A students work (without solutions manual) ~ 1

1
A students work (without solutions manual) 10
problems/night.
Alanah Fitch Flanner Hall 402 508-3119 afitch_at_luc.
edu Office Hours W F 2-3 pm
Module 10 Covalent Bonding
2
FITCH Rules
G1 Suzuki is Success G2. Slow me down G3.
Scientific Knowledge is Referential G4. Watch out
for Red Herrings G5. Chemists are Lazy C1. Its
all about charge C2. Everybody wants to be like
Mike (grp.18) C3. Size Matters C4. Still Waters
Run Deep C5. Alpha Dogs eat first
General
Chemistry
3
Properties and Measurements
Property Unit Reference State Size
m size of earth Volume cm3 m Weight gram
mass of 1 cm3 water at specified Temp
(and Pressure) Temperature oC, K boiling,
freezing of water (specified Pressure) 1.6605
3873x10-24g amu (mass of 1C-12
atom)/12 quantity mole atomic mass of an
element in grams Pressure atm, mm Hg earths
atmosphere at sea level Energy Thermal BTU 1
lb water 1 oF calorie 1 g water 1
oC Kinetic J 2kg mass moving at 1m/s Energy,
of electrons energy of electron in a
vacuum Electronegativity F
4

• Bonding sharing electrons between repulsive
  nuclei
• Lewis Dot structures help us visualize sharing of
  electrons
• Octets
• Double and triple bonds
• Resonance structures and No Clean Socks
• Formal Charge to help distinguish between
  alternatives
• Violations of the Octet Rule
• 2 electrons
• gt8 electrons
• Using electrons to predict the SHAPE of the
  molecules
• VESPR
• Effect of unpaired electrons on the central atom
  on molecular shape
• Effect of Multiple bonds
• How to deal with no central atom
• Bond polarity
• Effect of electronegativity difference between
  atoms in bond
• Effect of molecular shape
• How to symbolize bond polarity
• Discrepancies between Electron Orbital Diagrams
  and VESPR

5
Covalent bonding
Patterns in abundance suggest a. periodicity b.
preferred electronic configuration of
elements Leading to the Rule Everybody wants
to be Like Mike a. Ions Groups 16 and 17 gain
electrons Groups 1 and 2 lose b. Other atoms
share electrons to have eight electrons
COVALENT BONDING
6
Covalent Bonding getting to a noble gas
electron configuration by sharing electrons

• Bring two elements close together
• When very close the positive nuclei repel each
  other

Repulsion of two hydrogen atoms with their
Proton core


7
Repulsion of two hydrogen atoms with their proton
core
Repulsion is high close where Protons see each
other
Atoms which are far apart Do not even see each
other There is no energy, repulsive Or attractive
between the two
Repulsion is low where Electrons shield nucleus,
and where Electrons can be stabilized by
both Positive charges
Repulsive energy
Electrons are the jelly and peanut butter between
the slices of bread (protons)
Attractive energy
8
A students work (without solutions manual) 10
problems/night.
Alanah Fitch Flanner Hall 402 508-3119 afitch_at_luc.
edu Office Hours W F 2-3 pm
9

• Bonding sharing electrons between repulsive
  nuclei
• Lewis Dot structures help us visualize sharing of
  electrons
• Octets
• Double and triple bonds
• Resonance structures and No Clean Socks
• Formal Charge to help distinguish between
  alternatives
• Violations of the Octet Rule
• 2 electrons
• gt8 electrons
• Using electrons to predict the SHAPE of the
  molecules
• VESPR
• Effect of unpaired electrons on the central atom
  on molecular shape
• Effect of Multiple bonds
• How to deal with no central atom
• Bond polarity
• Effect of electronegativity difference between
  atoms in bond
• Effect of molecular shape
• How to symbolize bond polarity
• Discrepancies between Electron Orbital Diagrams
  and VESPR

