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Transcript of 7/15/2015 One Point Quiz One quiz per table, list everyone’s name Agree on an answer You have...
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04/19/23
One Point Quiz
One quiz per table, list everyone’s name Agree on an answer You have two minutes
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Exam 3 Results
0
2
4
6
8
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12
50-59%
60-69%
70-79%
80-89%
90-100%
Exam 1 Exam 2 Exam 3
Nomenclature
Average = 95/110
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Hardest Questions?
Why is the first ionization energy of nitrogen greater than carbon, oxygen or phosphorous?
Li Be B C N O F Ne124 215 191 260 335 314 402 497 kcal
Primary reason:Change of nuclear charge.
Secondary reason:Electronic configuration effects.
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Hardest Questions?
Why is the melting point of magnesium oxide 2000 degrees greater than potassium bromide? (two factors)
Ionic bonding lattice energy q1 x q2 / r
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Orbital HybridizationEdward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
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04/19/23
Bonding Theories
Ionic Model Skeleton Diagrams Lewis Dot Diagrams Molecular Orbital Theory Orbital Hybridization
• Extends molecular orbitals concepts to atoms
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04/19/23
Beryllium Hydride
Be: 1s2 2s2 2p0
H: 1s1Be••H •• H
Impossible to fulfill the octet ofberyllium because there are onlyfour valence electrons available.
Draw a Lewis Dot structure for BeH2
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04/19/23
Beryllium Hydride
Be
BeH
2zb
2sb
HUsing molecular orbitalbonding theory thep-orbitals of berylliummust be used.
This would indicatethat each hydrogen isbound to beryllium bya different type of bond.
Experimentally, the two Be-H
bonds are identicalsame length,
same bond energy (strength)
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04/19/23
Beryllium Hydride
BeH
2zb
2sb
Be H
It is unlikely that2s
b and 2zb
would be exactlyequivalent.
And, there’s another problem ...
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04/19/23
2sb)3
2zb)1
Beryllium Hydride
Open orbital contains no electronsLined orbital contains one electronFilled in orbital contains two electrons
What’s a solution?
HBe
H Be
Be H 2zb)2
H Be 2sb)2
One overlap hasone electron
One overlap hasthree electrons
hybridization
Each overlap hastwo electrons
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04/19/23
Hybridization
The 2s and the 2p orbitals of beryllium have become equivalent to each other by merging or blending or "hybridizing".
These two new orbitals are called sp hybrid atomic orbitals (hao)• Arises from one s orbital and one p orbital.
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04/19/23
Beryllium sp Hybridization
Be
Be
Be Beand
Two orbitalseach can hold two electrons
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04/19/23
sp Hybridization
Be
px, py
sp
ener
gy
2s
2p
ao hao
Maximum angle thattwo orbitals can be
apart is 180°.
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04/19/23
sp Orbital Hybridization
Be
Be
Be
Be
BeThe shape is determined
by the linear combinationsof atomic orbitals
2s + 2pzand 2s - 2pz
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04/19/23
z
y
x
sp Hybridized BerylliumValence Orbitals
Open orbital contains no electronsLined orbital contains one electronFilled in orbital contains two electrons
The other p-orbitalsof beryllium (px, py)remain unchanged
HH Be z
y
x
H two sigmabonds
BeH H
Why is it a linear molecule?
H
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04/19/23
Ethene
C••••H
••
H••
CH
• •
H • •
Also called ethylene Polymerizes to form polyethylene Each carbon forms three sp2 hybrid orbitals.
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04/19/23
One Point Quiz
One quiz per table, list everyone’s name Agree on an answer You have two minutes
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04/19/23
C+
sp2 Orbital Hybridization
C
2s
C+ =
2pz2px sp2
The 2s, 2px and 2pz atomic orbitalsof each carbon are used.
The angle between the orbitals is 120°.
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04/19/23
ener
gy
2s
2p
ao
sp2 Hybridization
hao
sp2
The unhybridized py orbital isperpendicular to the sp2 orbitals.
2py
This hybrid setcan hold six electrons.
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04/19/23
Ethene
Top down view(xz plane)
Edge on view
y
To allow for overlap of the unhybridized py orbitals, the bonding in this molecule requires that ethene is planar. All six atoms lie in the same plane.
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04/19/23
Ethene
CCHH
HH
carbon-carbon sigma bonddue to sp2-sp2 overlap
carbon-carbon pi bonddue to 2py- 2py overlap
carbon-hydrogensigma bonds
due to sp2-s overlap
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04/19/23
Predicting Hybridization
The number of hybrid orbitals an atom formsequals the number of unique directions
that the electron pairs point,as determined by the Lewis Dot structure.
