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Introductory Chemistry , 2 nd Edition Nivaldo Tro. Chapter 10 Chemical Bonding. Bonding Theories. Chemical bonding describes way atoms attach to make compounds Understanding of bonding allows chemists to: predict shapes of molecules and properties of substances - PowerPoint PPT Presentation
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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
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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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:
• •
•
• • • •
•• •• •• ••
••
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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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?
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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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
•
•• ••
••
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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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).
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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
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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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
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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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
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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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
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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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
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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
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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
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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
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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
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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”
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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
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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••
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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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 -
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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
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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ElectronegativityElectronegativity
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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
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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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
Tro's Introductory Chemistry, Chapter 1Tro's Introductory Chemistry, Chapter 100
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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
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:: 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
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CH2Cl2
= 2.0 D CCl4
= 0.0 D
C
Cl
ClCl
Cl
C
Cl
ClH
H
Polar or Nonpolar Molecule?Polar or Nonpolar Molecule?