10
Lewis dot structure (electron dot Structure or
diagram) are diagrams that Show the bonding
between atoms of A molecule based on shared
valence shell (outer shell) electrons and shows
the Presence of any lone pair of electrons That
may exist in the covalently bonded Molecule.
Gilbert Newton Lewis 1875-1946 Caltech Physical
Chemist
Covalent
Valence outermost shell electrons of an atom
shared
Latin valere to be strong
11
When the two hydrogen atoms are together, the
electron configuration Looks like?
He
When a hydrogen atom and a fluorine atom share
electrons, the Electron configuration on
fluorine looks like?
The inner shell electrons do not Show
in this diagram
12
When the two hydrogen atoms are together, the
electron configuration Looks like?
He
When a hydrogen atom and a fluorine atom share
electrons, the Electron configuration on
fluorine looks like?
Only the outer-most or valence shell electrons
Show in this Lewis Dot Structure
How many valence electrons? last number in
group
13
When the two hydrogen atoms are together, the
electron configuration Looks like?
He
When a hydrogen atom and a fluorine atom share
electrons, the Electron configuration on
fluorine looks like?
The shared pair of Electrons covalent bond
The unshared pairs of electrons are regions of
high Charge density
14
When a hydrogen atom and an oxygen atom share
valence electrons plus an Extra electron, the
electron configuration on hydrogen and oxygen
look like?
Valence electrons on oxygen?
Valence electrons on hydrogen?
Invoking Rule Chemists are Lazy the diagram
above is too tedious to write out all the
time make shared electrons (bond) a line
Lewis dot structure for hydroxide
The single electron pair shaired between the two
bonded atoms Is called a single bond It is drawn
as a line.
15
When two hydrogen atoms and an oxygen atom share
valence electrons, the electron configuration on
hydrogen and oxygen look like?
Two shared electron pairs
Two shared electron pairs Two single bonds
16
When two hydrogen atoms and an oxygen atom share
valence electrons, the electron configuration on
hydrogen and oxygen look like?
When three hydrogen atoms and a nitrogen atom
share valence electrons, the electron
configuration on hydrogen and nitrogen look like?
17
When two hydrogen atoms and an oxygen atom share
valence electrons, the electron configuration on
hydrogen and oxygen look like?
When three hydrogen atoms and a nitrogen atom
share valence electrons, the electron
configuration on hydrogen and nitrogen look like?
Valence shell of nitrogen?
Three pairs of shared electrons three single
bonds
18
When four hydrogen atoms and two carbon atoms
share valence electrons, the electron
configuration on hydrogen and carbon look like?
Valence shell of carbon?
Two electron pairs shared is a Double bond
19
When two hydrogen atoms and two carbon atoms
share valence electrons, the electron
configuration on hydrogen and carbon look like?
Three electron pairs shared is a Triple bond
20
Rules for Writing Lewis Dot Structures

• Count the number of valence electrons (last
  number of group) of all atoms
• a. For an anion add the appropriate extra number
  of electrons
• b. For a cation subtract the appropriate extra
  number of electrons
• Draw a molecular skeleton, joining by single
  bonds to the central atom.
• a. The central is usually the atom written first
  in the formula (N in NH4, S in SO2, and C in
  CCl4).
• b. The terminal atoms are usually H, O.
• c. Halogens are always terminal atoms.
• Determine the number of valence electrons still
  available for distribution after subtracting two
  electrons for each single bond.
• Determine the number of electrons required to
  complete the octet
• a. H gets only two electrons
• b. Other exceptions to be noted below
• 5. Fill in the region required for the octet.
• Make up deficit of electrons by creating double
  bonds
• a. C, N, O, S

H can only have one bond because it can share
only one Electron. Poor H.
Halogens have lots of electrons but really do not
like to share. Greedy halogens All they want is
one more to make up the Mike configuration
21

• Draw Lewis structures of
• Hypochlorite ion
• Methyl alcohol
• N2
• SO2

Valence shell electrons?
O 6 Cl 7 Negative charge 1 Total
electrons 14 -1Single bond -2
12 -2(6 electrons for
O,Cl) 12 remaining 0
Hypochlorite? Hypo smallest number of oxygens
OCl-
Skeleton
22

• Draw Lewis structures of
• Hypochlorite ion
• Methyl alcohol, CH3OH
• N2
• SO2

Skeleton
Carbon is first in formula Hydrogen is always
terminal
Valence shell electrons?
O 6 C 4 4(H) 4 Negative charge
0 Total electrons 14 -5single bonds -10
remaining 4 -octet for oxygen -4 remaining 0
Octets
Carbon has its octet Hydrogen has its duet Oxygen
requires 4 more electrons
23