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04/19/23
Methane
C
• •• •
••••H H
H
H
The 2s, 2px , 2py and 2pz atomic orbitalsof carbon are used.
What would be the name of a hybrid orbitalmade from these orbitals?
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04/19/23
sp3 Orbital Hybridization
+
2s
+
2pz2px
+ zy
x
2py
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04/19/23
sp3 Orbital Hybridization
four sp3 orbitals
The angle between the orbitals is 109.5°.
Why isn’t the angle 90°?
tetrahedral shape
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04/19/23
sp3 Hybridization
sp3
ener
gy
2s
2p
carbonao
hao
All four hybridatomic orbitalshave the sameenergy.
These four orbitals areenergetically degenerate.
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04/19/23
Methane
HCH
H
Hcarbon-hydrogen
sigma bondsdue to sp3-s overlap
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04/19/23
Ammonia
••N
• •• •
••H H
H
The 2s, 2px , 2py and 2pz atomic orbitals of nitrogenare used
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04/19/23
sp3 Hybridization
sp3
nitrogenao
hao
ener
gy
2s
2p
By hybridizing itsatomic orbitalsnitrogen gains
more stable(lower energy)
orbitals for bonding.
Which of the electrons in thesehybrid atomic orbitals are available for bonding?
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04/19/23
Ammonia
HNH
H
• •
a completely filled inorbital containstwo electrons
nitrogen-hydrogensigma bonds
due to sp3-s overlap
Because of this bonding,the H-N-H bond angle
is close to 109.5° (actually 107°).
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04/19/23
The Structure of Ammonia
What bond angle would be expected if thelone pair of electrons didn't affect the structure?
What bond angle would be expected if theatomic orbitals of nitrogen did not hybridize?
Why is the actual bond angle not exactly 109.5°?
Draw the orbital overlap diagram for the reactionof ammonia and a hydrogen ion.
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Groups of ElectronsEdward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
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Groups of Electrons
H
HN
C O
H
Predicts
bond angles
hybridization ofnon-metal atomsin a molecule or ion
Requires
properly drawnLewis Dot
diagram
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04/19/23
Procedure
Draw the proper Lewis Dot diagram. Determine the number of "groups of
electrons" (“effective electron pairs”) around the central atom.• All electrons pointing in the same direction
are considered one group. If only s and p orbitals are involved then the
• correct hybridization and• ideal bond angle is predicted by the number of groups.
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04/19/23
Groupsof
ElectronsHybridization
IdealBondAngle
2 sp 180º
3 sp2 120º
4 sp3 109.5º
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Groups of ElectronsFormamide
H
HN
C O
H
bond angle
hybridization
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04/19/23
Hydrogen Cyanide
CH N
C NH ••••••••••
2 groups of electrons around carbon
sp hybridization H-C-N = 180°
What does the orbitaloverlap diagram look like?
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04/19/23
Hydrogen CyanideC NH ••••••••••
carbonsp hybridized
How many electronsare in each orbital?
nitrogensp hybridized
How many electronsare in each orbital?
hydrogen1s orbital
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04/19/23
Hydrogen CyanideC NH ••••••••••
sigma bondspx orbitaloverlap
py orbitaloverlap
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04/19/23
Hydrogen Cyanide
sigma bonds(between hydrogen and carbon
and carbon and nitrogen)
2 pi bonds
C NH ••••••••••
(between carbonand nitrogen)
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04/19/23
Nitrite Ion
N••••
• •• •O O• •
• •••••
••
N OO
3 groups of electrons around nitrogen
sp2 hybridization O-N-O @ 120°
Why is the bond angleapproximately 120°?
Draw the hybridizedatomic orbitalsfor each atom
O1 sp2 hybridizedO2 sp3 hybridized
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Nitrite IonN••••
• •• •O O• •
• •
••••
••
1s2 2s2 2p4 1s2 2s2 2p3 1s2 2s2 2p4
_ _ _ _ _sp2 p1s
_ _ _ _ _sp2 p1s
_ _ _ _ _sp31s
-1 charge
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Nitrite IonN••••
• •• •O O• •
• •
••••
••
What other kind of bond is formed?
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04/19/23
Nitrite IonN••••
• •• •O O• •
• •••••
••
Where is the pi bond located?
O ON
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04/19/23
Nitrite Ion
N OO
How would the bonding changeif O2 was unhybridized?
