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Slide1
s and p BondsMO TheorySlide2
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Answering QuestionsReview Question: How do you know when to move the order of the elements when listing the ionization energy?
Does one of them have a stable electron configuration (half filled or fully filled)?
Why does the anti bonding orbital has an additional node between the nuclei and is called the pi*2p orbital
?Are nodes and lobes the same thing?
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MO Theory: s orbitals
E
isolated H
atoms
Bonding MO, σ
1s
Anti-bonding MO,
σ
*
1s
1s
-
1s
1s
+
1s
s orbitals form
s
and
s
* molecular orbitals
Add
and subtract orbitals to get the bonding and
anti-bonding
orbitals
Start with 2 atomic s orbitals end with 2 molecular orbitals.
Fill in electrons from low to high energy, just like in atomic orbital diagrams
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MO Theory: p orbitals
End to end
overlap
Side to sideoverlap
p
orbitals form
s
and
s
* molecular orbitals or
p
and
p
* orbitals depending on type of overlap
Add
and subtract orbitals to get the bonding and
anti-bonding orbitals
Start with 6 atomic orbitals end with 6 molecular orbitals
Fill in electrons from low to high energy, just like in atomic orbital diagrams
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PracticeDraw the molecular orbital diagram for nitrogen. Is it paramagnetic or diamagnetic?
What is the bond order?
Hint: ½(bonding electron-
antibonding electrons)What would happen to the bond order if you added an electron? The bond length?What would happen to the bond order if you subtracted an electron? The bond length?
E
Diamagnetic
Bond Order: ½(8-2)=
3
Adding electron: adds to
antibonding
orbital so it would subtract from the bond order making it longer.
subtracting electron: subtracts from bonding orbital, lowering bond order, making the bond longer
N
N
2p
N
2
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PracticeDraw the molecular orbital diagram for fluorine. Is it paramagnetic or diamagnetic?
What is the bond order?
Hint: ½(bonding electron-
antibonding electrons)What does adding an electron do to the bond order? To the bond length?What does subtracting an electron do to the bond order? To the bond length?
Ediamagnetic
Bond Order: ½(8-6)=1Adding electron: adds to antibonding orbital so it would subtract from the bond order making the bond longer.
subtracting electron: subtracts from an anti-bonding orbital, increasing the bond order, making the bond shorter
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PracticeThe ground-state electron configuration of the ion C2
n-
is
s2s2s2s*2p2p4
s2p2.What is the charge on the anion?Draw the MO diagram. Is it paramagnetic or diamagnetic? What is the bond order?Hint: ½(bonding electron-antibonding electrons)Would adding an electron add or subtract from the bond order?
Would subtracting an electron make the bond longer or shorter?Charge= -2Carbon 4+4=8 valence electrons is neutral10 present so -2 charge
E
Diamagnetic
Bond Order: ½(8-2)=
3
Adding electron: adds to
antibonding
orbital so it would subtract from the bond order
subtracting electron: subtracts from bonding orbital, lowering bond order, making the bond longer
C
-
C
-
C
2
2-
2p
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Heteronuclear PracticeFor CN the energy of the molecular orbitals follows the order of carbon (a.k.a.
p
2p
<s2p)Draw the MO diagram. Give the valence shell electron configurations of CN and CN-.Are they paramagnetic or diamagnetic?Tell the bond order of each.
Which has the stronger bond?
E
C
N
CN
E
C
N
CN
-
s
2s
2
s
2s
*2
p
2p
4
s
2p
1
s
2s
2
s
2s
*2
p
2p
4
s
2p
2
p
aramagnetic
diamagnetic
Bond order= ½ (7-2)=2.5
Bond order= ½ (8-2)=
3
Stronger!
2p
2p
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PracticeConsider the hypothetical species HeH. What charge, if any, should be present on this combination of atoms to produce the most stable molecule or ion possible?
Draw the MO diagram for the neutral species first.
Decide what ion gives largest bond order
What is the bond order on the neutral species and what bond order, if changed, is on the ion you chose?
He
H
HeH
Neutral
B.O.= ½(2-1)=0.5
Maximum bond order if you remove electron from
antibonding
orbital.
Gives +1 ion
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PracticeIf the charge on the neutral species were increased or decreased by one what would be the affect on the bonding of the atom.
If the charge on
the species you chose were
increased or decreased by one what would be the affect on the bonding of the atom.
He
H
HeH
+1
B.O.= ½ (2)=1
He
H
HeH
Neutral
B.O.= ½(2-1)=0.5
Neutral:
If charge was increased: remove from
antibonding
giving higher bond order.
If charge decreased: add electron to
antibonding
giving lower bond order.
+1:
If charge was increased: remove from bonding giving lower bond order.
If charge decreased: add electron to
antibonding
giving lower bond order.
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