• Draw Lewis structures of
• Hypochlorite ion
• Methyl alcohol, CH3OH
• N2
• SO2

Skeleton
Octets
Each nitrogen requires 6 more
Valence shell electrons?
2N 10 Negative charge 0 Total
electrons 10 -1single bond -2 Remaining 8 Octet
completion -12 Difference -4
2N 10 Negative charge 0 Total
electrons 10 -3 single bonds -6 Remaining 4
We are short 4 electrons for the octet, The only
way to get extra ones is to Share four more
electrons triple Bond.
Place the remaining 4 electrons equally On the
two equal nitrogens
24
Skeleton, First atom in formula is central

• Draw Lewis structures of
• Hypochlorite ion
• Methyl alcohol, CH3OH
• N2
• SO2

Octets
We are short 2 electrons for the octet, The only
way to get extra ones is to Share two more
electrons double bond.
Valence shell electrons?
2O 12 1S 6 Negative charge 0 Total
electrons 18 -2(single bonds) -4 Remaining
electrons 14 Octet for S -4 2(Octet for each
O) -12 Deficit? -2 2O 12 1S 6 Negative
charge 0 Total electrons 18 -3(single
bonds) -6 12
Place the remaining 12 electrons to fill octets
25
We got this Lewis dot structure
No reason not to write instead
Which would lead to
Is there any reason for us to Presume one of
these is correct And not the other?
No
Grammar double-headed arrow is used to separate
resonance structures
26

• Bonding sharing electrons between repulsive
  nuclei
• Lewis Dot structures help us visualize sharing of
  electrons
• Octets
• Double and triple bonds
• Resonance structures and No Clean Socks
• Formal Charge to help distinguish between
  alternatives
• Violations of the Octet Rule
• 2 electrons
• gt8 electrons
• Using electrons to predict the SHAPE of the
  molecules
• VESPR
• Effect of unpaired electrons on the central atom
  on molecular shape
• Effect of Multiple bonds
• How to deal with no central atom
• Bond polarity
• Effect of electronegativity difference between
  atoms in bond
• Effect of molecular shape
• How to symbolize bond polarity
• Discrepancies between Electron Orbital Diagrams
  and VESPR

27
Remember our Low Charge Density Spectator
Polyatomic Anions?
No Clean Socks
NO3-

• N 5
• 3(O) 18
• Charge 1
• Total 24
• -single bonds -6
• Remaining 18
• Octets (6x3 O 2 for N) -20
• Deficit of 1 electron pair -2
• N 5
• 3(O) 18
• Charge 1
• Total 24
• Bonds -8
• 16

Charge is distributed over All three of the
resonance Forms one big fat marshmallow
28

• Resonance
• The real molecule is none of the three nitrates
  we drew but something intermediate to the three.
• Resonance can be assumed or predicted when
  there are equally plausible Lewis dot structures.
• Resonance forms differ only in the distribution
  of electrons and not in the arrangement of atoms.

29
Write three resonance forms for SO3
Valence electrons 4(6) 24 Sulfur central
atom Three single bonds to the sulfur -3(2)
-6 Remaining electrons 18 2 electrons to
complete S octet -2 3(6) electrons to complete O
octets 18 -18 Deficit of two electrons double
bond -2 Valence electrons 4(6) 24 Sulfur
central atom Four single bonds to the
sulfur -3(2) -8 Remaining electrons 16
30

• Bonding sharing electrons between repulsive
  nuclei
• Lewis Dot structures help us visualize sharing of
  electrons
• Octets
• Double and triple bonds
• Resonance structures and No Clean Socks
• Formal Charge to help distinguish between
  alternatives
• Violations of the Octet Rule
• 2 electrons
• gt8 electrons
• Using electrons to predict the SHAPE of the
  molecules
• VESPR
• Effect of unpaired electrons on the central atom
  on molecular shape
• Effect of Multiple bonds
• How to deal with no central atom
• Bond polarity
• Effect of electronegativity difference between
  atoms in bond
• Effect of molecular shape
• How to symbolize bond polarity
• Discrepancies between Electron Orbital Diagrams
  and VESPR

