of 90
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Chapter 9
Chemical
Bonding I:
Lewis Theory
2008, Prentice Hall
Chemistry: A Molecular Approach, 1stEd.
Nivaldo Tro
Roy Kennedy
Massachusetts Bay Community College
Wellesley Hills, MA
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Tro, Chemistry: A Molecular Approach 2
Bonding Theories explain how and why atoms attach together
explain why some combinations of atoms are stableand others are notwhy is water H2O, not HO or H3O
one of the simplest bonding theories was developed by
G.N. Lewis and is called Lewis Theory Lewis Theory emphasizes valence electrons to explain
bonding
using Lewis Theory, we can draw modelscalledLewis structuresthat allow us to predict many
properties of molecules
aka Electron Dot Structures
such as molecular shape, size, polarity
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Tro, Chemistry: A Molecular Approach 3
Why Do Atoms Bond? processes are spontaneous if they result in a system
with lower potential energy
chemical bonds form because they lower the potential
energy between the charged particles that composeatoms
the potential energy between charged particles isdirectly proportional to the product of the charges
the potential energy between charged particles isinversely proportional to the distance between thecharges
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Tro, Chemistry: A Molecular Approach 4
Potential Energy Between
Charged Particles
0is a constant= 8.85 x 10-12C2/Jm
for charges with the same sign, Epotentialis + and themagnitude gets less positive as the particles get fartherapart
for charges with the opposite signs, Epotentialis and
the magnitude gets more negative as the particles getcloser together
remember: the more negative the potential energy, themore stable the system becomes
r
qq 21
0potential
4
1E
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Tro, Chemistry: A Molecular Approach 5
Potential Energy Between
Charged Particles
The repulsion between
like-charged particles
increases as theparticles get closer
together. To bring
them closer requires
the addition of moreenergy.
The attraction between
opposite-charged
particles increases asthe particles get closer
together. Bringing
them closer lowers the
potential energy of thesystem.
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Tro, Chemistry: A Molecular Approach 6
Bonding
a chemical bond forms when the potentialenergy of the bonded atoms is less than the
potential energy of the separate atoms have to consider following interactions:nucleus-to-nucleus repulsion
electron-to-electron repulsionnucleus-to-electron attraction
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Tro, Chemistry: A Molecular Approach 7
Types of Bonds
Types of Atoms Type of BondBond
Characteristic
metals to
nonmetals Ionicelectrons
transferred
nonmetals to
nonmetalsCovalent
electrons
shared
metal to
metalMetallic
electrons
pooled
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8
Types of Bonding
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Ionic Bonds
when metals bond to nonmetals, some electronsfrom the metal atoms are transferred to the
nonmetal atomsmetals have low ionization energy, relatively easy to
remove an electron from
nonmetals have high electron affinities, relativelygood to add electrons to
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Covalent Bonds nonmetals have relatively high ionization energies, so it
is difficult to remove electrons from them
when nonmetals bond together, it is better in terms ofpotential energy for the atoms to share valenceelectrons
potential energy lowest when the electrons are between thenuclei
shared electrons hold the atoms together by attractingnuclei of both atoms
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Tro, Chemistry: A Molecular Approach 12
Lewis Symbols of Atoms
aka electron dot symbols use symbol of element to represent nucleus and
inner electrons
use dots around the symbol to represent valenceelectrons
pair first two electrons for thesorbital
put one electron on each open side forpelectrons
then pair rest of thepelectrons
LiBe
B
C
N
O
F
Ne
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Tro, Chemistry: A Molecular Approach 13
Lewis Symbols of Ions
Cations have Lewis symbols withoutvalence electrons
Lost in the cation formation
Anions have Lewis symbols with 8 valenceelectrons
Electrons gained in the formation of the anion
Li Li+1
F
1
F
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Tro, Chemistry: A Molecular Approach 15
Stable Electron Arrangements
And Ion Charge Metals form cations by losing
enough electrons to get thesame electron configurationas the previous noble gas
Nonmetals form anions bygaining enough electrons toget the same electronconfiguration as the next
noble gas The noble gas electronconfiguration must be verystable
Atom Atoms
Electron
Config
Ion Ions
Electron
ConfigNa [Ne]3s
1Na
+1[Ne]
Mg [Ne]3s2 Mg
+2 [Ne]
Al [Ne]3s23p
1Al
+3 [Ne]
O [He]2s22p4 O-2 [Ne]
F [He]2s22p
5 F
-1[Ne]
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Tro, Chemistry: A Molecular Approach 16
Octet Rule when atoms bond, they tend to gain, lose, or share electrons to
result in 8 valence electrons
ns2np6 noble gas configuration
many exceptions H, Li, Be, B attain an electron configuration like He
He = 2 valence electrons
Li loses its one valence electronH shares or gains one electron