N••••
• •• •O O• •
• •••••
•• 3 groups of electrons around nitrogen
sp2 hybridization O-N-O @ 120°
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Nitrite IonN••••
• •• •O O• •
• •
••••
••
1s2 2s2 2p41s2 2s2 2p4
_ _ _ _ _sp2 p1s
1s2 2s2 2p3
_ _ _ _ _sp2 p1s
-1 charge
_ _ _ _ _2p1s 2s
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Nitrite IonN••••
• •• •O O• •
• •
••••
••
What other kind of bond is formed?
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04/19/23
Nitrite IonN••••
• •• •O O• •
• •••••
••
pi bond formation
How could resonance in this molecule be explained?
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04/19/23
EtheneH
HC C
H
H
C••••H••
H••
CH
• •H • •
3 groups of electrons around carbon
sp2 hybridization C-C-H @ 120° H-C-H @ 120°
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04/19/23
EtheneC••••
H
••
H••
CH
• •H • •
How many sigma bonds andhow many pi bonds are formed?
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04/19/23
Ethane
C
H
H
H
C
H
H
H
••C
• •• •
••H
H
H••C
•••• ••H
H
H4 groups of electrons around carbon
sp3 hybridization
C-C-H @ 109.5° H-C-H @ 109.5°
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04/19/23
Ethane••C
• •• •
••H
H
H••C
•••• ••H
H
H
What kind of bonds are formed?
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Dipole MomentsEdward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
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04/19/23
Dipole Moments
Charge is not always equally distributed in a molecule.
There can be a region of positive charge and of negative charge.
The vector connecting these regions is called the dipole moment.
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04/19/23
Dipole Moment
H Cl••
• •• •
Chlorine is more electronegative than hydrogen.
The dipole moment is drawnpositive (+) to negative(-)
(note: physics texts draw it the opposite way!)
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04/19/23
O
••
H
• •
H
Net Dipole Moment
The (net) molecular dipole momentis the vector sum of the individual bond dipoles.
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F BF
FBF
F
F
Canceling Dipole Moments
the net dipolemoment of
boron trifluorideis zero
Sometimes a set ofindividual bondmoments canceleach other.
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Boron Trifluoride
F BF
F
What is thehybridizationof boron in
borontrifluoride?
Can an alternate Lewis Dot diagram be drawn that obeys the octet rule?
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Boron Trifluoride
B••••
• •• •F
F ••••
•• ••
F
••
••••
••
B••••
• •• •F
F ••••
••••
F
••
••••
••
B••••
• •• •F
F ••••
••
F ••••
••••••
What would be the hybridization andbond angles of the resonance structures?
sp2, F-B-F = 120°
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H
CH
HH
Canceling Dipole Moments
the hydrogen atomsin methane arearranged in a
tetrahedral shape
the four vectorscancel
each other
The cancellation ofindividual bond momentscan also occurin three dimensions.
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Carbon Monoxide
C O•• •••• ••••
negative formalcharge
moreelectronegative
Which way does the dipole ofcarbon monoxide point?
Electronegativity and formal chargeboth contribute to the dipole moment.
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Carbon Monoxide
The actual dipole is very small 0.11 D, and points in the direction of carbon!• A debye is 3.336 x 10-30 C·m
C O•• •••• ••••O
••
H
• •
H The dipole moment of thewater molecule is 1.87 D.
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Predictions
For molecular compounds• solubility and miscibility are related to the
polarity (i.e., dipole moment) of the molecule.
"Like dissolves like" is a rule of thumb for solubility• polar molecules dissolve in polar solvents
• nonpolar molecules dissolve in nonpolar solvents
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Carbonate Ion
O C
O
O
2-The concept of dipole momentscan also be applied to ions,although they generallydissolve in polar solvents(e.g., water) becauseof their charge.
Although carbonate ionhas no net dipole moment,
it dissolves in polar solventsbecause of its ionic charge.
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Like Dissolves Like
The rule "like dissolves like" is not perfect; However, it does serve as a starting point in
determining what type of solvent to use when attempting to dissolve a solid.
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Polarity Predictions
Rank the following molecules in terms of polarity:• water, benzene, chloroform
O
••
H
• •
H ClClC
H
Cl
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Polarity Predictions
[Cu(py)2(SCN)2] dissolves in chloroform but not water.• Rationalize this behavior.
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Electronegativity
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Exam 3 Results
0
1
2
3
4
5
6
<60 60-69 70-79 80-89 90-100
Exam 1 Exam 2 Exam3
Nomenclature
Average 89/110 ± 10
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Hardest Question?
Rank the following in order of decreasing melting point: CaS, MgO, KCl
Ionic bonding lattice energy q1 x q2 / r2