31
Formal Charge helps determine the correct Lewis
Dot Structure
Xnumber of valence e- in the free atom (last
number of group) Y number of unshared e- owned
by the atom in the Lewis structure Z number of
bonding e- shared by the atom in the Lewis
structure

• The correct Lewis dot structure is generally the
  one in which
• The formal charges are as close to zero as
  possible
• Negative charge is located on the more
  electronegative atom

32
Xnumber of valence e- in the free atom (last
number of group) Y number of unshared e- owned
by the atom in the Lewis structure Z number of
bonding e- shared by the atom in the Lewis
structure
Which is correct?
33

• Bonding sharing electrons between repulsive
  nuclei
• Lewis Dot structures help us visualize sharing of
  electrons
• Octets
• Double and triple bonds
• Resonance structures and No Clean Socks
• Formal Charge to help distinguish between
  alternatives
• Violations of the Octet Rule
• 2 electrons
• gt8 electrons
• Using electrons to predict the SHAPE of the
  molecules
• VESPR
• Effect of unpaired electrons on the central atom
  on molecular shape
• Effect of Multiple bonds
• How to deal with no central atom
• Bond polarity
• Effect of electronegativity difference between
  atoms in bond
• Effect of molecular shape
• How to symbolize bond polarity
• Discrepancies between Electron Orbital Diagrams
  and VESPR

34
The Octet Rule is a form of Rule C2- Everybody
wants to be like a Noble gas
In same fashion not everybody can share
enough Electrons to make up a perfect octet
These guys will have 1, 2, and 3
bonds only
35
The Octet Rule is a form of Rule C2- Everybody
wants to be like a Noble gas
In same fashion not everybody can share
enough Electrons to make up a perfect octet
This guy may end up holding the bag Having an
unpaired electron
Because he is Not really Strong enough To always
Get the lions Share of the Electrons in A
covalent bond, Particularly With oxygen
The unpaired electron means The compound is
paramagnetic
The presence of these unpaired electrons on these
gases Gives rise to the many atmospheric
reactions involved In ozone destruction and
formation of smog.
Para paramour love similar orientation
Dia diatribe against opposite
orientation
36
A singlet electron is also called a free radical
Aging
Hydroxy radical
hydroxide
Cellular membrane damage
http//www.thedoctorslounge.net/oncology/articles/
oxidcar/oxidcar2.htm
37
After hydroxyl radical cleavage and denaturing
gel electrophoresis, the gel patterns differ. The
unfolded RNA molecule is cleaved uniformly,
giving rise to a homogeneous ladder of bands on
the gel (left, bottom). The gel pattern for the
folded RNA (right, bottom), in contrast, shows
several region where strand cleavage is
inhibited, corresponding to the sites of low
solvent accessibility in the folded structure
(right, top).
TD Tullius, JA Greenbaum, Curr Opin Chem Biol
2005, 9127134 (Figure 1)
Commentary from grove.ufl.edu/dmorgan/Articles/DE
R/Journal20Club.ppt
38
The Octet Rule is a form of Rule C2- Everybody
wants to be like a Noble gas
Some guys can take on more electrons because
they Make use of their d orbitals
these guys Have d orbitals That allow them To
have more Than 8 electrons
3p
3d
4s
39
Draw the Lewis structure of XeF4
84(7) 36 electrons 4bonds 8
electrons Remainder 28 electrons Octets 4(6)
for F 24 Remainder to Xe 4
40
Draw the Lewis structure of XeF2
82(7) 22 electrons 2bonds 4
electrons Remainder 18 electrons Octets 2(6)
for F 12 Remainder to Xe 6
41
A students work (without solutions manual) 10
problems/night.
Alanah Fitch Flanner Hall 402 508-3119 afitch_at_luc.
edu Office Hours W F 2-3 pm
42

