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04/18/23
One Point Quiz
One quiz per table, list everyone’s name Agree on an answer You have two minutes
Molecular Orbital TheoryEdward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
04/18/23
Bonding Theories
Ionic Model Skeleton Diagrams Lewis Dot Diagrams
• Formal Charge, Resonance Molecular Orbital Theory
• Extends atomic orbitals concepts to molecules
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Bonding in Diatomic Molecules
••B• •
• •••A+
Ionic bonding
Diatomic: molecule contains two atoms
large difference inelectronegativity
Covalent bonding
••D
• •• •
••C
• •• •
••
small difference inelectronegativity
Give an example of a compound with ionic bonding.
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Homodiatomic MoleculesThe best example of covalent bonding
involves homodiatomic molecules.
Contains two of the same type of atom.
e.g., H2, O2, F2, N2
Why are these molecules the best examplesof covalent bonding?
••A• •
• •
••A• •
• •••
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Homodiatomic MoleculesThe best example of covalent bonding
involves homodiatomic molecules.
Contains two of the same type of atom.
e.g., H2, O2, F2, N2
Why are these molecules the best examplesof covalent bonding?
Bonding electrons are exactly shared becauseboth atoms have the same electronegativity.
••A• •
• •
••A• •
• •••
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Heterodiatomic Molecules
H - F
positive end negative end
HF, BN and CO are heterodiatomic molecules.
Contain two different atoms.
These molecules are polar covalent.
What factors might help predict the positiveand negative ends of the molecule?
A Little Review
What is an orbital?
What is the maximum number of electronsthat can be in one orbital?
What is the name of the mathematical functionthat determines the shape of an orbital?
Give an example of an atomic orbital?
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Molecular Orbitals
When two atoms come close to each other,
what happens to the orbitals of each atom?
a bond forms1s atomic
orbital1s atomic
orbitals
b molecularorbital
sigma s bonding molecular orbital
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Molecular Orbitals
Orbital wave functionscan add & subtract to givenew wave functions andcorrespondingmolecular orbitals (mo).
Atoms bondtogether when
the wave functionsconstructively overlap.
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SIGMA BOND ()
A bond between two atoms in which the electrondensity of the molecular orbital is between the
two nuclei is called a sigma bond.
(sb)2 molecular
orbital
nuclei
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Molecular Orbitals (mo)
Obey many of the same rules as atomic orbitals (ao).• two electrons per molecular orbital.• specific regions of space.• one molecular orbital formed for each
atomic orbital used.
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Wave Functions
The amplitude (height) of each wavefunctioncan either be positive or negative.
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WavefunctionsBonding & Antibonding Orbitals
b
Constructively interfere in certain regions of space.
*
Destructively interfere in certain regions of space.
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Bonding & Antibonding Orbitals
H H
sb
s*
When a bondingmolecular orbital forms,
an antibondingmolecular orbital
also forms.
Bonds form where orbitals overlap and electrons are.
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Atomic and Molecular Orbitals
xy
z
1s 2py3dz2
Atomic orbitals include
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Atomic and Molecular Orbitals
sb
z
z*x*x
y
Molecular orbitals include
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Atomic and Molecular Orbitals
This represents an orbital
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Atomic and Molecular Orbitals
ener
gy
An orbital can be emptyor can contain
1 or 2 electrons.
Orbitalscan havedifferent energies
carbon: 1s2 2s2 2p2
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Molecular Orbital Diagrams
Examples• dihydrogen• dihelium• dihelium(I) ion• dilithium• dilithium(I) ion• dilithate ion
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Dihydrogen, H2
1s1 hydrogen orbitalof two hydrogen atoms
Two 1s1 hydrogen orbitalsoverlap to form a s
b bonding molecular orbital
H Hs
bener
gy
s*
The branch lines indicate whichatomic orbitals are involved in
generating the molecular orbitals.
H H
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moao ao
Dihydrogen, H2
sben
ergy
s*
Dihydrogen is diamagneticand contains one bond
(one pair of bonding electrons).
H H
What advantage canan orbital gain in forminga molecular orbital from
an atomic orbital?
electronic configurationof the hydrogen molecule.
(sb)2
Why is dihydrogendiamagnetic?
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Each helium atomhas the electronicconfiguration 1s2
(each contributes2 electrons to the helium
molecular orbitals)
Dihelium, He2en
ergy
atomic orbitalof one He atom
atomic orbitalof the other
He atom
sb
s*Two electrons occupy
the highest molecular orbitalforming a s*
Two electrons occupythe lowest molecular orbital
forming a sb
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Dihelium, He2
The electronic configurationof the dihelium molecule is
(sb)2 (s*)2
ener
gy
sb
s* Why doesn’t He2 existas a stable molecule?
