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VSEPRVSEPR
Valence Shell Electron Pair Repulsions
Electrons are negatively charged, so each pair will repel other pairs such that they spread out in 3-D space to minimize the repulsions.
Valence Shell Electron Pair Repulsions
Electrons are negatively charged, so each pair will repel other pairs such that they spread out in 3-D space to minimize the repulsions.
Electron DomainsElectron Domains
Domains are regions about an atom’s shell where electrons are concentrated.
This is easier to see with a Lewis diagram.
For example, the carbon atom above has electrons on two sides (even though they are double bonds). So this carbon atom has 2 domains.
Domains are regions about an atom’s shell where electrons are concentrated.
This is easier to see with a Lewis diagram.
For example, the carbon atom above has electrons on two sides (even though they are double bonds). So this carbon atom has 2 domains.
GeometryGeometry
The shapes that molecules take, and thus the angles between bonds, depends on the number of domains.
The shapes that molecules take, and thus the angles between bonds, depends on the number of domains.
2 domains need to be 180o apart to minimize repulsions.
3 Domains need to be 120o apart.
2 & 3 domains can remain 2-D. Any more domains and it must be 3-D.
2 domains need to be 180o apart to minimize repulsions.
3 Domains need to be 120o apart.
2 & 3 domains can remain 2-D. Any more domains and it must be 3-D.
# of domains Arrangement Domain Geometry Bond Angles
2 linear 180
3 trigonal planar 120
4 Tetrahedral 109.5
5Trigonal
bipyramidal120 & 90
6 octahedral 90
However,However,
The shape may not match the domain geometry.
Why?
The shape may not match the domain geometry.
Why?
Domain Geometry vs Molecular GeometryDomain Geometry vs Molecular Geometry
In the Lewis Structure of water, we see 4 domains. Yet when we look at a water molecule, we can only see the bonds, not the nonbonding pairs.
In the Lewis Structure of water, we see 4 domains. Yet when we look at a water molecule, we can only see the bonds, not the nonbonding pairs.
Look back at the angles.
4 domains should have an angle of 109.5.
The water molecule is 104.5.
These angles are too close to be coincidence.
Look back at the angles.
4 domains should have an angle of 109.5.
The water molecule is 104.5.
These angles are too close to be coincidence.
Linear Domain GeometryLinear Domain Geometry
There are 2 domains There are Zero nonbonding domains.
The Molecular Geometry is linear
Example:
There are 2 domains There are Zero nonbonding domains.
The Molecular Geometry is linear
Example:
Trigonal Planar Domain Geometryoption 1
Trigonal Planar Domain Geometryoption 1
There are 3 domains If there is Zero nonbonding domains, then The Molecular Geometry is trigonal planar
Example:
There are 3 domains If there is Zero nonbonding domains, then The Molecular Geometry is trigonal planar
Example:
Trigonal Planar Domain Geometryoption 2
Trigonal Planar Domain Geometryoption 2
There are 3 domains If there is 1 nonbonding domain, then The Molecular Geometry is bent
Example:
There are 3 domains If there is 1 nonbonding domain, then The Molecular Geometry is bent
Example:
Tetrahedral Domain Geometryoption 1
Tetrahedral Domain Geometryoption 1
There are 4 domains If there is Zero nonbonding domains, then The Molecular Geometry is tetrahedral
Example:
There are 4 domains If there is Zero nonbonding domains, then The Molecular Geometry is tetrahedral
Example:
Tetrahedral Domain Geometryoption 2
Tetrahedral Domain Geometryoption 2
There are 4 domains If there is 1 nonbonding domain, then The Molecular Geometry is trigonal pyramidal
Example:
There are 4 domains If there is 1 nonbonding domain, then The Molecular Geometry is trigonal pyramidal
Example:
Tetrahedral Domain Geometryoption 3
Tetrahedral Domain Geometryoption 3
There are 4 domains If there are 2 nonbonding domains, then The Molecular Geometry is bent
Example:
There are 4 domains If there are 2 nonbonding domains, then The Molecular Geometry is bent
Example:
Trigonal Bipyramidal Domain Geometry option 1
Trigonal Bipyramidal Domain Geometry option 1
There are 5 domains If there are zero nonbonding domains, then The Molecular Geometry is trigonal bipyramidal
Example:
There are 5 domains If there are zero nonbonding domains, then The Molecular Geometry is trigonal bipyramidal
Example:
Trigonal Bipyramidal Domain Geometry option 2
Trigonal Bipyramidal Domain Geometry option 2
There are 5 domains If there is 1 nonbonding domain, then The Molecular Geometry is SeeSaw
Example:
There are 5 domains If there is 1 nonbonding domain, then The Molecular Geometry is SeeSaw
Example:
Trigonal Bipyramidal Domain Geometry option 3
Trigonal Bipyramidal Domain Geometry option 3
There are 5 domains If there are 2 nonbonding domains, then The Molecular Geometry is T-Shaped
Example:
There are 5 domains If there are 2 nonbonding domains, then The Molecular Geometry is T-Shaped
Example:
Trigonal Bipyramidal Domain Geometry option 4
Trigonal Bipyramidal Domain Geometry option 4
There are 5 domains If there are 3 nonbonding domains, then The Molecular Geometry is linear
Example:
There are 5 domains If there are 3 nonbonding domains, then The Molecular Geometry is linear
Example:
Octahedral Domain Geometry option 1
Octahedral Domain Geometry option 1
There are 6 domains If there are zero nonbonding domains, then The Molecular Geometry is octahedral
Example:
There are 6 domains If there are zero nonbonding domains, then The Molecular Geometry is octahedral
Example:
Octahedral Domain Geometry option 2
Octahedral Domain Geometry option 2
There are 6 domains If there is 1 nonbonding domain, then The Molecular Geometry is square pyramidal
Example:
There are 6 domains If there is 1 nonbonding domain, then The Molecular Geometry is square pyramidal
Example:
Octahedral Domain Geometry option 3
Octahedral Domain Geometry option 3
There are 6 domains If there are 2 nonbonding domains, then The Molecular Geometry is square planar
Example:
There are 6 domains If there are 2 nonbonding domains, then The Molecular Geometry is square planar
Example:
What is the Domain Geometry and the
Molecular Geometry of:
What is the Domain Geometry and the
Molecular Geometry of:
CO2
CH4
XeF4
H2CO
CO2
CH4
XeF4
H2CO
H2O
XeF2
PCl5
ICl5
H2O
XeF2
PCl5
ICl5
Domain Geometry
Molecular Geometry
CO2 linear linear
CH4 tetrahedral tetrahedral
XeF4 octahedral Square planar
H2CO Trigonal planar
Trigonal planar
H2O tetrahedral bent
XeF2 Trigonal bipyramidal
linear
PCl5 Trigonal bipyramidal
Trigonal bipyramidal
ICl5 octahedral Square pyramidal
A thought QuestionA thought Question
The Electron Dot Structure of Carbon shows four unpaired electrons, but the Orbital Notation only shows 2. Why?