• Bonding sharing electrons between repulsive
  nuclei
• Lewis Dot structures help us visualize sharing of
  electrons
• Octets
• Double and triple bonds
• Resonance structures and No Clean Socks
• Formal Charge to help distinguish between
  alternatives
• Violations of the Octet Rule
• 2 electrons
• gt8 electrons
• Using electrons to predict the SHAPE of the
  molecules
• VESPR
• Effect of unpaired electrons on the central atom
  on molecular shape
• Effect of Multiple bonds
• How to deal with no central atom
• Bond polarity
• Effect of electronegativity difference between
  atoms in bond
• Effect of molecular shape
• How to symbolize bond polarity
• Discrepancies between Electron Orbital Diagrams
  and VESPR

43
Can now predict SHAPE of molecule determines
how two molecules orient themselves for
reaction together. Can they dock? And actually
do work together in three dimensional space?
44
Valence Shell Electron Pair Repulsion
Rule C1 Its all about charge
Eel
d
Valence electron pairs surrounding an atom repel
one another. Consequently, the orbitals
containing those electron pairs are oriented to
be as far apart as possible
45
Geometries of AX2-AX6 molecules
A
X
X
Repulsion of valence shell electrons in Bonds and
on F push F apart to a 180o orientation
46
Geometries of AX2-AX6 molecules
What orientation would put electrons as far apart
as possible?
120o degrees apart in a circle
47