though it commonly loses its one electron to become H+
Be loses 2 electrons to become Be2+ though it commonly shares its two electrons in covalent bonds, resulting in 4
valence electrons
B loses 3 electrons to become B3+
though it commonly shares its three electrons in covalent bonds, resulting in 6valence electrons
expanded octets for elements in Period 3 or below using empty valence dorbitals
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Tro, Chemistry: A Molecular Approach 17
Lewis Theory
the basis of Lewis Theory is that there arecertain electron arrangements in the atom thatare more stable
octet rule
bonding occurs so atoms attain a more stableelectron configuration
more stable = lower potential energyno attempt to quantify the energy as the calculation
is extremely complex
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Tro, Chemistry: A Molecular Approach 18
Properties of Ionic Compounds
hard and brittle crystalline solidsall are solids at room temperature
melting points generally > 300C the liquid state conducts electricitythe solid state does not conduct electricity
many are soluble in waterthe solution conducts electricity well
Melting an Ionic Solid
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Tro, Chemistry: A Molecular Approach 19
Conductivity of NaCl
in NaCl(s), the
ions are stuck in
position and not
allowed to moveto the charged
rods
in NaCl(aq), the
ions are
separated andallowed to move
to the charged
rods
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Tro, Chemistry: A Molecular Approach 20
Lewis Theory and Ionic Bonding
Lewis symbols can be used to represent thetransfer of electrons from metal atom to
nonmetal atom, resulting in ions that areattracted to each other and therefore bond
FLi +
1
F
Li +
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Tro, Chemistry: A Molecular Approach 21
Predicting Ionic Formulas
Using Lewis Symbols electrons are transferred until the metal loses all its
valence electrons and the nonmetal has an octet
numbers of atoms are adjusted so the electron transfercomes out even
O
Li
Li
2
O2 Li + Li2O
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Tro, Chemistry: A Molecular Approach 22
Energetics of Ionic Bond Formation
the ionization energy of the metal is endothermicNa(s) Na+(g) + 1 e DH= +603 kJ/mol
the electron affinity of the nonmetal is exothermicCl2(g) + 1 e
Cl(g) DH= 227 kJ/mol
generally, the ionization energy of the metal is largerthan the electron affinity of the nonmetal, therefore theformation of the ionic compound should beendothermic
but the heat of formation of most ionic compounds isexothermic and generally large; Why?
Na(s) + Cl2(g) NaCl(s) DHf = -410 kJ/mol
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Tro, Chemistry: A Molecular Approach 23
Ionic Bonds
electrostatic attraction is nondirectional!!no direct anion-cation pair
no ionic molecule
chemical formula is an empirical formula, simplygiving the ratio of ions based on charge balance
ions arranged in a pattern called a crystal lattice
every cation surrounded by anions; and every anionsurrounded by cations
maximizes attractions between + and - ions
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Tro, Chemistry: A Molecular Approach 24
Lattice Energy the lattice energyis the energy released when the
solid crystal forms from separate ions in the gas state always exothermic
hard to measure directly, but can be calculated fromknowledge of other processes
lattice energy depends directly on size of charges andinversely on distance between ions
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Tro, Chemistry: A Molecular Approach 25
Born-Haber Cycle
method for determining the lattice energy of anionic substance by using other reactions
use Hesss Law to add up heats of other processes
DHf
(salt) = DHf
(metal atoms, g) + DHf
(nonmetal atoms, g)
+ DHf(cations, g) + DHf(anions, g) + DHf(crystal lattice)
DHf(crystal lattice) = Lattice Energy
metal atoms (g) cations (g), DHf= ionization energy
dont forget to add together all the ionization energies to get to thedesired cation
M2+= 1stIE + 2ndIE
nonmetal atoms (g) anions (g), DHf= electron affinity
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Tro, Chemistry: A Molecular Approach 26
Born-Haber Cycle for NaCl
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Tro, Chemistry: A Molecular Approach 28
Practice - Given the Information Below,
Determine the Lattice Energy of MgCl2
Mg(s) Mg(g) DH1f= +147.1 kJ/mol Cl2(g) Cl(g) DH2f= +121.3 kJ/mol
Mg(g) Mg+1(g) DH3f= +738 kJ/mol
Mg+1(g) Mg+2(g) DH4f= +1450 kJ/mol
Cl(g) Cl-1(g) DH5f= -349 kJ/mol
Mg(s) + Cl2(g) MgCl2(s) DH6f= -641.3 kJ/mol
kJ2521H
kJ)2(-349kJ)1450(kJ)738(kJ)121.3(2kJ)147.1(-kJ)3.641(H
H2HHH2HHH
HH2HHH2HH
energylatticef
energylatticef
f5f4f3f2f1f6energylatticef
energylatticeff5f4f3f2f1f6
DD
DDDDDDD
DDDDDDD
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Tro, Chemistry: A Molecular Approach 29
Trends in Lattice Energy
Ion Size
the force of attraction between chargedparticles is inversely proportional to the
distance between them
larger ions mean the center of positive charge(nucleus of the cation) is farther away from
negative charge (electrons of the anion)
larger ion = weaker attraction = smaller lattice
energy
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Tro, Chemistry: A Molecular Approach 30
Lattice Energy vs.
