieselectronegativities

I would do anything

for an e- !!!I really don’t

want this electron…

Metals = give up electrons easily; become +

Non-metals = like to gain electrons become -

Metal(+) and non-metal(-) = ionic bond will be formed (not covalent).

88

Covalent bond: similar Covalent bond: similar electronegativitieselectronegativities

We could share the

electrons we have!

We seem to both want to

keep our electrons… How can we get octets?

2 non-metals = covalent bond will be formed (not ionic).


99

Ionic BondsIonic Bonds

Metal transfers electron(s) to nonmetalMetal transfers electron(s) to nonmetal

Metal losesMetal loses electrons to form electrons to form cationcation

Nonmetal gainsNonmetal gains electrons to form electrons to form anionanion

Ionic bondIonic bond results from results from ++ to to - - attractionattraction– larger charge = stronger attractionlarger charge = stronger attraction

– smaller ion = stronger attractionsmaller ion = stronger attraction

Lewis Theory allows us to predict the Lewis Theory allows us to predict the correct formulas of ionic compoundscorrect formulas of ionic compounds

1010

Example: ionic bondExample: ionic bond

ClNa

1111

Example: ionic bond

Na Cl

Na Cl-+

1212

Charges of ions:Charges of ions:

If an atom:If an atom: Its charge is now:Its charge is now:

loses an eloses an e-- +1+1

gains an egains an e-- -1 -1

loses 2 eloses 2 e-- +2+2

gains 2 egains 2 e-- -2 -2

1313

Draw Lewis structure for compound Draw Lewis structure for compound formed between Mg and O.formed between Mg and O.

Mg O

-2+2

xxxx

magnesium oxide

1414

Draw Lewis structures for the Draw Lewis structures for the compounds formed by:compounds formed by:

sodium & sulfursodium & sulfur

calcium & brominecalcium & bromine

1515

sodium & sulfurNa2S

calcium & bromineCaBr2 Ca Br

-+2

xxBr

-xx

-2

Na+

S xxNa+

xx

Name these!Name these!

sodium sulfide

calcium bromide

1616

Covalent BondsCovalent Bonds = sharing of = sharing of electronselectrons

Type of bond for Type of bond for two two nonmetalnonmetal atoms atoms

Attraction for electrons (Attraction for electrons (electronegativityelectronegativity) ) is similar for both atoms involvedis similar for both atoms involved

H Hxx

HH xx

HH22


1717

Covalent BondsCovalent Bonds

Formed between Formed between two nonmetalstwo nonmetals Atoms bonded together to form Atoms bonded together to form moleculesmolecules– strong attractionstrong attraction

SharingSharing pairs of electrons to attain pairs of electrons to attain octetsoctetsMolecules generally weakly attracted to Molecules generally weakly attracted to each othereach other– observed physical properties of molecular observed physical properties of molecular

substance due to these attractionssubstance due to these attractions

1818

Cl - Cl

Shared electrons are always in pairs.

single bond = one shared pair of electrons

Cl Cl

Cl Cl

ClCl22


1919

Single Covalent BondsSingle Covalent Bonds

Two atoms share one pair of electronsTwo atoms share one pair of electrons– 2 electrons2 electrons

One atom may have more than one single One atom may have more than one single bondbond

F••

••

•• • F•••••••

HF••

••

•• ••

••F•••• H O

•• ••••

••

H•H• O••

• •

••

F F

2020

Write the Lewis structure for CHWrite the Lewis structure for CH44

HCH

H

H

How many single bonds does it have?

HCH

H

Hbond line formula

4


2121

Double Covalent BondDouble Covalent BondTwo atoms sharing two pairs of electronsTwo atoms sharing two pairs of electrons– 4 electrons4 electrons

Shorter and stronger than single bond Shorter and stronger than single bond

O••••O••

••••••

O••

• •

••O••

• •

••

O O


2222

Triple Covalent BondTriple Covalent Bond

Two atoms sharing 3 pairs of electronsTwo atoms sharing 3 pairs of electrons– 6 electrons6 electrons

Shorter and stronger than single or Shorter and stronger than single or double bonddouble bond

N••

•

•

•N••

•

•

•

N•••••••••• N

N N

2323

Ionic or Covalent? and Name?Ionic or Covalent? and Name?