• Draw Lewis structures of
• CH4

Valence shell electrons?
C 4 4(H) 4 Negative charge 0 Total
electrons 8 -4single bonds -8 remaining 0
Skeleton
Carbon is first in formula Hydrogen is always
terminal
Octets
Carbon has its octet Hydrogen has its duet
48
How can four bonds be organized in 3-D space
to be farthest apart?
X
X
X
A
X
49
A pyramid is a space figure with a square base
and 4 triangle-shaped sides. (5 faces)
1
A tetrahedron is a space figure and 4 triangle
shaped faces.
Dictionary a four-sided solid a Triangular
pyramid
50
A pyramid is a space figure with a square base
and 4 triangle-shaped sides. (5 faces)
Dictionary Square base and sloping Sides
rising to an apex
1
A tetrahedron is a space figure and 4 triangle
shaped faces.
Dictionary a four-sided solid a Triangular
pyramid
51
A pyramid is a space figure with a square base
and 4 triangle-shaped sides. (5 faces)
Dictionary 1 Square base and sloping Sides
rising to an apex
Dictionary 2 A solid figure with a polygon
base. The surface, or lateral faces, are
triangles having a common vertex. In a regular
pyramid the base is a regular polygon and the
lateral faces are congruent triangles
1
A tetrahedron is a space figure and 4 triangle
shaped faces.
Dictionary a four-sided solid a Triangular
pyramid
SIGNIFICANT AMBIGUITY In nomenclature!!!!
52
Why tetrahedron and not this orientation? (Square
planar)
Calculate the repulsion experience By atom X1
with charge -1
X1 ,1-
90 o
180 o
X2,1-
X4,1-
A
Assume Bond distance1
X3,1-
Since our example has all Q the same
53
Why tetrahedron and not this orientation?
X1,1-
90 o
d14
d12
1
X2,1-
X4,1-
A
d13
X3,1-
Calculation suggests that the electrostatic
charge repulsion Energy is proportional to 1.914
for a square planar orientation Of four
identically charged atoms
54
Square planar orientation 1.914 Compare to
tetrahedron
1
d14
A
4
2
3
This means atom 1 experiences less
charge Repulsion from 2, 3, and 4 when tetrahedral
55
Geometries of AX2-AX6 molecules
56
Geometries of AX2-AX6 molecules
Triangular pyramid
Triangular bipyramid
ACentral atom X atoms
How can five bonds be arranged in space to be as
far apart as possible?
57
Geometries of AX2-AX6 molecules
SF6
octahedron
How can these six guys best position
themselves away from each other?
58
(No Transcript)
59
Some of the molecules we constructed using Lewis
Dot structures had UNSHARED PAIRS of electrons
on the CENTRAL ATOM What effect will this have
on the geometry?.
AX2E
Unshared electron pairs orient themselves pretty
much the same as single bonds.
The observed molecular geometry (invisible
electrons) is very different
60
AX2E
This geometry, with respect to electron pairs and
bonds, is triangular planar (three guys trying to
get out of each others way)
But one of the terminal atoms is missing so the
molecular geometry differs from triangular planar
lt120
Actual degrees observed is slightly less than
120o because unshared electron pair expands
Molecular Geometry is bent
61
AX3
Molecular Geometry
Triangular planar
Triangular planar
AX2E
120 o
Bent
62
AX3E
This geometry, with respect to electron pairs and
bonds, is tetrahedral (four guys trying to get
out of each others way)
But one of the terminal atoms is missing so the
molecular geometry differs from tetrahedral
Triangular Pyramid
Explains why amines like ammonia can steal a
proton From water high charge density from the
lone pair
63
Effect of lone pairs on substituents (non-central
atoms)
F
F
102.3o
F
107.2o
64
Effect of F is NOT by geometry of its lone
pairs BUT By its electronegativity which pulls
electrons along the bond, lowers Density of
electrons in the bondings area Allows N lone pair
to expand Compressing the angle between F atoms
F
F
107.2o
F
102.3o
65
What happens when we have Two Unbonded electron
pairs on the Central atom, A?
AX2E2
This geometry, with respect to electron pairs and
bonds, is tetrahedral (four guys trying to get
out of each others way)
But two of the terminal atoms are missing so
the molecular geometry differs from tetrahedral
This shape is bent
66
Both are bent, but the angle is
different. Depends upon the number of valence
shell electron pairs
AX2E
AX2E2
67
AX4
Molecular Geometry
Tetrahedron
Triangular pyramid
AX3E
Tetrahedron
lt109.5o
Tetrahedron
lt109.5o
Bent
AX2E2
68
5 ELECTRON PAIRS
Molecular Orientation
Triangular bipyramid
Triangular pyramid
Triangular bipyramid
Triangular bipyramid
180o
Linear
AX2E3
XeF2
Triangular bipyramid
AX3E2
90o 180o
ClF3
T-shape
Why put the E at equator?
69
Comparing where the non-bonded electron pair
will go Variations Axial versus Equatorial
orientation
90o
S
E
S
S
120o
E
S
E
S
S
E
1
2
E non-bonding Electron pair S Shared (bonded)
electron pair
Electrostatic repulsion is sum of all near
neighbor repulsions
70
If we put the E at the axial orientation they
minimize E-E repulsion increase E-S
repulsion If we put E at the equatorial
orientation E-E repulsion exists, but we
decrease the E-S repulsion
E
E
Minimizes impact Of E on S
71
5 ELECTRON PAIRS
Molecular Orientation
Triangular pyramid
Triangular bipyramid
Triangular bipyramid
180o
Linear
AX2E3
XeF2
Triangular bipyramid
AX3E2
90o 180o
ClF3
T-shape
72
Molecular Orientation
SF6
octahedron
octahedron
Square pyramidal
octahedron
AX4E2
90o 180o
Square planar
XeF2
73
Why electron configuration is important
controls shape of molecule dictates 3D
interaction of molecules
Anticancer Drug
Square planar lets it slide into the DNA grove
74
MULTIPLE Bonds
Has no effect on geometry Multiple bond acts as a
single bond
Compare BF3 and SO3
Triangular Planar
75
Compare Molecular Geometries for BeF2 and CO2 1.
We already did BeF2
76
Compare Molecular Geometries for BeF2 and CO2 1.
We already did BeF2
Skeleton
Carbon is first in formula central atom
Valence shell electrons for CO2?
C 4 2(O) 4 Negative charge 0 Total
electrons 16 -2single bonds -4
remaining 12 e required for octets -16 deficit
multiple bonds -4 C 4 2(O) 4 Negative
charge 0 Total electrons 16 -4bonds -8 Remain
ing 8
Octet for C 0 Octet for each O 4
77
Compare Molecular Geometries for BeF2 and CO2
Both are linear
78
Figure out geometry with NO CENTRAL ATOM
Consider each carbon separately
AX3
Geometry around the carbon Triangular Planar
79
Figure out geometry with NO CENTRAL ATOM
Consider each carbon separately
AX2
Geometry around the carbon Linear
80
4 3 4
Number of Electron Domains Electron-domain
geometry Predicted Bond Angles
Tetrahedral Trigonal Tetrahedral Planar
109.5o 120o 109.5o
81
A students work (without solutions manual) 10
problems/night.
Alanah Fitch Flanner Hall 402 508-3119 afitch_at_luc.
edu Office Hours W F 2-3 pm
82