Ion Size
Metal ChlorideLattice Energy
(kJ/mol)
LiCl -834
NaCl -787
KCl -701
CsCl -657
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Tro, Chemistry: A Molecular Approach 31
Trends in Lattice Energy
Ion Charge
the force of attraction betweenoppositely charged particles is
directly proportional to the product
of the charges larger charge means the ions aremore strongly attracted
larger charge = stronger attraction =
larger lattice energy
of the two factors, ion chargegenerally more important
Lattice Energy =
-910 kJ/mol
Lattice Energy =
-3414 kJ/mol
Example 9 2 Order the following ionic
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Tro, Chemistry: A Molecular Approach 32
Example 9.2Order the following ionic
compounds in order of increasing magnitude of
lattice energy.
CaO, KBr, KCl, SrO
First examine the ion charges and
order by product of the chargesCa2+& O2-, K+& Br,
K+& Cl, Sr2+& O2
(KBr, KCl) < (CaO, SrO)
Then examine the ion sizes of
each group and order by radius;
larger < smaller
(KBr, KCl) same cation,
Br> Cl(same Group)
KBr < KCl < (CaO, SrO)
(CaO, SrO) same anion,
Sr2+> Ca2+(same Group)
KBr < KCl < SrO < CaO
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Tro, Chemistry: A Molecular Approach 33
Ionic Bonding
Model vs. Reality ionic compounds have high melting points and boiling
points
MP generally > 300C
all ionic compounds are solids at room temperature
because the attractions between ions are strong,breaking down the crystal requires a lot of energy
the stronger the attraction (larger the lattice energy), thehigher the melting point
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Tro, Chemistry: A Molecular Approach 34
Ionic Bonding
Model vs. Reality
ionic solids are brittle and hard the position of the ion in the crystal is critical to
establishing maximum attractive forcesdisplacing the ions from their positions resultsin like charges close to each other and therepulsive forces take over
+
-+ + + +
+ + + +- --
--
--
-
+ - + + + +
+ + + +- -
-
-
-
-
-
-
+ - + + + +
+ + + +- -
-
-
-
-
-
-
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Tro, Chemistry: A Molecular Approach 35
Ionic Bonding
Model vs. Reality ionic compounds conduct electricity in the liquid state
or when dissolved in water, but not in the solid state
to conduct electricity, a material must have chargedparticles that are able to flow through the material
in the ionic solid, the charged particles are locked inposition and cannot move around to conduct
in the liquid state, or when dissolved in water, the ionshave the ability to move through the structure and
therefore conduct electricity
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Tro, Chemistry: A Molecular Approach 37
Single Covalent Bonds
two atoms share a pair of electrons2 electrons
one atom may have more than one single bond
F
F
F
F
HH O
HH O
F F
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Tro, Chemistry: A Molecular Approach 38
Double Covalent Bond
two atoms sharing two pairs of electrons4 electrons
O O
O
O
O O
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Triple Covalent Bond
two atoms sharing 3 pairs of electrons6 electrons
N
N
N
N
N N
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Covalent Bonding
Predictions from Lewis Theory Lewis theory allows us to predict the formulas of
molecules
Lewis theory predicts that some combinations should bestable, while others should not
because the stable combinations result in octets
Lewis theory predicts in covalent bonding that the
attractions between atoms are directional the shared electrons are most stable between the bonding atoms resulting in moleculesrather than an array
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Tro, Chemistry: A Molecular Approach 41
Covalent Bonding
Model vs. Reality molecular compounds have low melting points and
boiling pointsMP generally < 300C
molecular compounds are found in all 3 states at roomtemperature
melting and boiling involve breaking the attractionsbetween the molecules, but not the bonds betweenthe atoms the covalent bonds are strong
the attractions between the molecules are generally weak
the polarity of the covalent bonds influences the strength ofthe intermolecular attractions
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Tro, Chemistry: A Molecular Approach 42
Intermolecular Attractions vs. Bonding
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Ionic Bonding
Model vs. Reality
some molecular solids are brittle and hard, butmany are soft and waxy
the kind and strength of the intermolecular
attractions varies based on many factors
the covalent bonds are not broken, however, thepolarity of the bonds has influence on these
attractive forces
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Tro, Chemistry: A Molecular Approach 44
Ionic Bonding
Model vs. Reality molecular compounds do not conduct electricity in the
liquid state
molecular acids conduct electricity when dissolved inwater, but not in the solid state
in molecular solids, there are no charged particlesaround to allow the material to conduct