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Dihelium, He2
The electronic configurationof the dihelium molecule is
(sb)2 (s*)2
ener
gy
sb
s* Why doesn’t He2 existas a stable molecule?
Antibonding implies there is a “negative” bond1 bond + 1 antibond = zero net bonds
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Dihelium(I) Ion, He2+
ener
gy
How many valence electrons must be consideredin the dihelium(I) ion?
He He+
Complete the molecular orbital diagram using the available electrons.
sb
s*He He
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Dihelium(I) Ion, He2+
ener
gy
Linedmeans 1
He He+
These representthe atomic orbitals.
Shaded means2 electrons
sb
s*
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Dihelium(I) Ion, He2+
ener
gy
Draw an outline of the molecular orbitals.Fill-in the molecular orbitals,shaded for 2 electrons, lined for 1.
He He+
sb
s*
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Dihelium(I) Ion, He2+
The sigma bonding orbital contains two electrons,the sigma antibonding orbital contains one electron.
What is the electronic configuration of thedihelium(I) ion?
(sb)2 (s*)1
ener
gy
sb
s*
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What physical propertiesare predicted for the
dihelium(I) ion?
ener
gy
sb
s*
(magnetic and bond order)
Dihelium(I) Ion, He2+
Dilithium Molecule
“Beam me up, Scotty”
“I can’t sir, it’s … the dilithiumcrystals …”
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Dilithium Molecule, Li2
Each lithium atom has the electronic configuration 1s2 2s1.• The 2s orbitals of the lithium atoms overlap
well.
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Dilithium Molecule, Li2
The 1s orbitals are much smaller (r n2) and do not overlap well.• These orbitals do not substantially
contribute to the bonding in this molecule.
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Dilithium, Li2en
ergy
2s
1s
There is no gainin stability or
lowering of energy.These are
nonbonding orbitals (1sn)
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Dilithium, Li2en
ergy
The 2s orbitals constructively overlap and form asigma bonding molecular orbital (s
b).
2s
1s
sb
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Dilithium, Li2en
ergy
The 2s orbitals destructively overlap and form asigma antibonding molecular orbital (s*).
2s
1s
s*
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Dilithium, Li2en
ergy
(sn)4 (s
b)2
or(s
b)2
2s
1s
(sn)4
Often the inner shellnonbonding electronsare not listed for the
molecular orbital.
Generally,only outer shell
(valence) electronsare involved in bonding.(s
b)2
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Dilithium, Li2en
ergy
What physical propertiesare predicted for
dilithium?
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Dilithium(I) Ion, Li2+
ener
gy
one valenceelectron2s
1s
Only orbitals whichoverlap are considered
electronic configuration
sb
(sb)1
bond order? 1/2
magnetic property?
one unpaired electronparamagnetic
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Dilithium(I) Ion, Li2+
ener
gy
2s
sb
atomic orbitalsoverlap molecular orbitals
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s*
sb
2s
LiLi2–Li–
1s
Dilithate Ion, Li2–
ener
gy (sb)2 (s*)1
magnetic property?
1 unpairedelectron
paramagnetic
bonding electronicconfiguration?
bond order?
4 nonbonding e–
2 bonding e–
1 antibonding e–
bond order 0.5
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Dilithate Ion, Li2–
Draw the molecular orbitals involved in bonding. • Shaded orbital for two electrons.• Lined orbital for one electron.• Open orbital for no electrons.
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Dilithate Ion, Li2–
(sb)2 (s*)1
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Compare and Contrast
How would the bond lengths of the variousdilithium species be expected to vary?
dilithium, Li2dilithium(I) ion, Li2+
dilithate ion, Li2–
bond order 1
bond order 0.5
bond order 0.5
Li2 < Li2+ Li2–
Lithium Hydride
What would the orbital overlap and molecular orbital diagram look like
for lithium hydride?
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04/18/23
Unknown Dues Dates
Unknown AFriday, Week 5 Unknown BFriday, Week 7 Unknown C Friday, Week 9 Unknown D Friday, Week 10
04/18/23
Extra Period Laboratory
Monday, April 27
1:35 - 4:15 pm
Especially For Those Who Cannot
Attend Any Other Extra Period
No Sign Up Needed
First Come Basis
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