• Bonding sharing electrons between repulsive
  nuclei
• Lewis Dot structures help us visualize sharing of
  electrons
• Octets
• Double and triple bonds
• Resonance structures and No Clean Socks
• Formal Charge to help distinguish between
  alternatives
• Violations of the Octet Rule
• 2 electrons
• gt8 electrons
• Using electrons to predict the SHAPE of the
  molecules
• VESPR
• Effect of unpaired electrons on the central atom
  on molecular shape
• Effect of Multiple bonds
• How to deal with no central atom
• Bond polarity
• Effect of electronegativity difference between
  atoms in bond
• Effect of molecular shape
• How to symbolize bond polarity
• Discrepancies between Electron Orbital Diagrams
  and VESPR

83
Bond Polarity

• Polarity distribution of electrons in the bond
• Depends upon the difference in electronegativity
  of bonded atoms
• If two atoms in the bond are identical nonpolar
• Otherwise all bonds are polar

84
Decreasing size
Electronegativity is a measure of Positive
Nuclear charge density experienced by Electron on
another atom , scaled to a maxium of 4
HH HC HF
?E.N. 2.2-2.20
nonpolar
?E.N. 2.5-2.2 0.3
slightly polar
?E.N. 4-2.21.8
strongly polar
85
Molecular Polarity
Depends on 1. bond polarity 2. molecular
shape a. diatomic molecules are
linear molecule polar if atoms
differ b. Polyatomic molecules can have
polar bonds and still be non-polar

• HCl ClCl
• polar nonpolar

Polar molecules line up in an electric field
86
Arrow indicates the direction in which
electrons are biased - the negative pole
CCl4

• F ? Be ? F

Bonds are polar ?E.N. 4-1.62.4
Bonds are polar ?E.N. 3.5-2.21.3
Vectors cancel each other
Non-polar molecule
Net charge direction
Polar molecule
Bonds are polar ?E.N. 2.5-3.20.7
No net charge direction
Non polar molecule
87
Very polar bonds (F4 Be1.6)
Non-polar
polar
Changing Central atom so That a lone Electron
pair Bends the molecule Means Vectors Dont cancel
Changing One atom Means Vectors Dont cancel
polar
Non polar
Very polar bonds (Cl 3.2 C2.5)
88
A students work (without solutions manual) 10
problems/night.
Alanah Fitch Flanner Hall 402 508-3119 afitch_at_luc.
edu Office Hours W F 2-3 pm
89

• Bonding sharing electrons between repulsive
  nuclei
• Lewis Dot structures help us visualize sharing of
  electrons
• Octets
• Double and triple bonds
• Resonance structures and No Clean Socks
• Formal Charge to help distinguish between
  alternatives
• Violations of the Octet Rule
• 2 electrons
• gt8 electrons
• Using electrons to predict the SHAPE of the
  molecules
• VESPR
• Effect of unpaired electrons on the central atom
  on molecular shape
• Effect of Multiple bonds
• How to deal with no central atom
• Bond polarity
• Effect of electronegativity difference between
  atoms in bond
• Effect of molecular shape
• How to symbolize bond polarity
• Discrepancies between Electron Orbital Diagrams
  and VESPR

90
The fly in the ointment
Repulsion of valence shell electrons pushes
F apart to a 180o orientation
VSEPR AX2 Linear
VSEPR model suggests that once Be bonds to F the
orbitals are equivalent and therefore are
equidistant from each other.
But the electron orbital diagram suggests
otherwise that Be has paired electrons and would
not make bonds at all.
91

• Be has no unpaired electrons available for bonding

Orbital diagram of isolated atoms F and Be

• Be promotes 1 2s electron to a 2p orbital
• sp hybridization

Orbital diagram of isolated F and hybridized Be
atoms
4. The new sp electrons engage in bonding with
the unpaired electrons on F
sp
Shared electrons
Orbital diagram of F and Be in BeF2
92
Formation of Hybrid Atomic Orbitals
S p orbitals 2 sp hybridized orbitals