NaClNaCl

MgBrMgBr

PHPH33

NONO

KNOKNO33

Mg(OH)Mg(OH)22

NHNH44BrBr

HH22OO

ionic sodium chloride

ionic magnesium bromide

covalent phosphorus trihydride

ionic potassium nitrate

ionic magnesium hydroxide

ionic ammonium bromide

covalent dihydrogen monoxide

covalent nitrogen monoxide


2424

Ionic or Covalent? Write the Ionic or Covalent? Write the formula:formula:

ammonium sulfideammonium sulfide

dihydrogen dioxidedihydrogen dioxide

potassium sulfatepotassium sulfate

copper copper IIII nitrate nitrate

ionic (NH4)2S

covalent H2O2

ionic K2SO4

ionic Cu(NO3)2


2525

Exceptions to the Octet RuleExceptions to the Octet Rule

H & Li, lose one electron to form cationH & Li, lose one electron to form cation

– Li now has electron configuration like He Li now has electron configuration like He

– H can also share or gain one electron to have H can also share or gain one electron to have configuration like Heconfiguration like He

Be shares 2 electrons to form two single Be shares 2 electrons to form two single bondsbonds

B shares 3 electrons to form three single B shares 3 electrons to form three single bondsbonds


2626

Exceptions to the Octet RuleExceptions to the Octet Rule

Expanded octets for elements in Period 3 or Expanded octets for elements in Period 3 or belowbelow

– using empty valence using empty valence dd orbitals orbitals

Some molecules have odd numbers of Some molecules have odd numbers of electronselectrons– NONO

:: ON


2727

Molecular GeometryMolecular Geometry

Molecules are 3-dimensional objectsMolecules are 3-dimensional objects

Describe shape of a molecule with terms Describe shape of a molecule with terms that relate to geometric figuresthat relate to geometric figures

These geometric figures have These geometric figures have characteristic characteristic “corners”“corners” that indicate that indicate positions of surrounding atoms with positions of surrounding atoms with central atom in center of the figurecentral atom in center of the figure

The geometric figures also have The geometric figures also have characteristic angles that we call characteristic angles that we call bond bond anglesangles


2828

Some Geometric FiguresSome Geometric FiguresLinearLinear– 2 atoms on opposite sides of 2 atoms on opposite sides of

central atomcentral atom– 180° bond angles180° bond angles

Trigonal PlanarTrigonal Planar– 3 atoms form a triangle around the 3 atoms form a triangle around the

central atomcentral atom– Planar, 120° bond angles Planar, 120° bond angles

TetrahedralTetrahedral– 4 surrounding atoms form a 4 surrounding atoms form a

tetrahedron around central atomtetrahedron around central atom– 109.5° bond angles109.5° bond angles

180°

120°

109.5°

2929

Predicting Molecular Shape: Predicting Molecular Shape: VSEPRVSEPR

VValence alence SShell hell EElectron lectron PPair air RRepulsion epulsion Theory = the shape of a molecule can be Theory = the shape of a molecule can be predicted by assuming that the electron predicted by assuming that the electron pairs repel each other.pairs repel each other.

HCH

H

HHow will the electrons How will the electrons distribute themselves distribute themselves around C in order to be around C in order to be as far as possible away as far as possible away from each other?from each other?

3030

Tetrahedral Distribution of Tetrahedral Distribution of Four Electron PairsFour Electron Pairs

3131

Central Atom with 4 electron pairs Central Atom with 4 electron pairs bonded to 4 atoms in cornersbonded to 4 atoms in corners

CHCH4 4 == molecule is molecule is

“tetrahedral”“tetrahedral”

3232

What would be the shape of What would be the shape of these molecules?these molecules?