when dissolved in water, molecular acids are ionized,and have the ability to move through the structure and
therefore conduct electricity
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Tro, Chemistry: A Molecular Approach 45
Bond Polarity covalent bonding between unlike atoms results in
unequal sharing of the electronsone atom pulls the electrons in the bond closer to its side
one end of the bond has larger electron density than the
other the result is a polar covalent bondbond polarity
the end with the larger electron density gets a partial
negative charge
the end that is electron deficient gets a partial positivecharge
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Tro, Chemistry: A Molecular Approach 46
HF
H F
d d
FH
EN 2.1 EN 4.0
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Electronegativity
measure of the pull an atom has on bondingelectrons
increases across period (left to right) and
decreases down group (top to bottom)fluorine is the most electronegative element
francium is the least electronegative element
the larger the difference in electronegativity,the more polar the bondnegative end toward more electronegative atom
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Tro, Chemistry: A Molecular Approach 48
Electronegativity Scale
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49
Electronegativity and Bond Polarity If difference in electronegativity between bonded atoms
is 0, the bond is pure covalent equal sharing
If difference in electronegativity between bonded atomsis 0.1 to 0.4, the bond is nonpolar covalent
If difference in electronegativity between bonded atoms0.5 to 1.9, the bond is polar covalent
If difference in electronegativity between bonded atomslarger than or equal to 2.0, the bond is ionic
100%
0 0.4 2.0 4.0
4% 51%Percent Ionic Character
Electronegativity Difference
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Tro, Chemistry: A Molecular Approach 50
Bond Polarity
ENCl= 3.0
3.0 - 3.0 = 0Pure Covalent
ENCl= 3.0
ENH= 2.13.02.1 = 0.9
Polar Covalent
ENCl= 3.0
ENNa= 1.03.00.9 = 2.1
Ionic
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Tro, Chemistry: A Molecular Approach 52
Bond Dipole Moments the dipole moment is a quantitative way of describing the
polarity of a bond a dipole is a material with positively and negatively charged ends
measured
dipole moment, m, is a measure of bond polarity it is directly proportional to the size of the partial charges and
directlyproportional to the distance between them
m= (q)(r)
not Coulombs Law
measured in Debyes, D
the percent ionic characteris the percentage of a bondsmeasured dipole moment to what it would be if full ions
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Dipole Moments
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Watera Polar Molecule
stream of
water
attractedto a
charged
glass rod
stream of
hexane
notattracted
to a
charged
glass rod
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Tro, Chemistry: A Molecular Approach 56
Lewis Structures
of Molecules shows pattern of valence electron distribution in
the molecule
useful for understanding the bonding in manycompounds
allows us to predict shapes of molecules
allows us to predict properties of molecules andhow they will interact together
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Tro, Chemistry: A Molecular Approach 57
Lewis Structures use common bonding patterns
C = 4 bonds & 0 lone pairs, N = 3 bonds & 1 lone pair,O= 2 bonds & 2 lone pairs, H and halogen = 1 bond, Be
= 2 bonds & 0 lone pairs, B = 3 bonds & 0 lone pairs
often Lewis structures with line bonds have the lone
pairs left off their presence is assumed from common bonding patterns
structures which result in bonding patternsdifferent from common have formal charges
B C N O F
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Tro, Chemistry: A Molecular Approach 58
Writing Lewis Structures of Molecules
HNO3
1) Write skeletal structure H always terminal
in oxyacid, H outside attached to Os
make least electronegative atom central N is central
2) Count valence electrons
sum the valence electrons for each
atom add 1 electron for each charge
subtract 1 electron for each + charge
ONOH
O
N = 5
H = 1
O3= 36 = 18
Total = 24 e-
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Writing Lewis Structures of Molecules
HNO33) Attach central atom to the surrounding atoms with
pairs of electrons and subtract from the total
ONOH
O
Electrons
Start 24
Used 8
Left 16
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Tro, Chemistry: A Molecular Approach 60
Writing Lewis Structures of Molecules
HNO34) Complete octets, outside-in H is already complete with 2
1 bond
and re-count electrons
:
::
ONOH
O
N = 5
H = 1
O3= 36 = 18
Total = 24 e-
Electrons
Start 24
Used 8
Left 16
Electrons
Start 16
Used 16
Left 0
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Tro, Chemistry: A Molecular Approach 61
Writing Lewis Structures of Molecules
HNO35) If all octets complete, give extraelectrons to central atom.