The number of hybridized orbitals formed
number of atomic orbitals mixed
Energies of hybridized orbitals intermediate to
the atomic orbitals mixed
93
What does the bond made from the atomic sp
and p atomic orbitals look like?
sp

94
VSEPR AX3 Triangular Planar
Orbital diagram of isolated atoms F and B

• 1. Boron needs to have three of its electrons
  shared with the three F electrons to create the
  three single bonds.
• B mixes 2 s2 and 1 2p electrons using 1 s and
  2 p orbitals
• 3 sp2 atomic orbitals with 1 e each
• formed
• 4. Electrons in these orbitals are
• shared with unpaired electrons on
• F to create single bonds (blue)

sp2
95
What does an sp2 orbital look like?
96
VSEPR AX4 Tetrahedral

• C needs four energetically equivalent bonds
• C mixes 1 2s and 3 2p atomic orbitals
• 4 sp3 atomic orbitals formed
• sp3 orbitals used to create bonds

Orbital diagram of isolated atoms H and C
sp3
97
sp3 orbital on C s orbital on H Form a
sigma bond
98
(No Transcript)
99
So far we have considered
sp
VSEPR AX2 Linear
2 orbitals
VSEPR AX3 Triangular Planar
sp2
3 orbitals
VSEPR AX4 Tetrahedral
sp3
4 orbitals
What about the guys with expanded octets?
100
VSEPR AX5 Triangular bipyramid
these guys Have d orbitals That allow them To
have more Than 8 electrons
3p
3d
4s
101
VSEPR AX5 triangular bipyramid
sp3d
102
VSEPR
AX2 AX3 AX4 AX5 AX6
Nothing new here same as we got with VSEPR
Note to myself from 2006 F does not hybridize
has one unpaired electron Forming one bond
103
Hybridize to Create Equivalent Orbitals on One
atom for Bonding with another atom
Hybridized Orbitals From two diff atoms combine
to create Bonding orbitals
Atomic Orbitals
0kJ
180o
180o
-kJ
104
Double and Triple Bonds
Whenever we have a single bond we can assume
that it has the sigma shape, resulting from
hybridization between atomic orbitals
Sigma bond Single bond
For double and triple bonds, we do not need to
create more equivalent bonds which can be moved
as far apart as predicted by Valence Shell
Electron Pair Repulsion.
We need to simply create additional bonds within
the shape predicted by VSEPR
Pi bond Double bond around single bond
105
What does ethylene, C2H4 look Like?
AX3
Geometry around the carbon Triangular Planar
106
(No Transcript)
107
What does acetylene, C2H2, look like?
AX2
Geometry around the carbon Linear
108
Example problem What is the hybridization of
nitrogen in a) NO3-, b) NH2Cl, c)
N2, d) and N2O?

• Make the Lewis dot structure
• Count sigma bonds on central atom
• Count the unbonded electron pairs on central atom
• Sum the 2 (n)
• Number of hybridized orbitals n

109
RESONANCE
110
Benzene, C6H6, is a very common compound
Usually dont show Hydrogens or Carbons
P orbitals
Sigma bonds
Benzene resonance
Pi (double) bonds
Charge delocalization
111
BIG KEY POINT!!!!!!
Delocalization/Resonance Structures
Nitrate no clean socks
Nitrate is a is not charge dense Poor Nitrate
1 charge
Low Charge density
Large radius
112

• Bonding sharing electrons between repulsive
  nuclei
• Lewis Dot structures help us visualize sharing of
  electrons
• Octets
• Double and triple bonds
• Resonance structures and No Clean Socks
• Formal Charge to help distinguish between
  alternatives
• Violations of the Octet Rule
• 2 electrons
• gt8 electrons
• Using electrons to predict the SHAPE of the
  molecules
• VESPR
• Effect of unpaired electrons on the central atom
  on molecular shape
• Effect of Multiple bonds
• How to deal with no central atom
• Bond polarity
• Effect of electronegativity difference between
  atoms in bond
• Effect of molecular shape
• How to symbolize bond polarity
• Discrepancies between Electron Orbital Diagrams
  and VESPR

113
A students work (without solutions manual) 10
problems/night.
Alanah Fitch Flanner Hall 402 508-3119 afitch_at_luc.
edu Office Hours W F 2-3 pm