NH

H H

O H

H

3333

““pyramidal”pyramidal”

““bent”bent”

NH

H H

O H

H

3434

When there are only two atoms, the When there are only two atoms, the only molecular shape possible is:only molecular shape possible is:

O

H-1

“linear”


3535

Linear ShapesLinear Shapes

LinearLinear– 2 areas of electrons 2 areas of electrons

around the central atom, around the central atom, both bondingboth bonding

Or two atom molecule Or two atom molecule

– 180° Bond Angles180° Bond Angles

:: OCO


3636

Bond PolarityBond PolarityUnequal sharingUnequal sharing of electrons between of electrons between unlike unlike atomsatoms– one atom pulls electrons in the bond closer to one atom pulls electrons in the bond closer to

its sideits side

– one end of the bond has one end of the bond has larger electron densitylarger electron density than the otherthan the other

The end with the larger electron density gets a The end with the larger electron density gets a partial negativepartial negative charge and the end that is charge and the end that is electron deficient gets a electron deficient gets a partial positivepartial positive charge charge

H Cl••


3737

ElectronegativityElectronegativityAttraction an atom has for bonding electrons Attraction an atom has for bonding electrons in covalent bondin covalent bond

Increases across period (left to right)Increases across period (left to right)

Decreases down group (top to bottom)Decreases down group (top to bottom)

Larger difference in electronegativity, more Larger difference in electronegativity, more polar the bondpolar the bond– negative end toward more electronegative atomnegative end toward more electronegative atom

+ H — F -


3838

ElectronegativityElectronegativity

2.1

1.0

0.9

0.8

0.8

0.7

0.7

1.5

1.2

1.0

1.0

0.9

0.9

1.3

1.2

1.1

1.1

1.5

1.4

1.3

1.6

1.6

1.5

1.6

1.8

1.7

1.5

1.9

1.9

1.8

2.2

2.2

1.8

2.2

2.2

1.8

2.2

2.2

1.9

1.9

2.4

1.6

1.7

1.9

2.0

1.5

1.6

1.7

1.8

2.5 3.0 3.5 4.0

1.8

2.1 2.5 3.0

1.8

1.8

1.8

2.0

1.9

1.9

2.4

2.1

2.0

2.8

2.5

2.2


3939

ElectronegativityElectronegativity


4040

Electronegativity & Bond PolarityElectronegativity & Bond Polarity

Nonpolar covalent = Nonpolar covalent = difference in difference in electronegativity between bonded atoms electronegativity between bonded atoms is is 0 to 0.30 to 0.3

Polar covalentPolar covalent == difference in difference in electronegativity between bonded atoms electronegativity between bonded atoms is is 0.4 to 1.90.4 to 1.9

Ionic =Ionic = difference in electronegativity difference in electronegativity between bonded atoms larger than or between bonded atoms larger than or equal to equal to 2.02.0


4141

Bond PolarityBond Polarity

0 0.4 2.0 4.0Electronegativity Electronegativity DifferenceDifference

covalentcovalent ionicionic

polarpolarnonnon

polarpolar

3.0-3.03.0-3.0= 0.0= 0.0

4.0-2.14.0-2.1= 1.9= 1.9

3.0-0.93.0-0.9= 2.1= 2.1


4242

Polarity of Polarity of MoleculesMolecules

For a For a moleculemolecule to be polar it must to be polar it must1)1) have polar have polar bondsbonds

electronegativity difference of 0.4 – 1.9electronegativity difference of 0.4 – 1.9

bond dipole moments - measuredbond dipole moments - measured

2)2) have an unsymmetrical shapehave an unsymmetrical shape

Polarity affects the Polarity affects the intermolecular intermolecular forces of attractionforces of attraction


4343

:: OCO

polar bondspolar bonds,but nonpolar nonpolar

moleculemoleculebecause pulls cancel pulls cancel

OH H

polar bondspolar bonds,and unsymmetricalunsymmetrical

shape causes moleculemoleculeto be polarpolar

Polarity of Polarity of MoleculesMolecules


4444

CH2Cl2

= 2.0 D CCl4

= 0.0 D

C

Cl

ClCl

Cl

C

Cl

ClH

H

Polar or Nonpolar Molecule?Polar or Nonpolar Molecule?

introductory chemistry , 2 nd edition nivaldo tro

Documents

electrons ionic bond

electrons covalent bond

electrons electronegativity

electronsionic bond

type of bond

lewis bonding theoryatoms

number of valence electrons

cationnonmetal gains