elements with dorbitals can havemore than 8 electrons
Period 3 and below
6) If central atom does not haveoctet, bring in electrons fromoutside atoms to share
follow common bonding patternsif possible
:
::
ONOH
|
O
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Practice Lewis Structures
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Tro, Chemistry: A Molecular Approach 63
Practice - Lewis Structures
CO2
SeOF2
NO2-1
H3
PO4
SO3-2
P2H4
:O::C::O:O P
O
O
O
HH
H
F Se
O
F
O S
O
O
O N O
16 e-
26 e-
18 e-
26 e-
32 e-
14 e-H P P H
HH
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Tro, Chemistry: A Molecular Approach 64
Formal Charge during bonding, atoms may wind up with more
or less electrons in order to fulfill octets - thisresults in atoms having a formal charge
FC = valence e- - nonbonding e- - bonding e-
left O FC = 6 - 4 - (4) = 0
S FC = 6 - 2 - (6) = +1
right O FC = 6 - 6 - (2) = -1
sum of all the formal charges in a molecule = 0 in an ion, total equals the charge
O S O
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Tro, Chemistry: A Molecular Approach 65
Writing Lewis Formulas of
Molecules (contd)7) Assign formal charges to the atoms
a) formal charge = valence e-- lone pair e-- bonding e-
b) follow the common bonding patterns
OSO
H
|
HOCCH
|||
OH
0 +1 -1
all 0
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Tro, Chemistry: A Molecular Approach 66
Common Bonding Patterns
B C N O
C
+
N
+
O
+
C
-
N
-
O
-
B
-
F
F+
-F
Practice Assign Formal Charges
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Tro, Chemistry: A Molecular Approach 67
Practice - Assign Formal Charges
CO2
SeOF2
NO2-1
H3
PO4
SO3-2
P2H4
O P
O
O
O
HH
H
F Se
O
F
O S
O
O
O N O
H P P H
HH
Practice Assign Formal Charges
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Tro, Chemistry: A Molecular Approach 68
Practice - Assign Formal Charges
CO2
SeOF2
NO2-1
H3
PO4
SO3-2
P2H4
O P
O
O
O
HH
H
F Se
O
F
O S
O
O
O N O
H P P H
HH
all 0
-1
P = +1
rest 0
S = +1Se = +1
-1
-1all 0
-1
-1-1
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Resonance
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Tro, Chemistry: A Molecular Approach 71
Ozone Layer
Rules of Resonance Structures
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Rules of Resonance Structures
Resonance structures must have the same connectivity only electron positions can change
Resonance structures must have the same number ofelectrons
Second row elements have a maximum of 8 electrons
bonding and nonbonding third row can have expanded octet
Formal charges must total same Better structures have fewer formal charges
Better structures have smaller formal charges Better structures have formal charge on more
electronegative atom
Drawing Resonance Structures
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Tro, Chemistry: A Molecular Approach 73
O N
O
O
Drawing Resonance Structures1. draw first Lewis structure that
maximizes octets
2. assign formal charges
3. move electron pairs from atoms
with (-) formal charge toward
atoms with (+) formal charge
4. if (+) fc atom 2ndrow, only movein electrons if you can move out
electron pairs from multiple
bond
5. if (+) fc atom 3rd
row or below,keep bringing in electron pairs to
reduce the formal charge, even if
get expanded octet.
-1
-1
+1
O N
O
O
-1
-1 +1
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Tro, Chemistry: A Molecular Approach 74
Exceptions to the Octet Rule
expanded octetselements with empty dorbitals can have more
than 8 electrons
odd number electron species e.g., NOwill have 1 unpaired electron
free-radical
very reactive
incomplete octetsB, Al
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Practice -Identify Structures with Better or
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Tro, Chemistry: A Molecular Approach 76
Equal Resonance Forms and Draw Them
CO2
SeOF2
NO2-1
H3PO4
SO3-2
P2H4
O P
O
O
O
HH
H
F Se
O
F
O S
O
O
O N O
H P P H
HH
all 0
-1
P = +1
S = +1Se = +1
-1
-1all 0
-1
-1-1
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Tro, Chemistry: A Molecular Approach 78
Bond Energies
chemical reactions involve breaking bonds in reactantmolecules and making new bond to create the products
the DHreactioncan be calculated by comparing the cost
of breaking old bonds to the profit from making newbonds
the amount of energy it takes to break one mole of abond in a compound is called the bond energy
in the gas state
homolyticallyeach atom gets bonding electrons
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Tro, Chemistry: A Molecular Approach 79
Trends in Bond Energies
the more electrons two atoms share, the strongerthe covalent bond
CC (837 kJ) > C=C (611 kJ) > CC (347 kJ)
CN (891 kJ) > C=N (615 kJ) > CN (305 kJ)
the shorter the covalent bond, the stronger thebond
BrF (237 kJ) > BrCl (218 kJ) > BrBr (193 kJ)
bonds get weaker down the column
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E ti t th E th l f th F ll i R ti
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Tro, Chemistry: A Molecular Approach 83
Estimate the Enthalpy of the Following Reaction
H2(g) + O2(g) H2O2(g)reaction involves breaking 1mol H-H and 1 mol O=O
and making 2 mol H-O and 1 mol O-O
bonds broken (energy cost)
(+436 kJ) + (+498 kJ) = +934 kJ
bonds made (energy release)
2(464 kJ) + (142 kJ) = -1070
DHrxn= (+934 kJ) + (-1070. kJ) = -136 kJ
(Appendix DHf= -136.3 kJ/mol)
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Tro, Chemistry: A Molecular Approach 84
Bond Lengths
the distance between the nuclei ofbonded atoms is called the bondlength
because the actual bond lengthdepends on the other atoms aroundthe bond we often use the average
bond lengthaveraged for similar bonds from
many compounds
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Tro, Chemistry: A Molecular Approach 85
Trends in Bond Lengths
the more electrons two atoms share, the shorter thecovalent bond
CC (120 pm) < C=C (134 pm) < CC (154 pm)
CN (116 pm) < C=N (128 pm) < CN (147 pm) decreases from left to right across periodCC (154 pm)> CN (147 pm)> CO (143 pm)
increases down the columnFF (144 pm)> ClCl (198 pm)> BrBr (228 pm)
in general, as bonds get longer, they also get weaker
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Bond Lengths
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Tro, Chemistry: A Molecular Approach 87
Metallic Bonds
low ionization energy of metals allows them tolose electrons easily the simplest theory of metallic bonding involves
the metals atoms releasing their valence electrons
to be shared by all to atoms/ions in the metalan organization of metal cation islands in a sea of
electrons
electrons delocalized throughout the metal structure
bonding results from attraction of cation for thedelocalized electrons
Metallic Bonding
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Metallic Bonding
Metallic Bonding
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g
Model vs. Reality
metallic solids conduct electricity because the free electrons are mobile, it
allows the electrons to move through the
metallic crystal and conduct electricity as temperature increases, electrical
conductivity decreases
heating causes the metal ions to vibratefaster, making it harder for electrons tomake their way through the crystal
Metallic Bonding
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Tro, Chemistry: A Molecular Approach 90
g
Model vs. Reality
metallic solids conduct heat
the movement of the small, light electronsthrough the solid can transfer kinetic energy
quicker than larger particles
metallic solids reflect light
the mobile electrons on the surface absorbthe outside light and then emit it at the samefrequency
Metallic Bonding
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g
Model vs. Reality
metallic solids are malleable and ductile because the free electrons are mobile, the
direction of the attractive force between the
metal cation and free electrons is adjustable this allows the position of the metal cation
islands to move around in the sea of
electrons without breaking the attractionsand the crystal structure
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