* *C* *
Will carbon make 2 bonds, or 4?
The Electron Dot Structure of Carbon shows four unpaired electrons, but the Orbital Notation only shows 2. Why?
* *C* *
Will carbon make 2 bonds, or 4?
HybridizationHybridization
Bonding usually involves s-orbitals. For the s-orbital of carbon to bond, one of the electrons has to go somewhere.
That somewhere is the empty p orbital. In order to make 4 bonds, the carbon will combine its s-orbital with its 3 p-orbitals into a new set of 4 orbitals all of equal energy.
This new set is called a hybrid and is referred to as an sp3 hybrid.
Bonding usually involves s-orbitals. For the s-orbital of carbon to bond, one of the electrons has to go somewhere.
That somewhere is the empty p orbital. In order to make 4 bonds, the carbon will combine its s-orbital with its 3 p-orbitals into a new set of 4 orbitals all of equal energy.
This new set is called a hybrid and is referred to as an sp3 hybrid.
The SP3 HybridThe SP3 Hybrid
On the left are regular p-orbitals and s--orbital.
On the left are regular p-orbitals and s--orbital.
On the right are the 4 hybrized sp3-orbitals.
On the right are the 4 hybrized sp3-orbitals.
More HybridsMore Hybrids
When there are 2 domains, there is an SP hybrid.
When there are 3 domains, there is an SP2 hybrid.
When there are 4 domains, there is an SP3 hybrid.
When there are 5 domains, there is an SP3D hybrid.
When there are 6 domains, there is an SP3D2 hybrid.
When there are 2 domains, there is an SP hybrid.
When there are 3 domains, there is an SP2 hybrid.
When there are 4 domains, there is an SP3 hybrid.
When there are 5 domains, there is an SP3D hybrid.
When there are 6 domains, there is an SP3D2 hybrid.
What is the hybridization of the
central atom in:
What is the hybridization of the
central atom in:
CO2
CH4
XeF4
H2CO
CO2
CH4
XeF4
H2CO
H2O
XeF2
PCl5
ICl5
H2O
XeF2
PCl5
ICl5
the hybridization of the central atoms are:
the hybridization of the central atoms are:
CO2 = SP
CH4 = SP3
XeF4 = SP3D2
H2CO = SP2
CO2 = SP
CH4 = SP3
XeF4 = SP3D2
H2CO = SP2
H2O = SP3
XeF2 = SP3D
PCl5 = SP3D
ICl5 = SP3D2
H2O = SP3
XeF2 = SP3D
PCl5 = SP3D
ICl5 = SP3D2
BondsBonds Earlier, we stated that bonding usually involves an s-orbital. How does that happen?
When 2 s-orbitals overlap, the electro-static forces of attraction of the nucleus of one atom will attract the electrons of the other atom and vice versa, forming a bond.
If two s-orbitals directly overlap then the bond formed is linear between the 2 nuclear centers & is called a sigma () bond.
Earlier, we stated that bonding usually involves an s-orbital. How does that happen?
When 2 s-orbitals overlap, the electro-static forces of attraction of the nucleus of one atom will attract the electrons of the other atom and vice versa, forming a bond.
If two s-orbitals directly overlap then the bond formed is linear between the 2 nuclear centers & is called a sigma () bond.
Sigma BondSigma Bond
While this is a depiction of a sigma bond, a sigma bond is not always formed between two s-orbitals.
While this is a depiction of a sigma bond, a sigma bond is not always formed between two s-orbitals.
Double BondsDouble Bonds
Let’s examine a C2H4 molecule. Let’s examine a C2H4 molecule. From the Lewis Structure, we expect a double bond. We can also see that carbon has 3 domains, so we expect SP2 hybridization.
From the Lewis Structure, we expect a double bond. We can also see that carbon has 3 domains, so we expect SP2 hybridization.
SP2 hybridized orbitals bond each carbon atom (and hydrogen atoms) along the axis connecting the atoms, forming bonds.
Since SP2 uses 3 orbitals, we see that there is an unhybridized P-orbital.
As the bond forms, the atoms move closer and the p-orbitals of the 2 carbons merge into a 2nd bond called a pi () bond.
The top and bottom portion are both part of the same bond.
SP2 hybridized orbitals bond each carbon atom (and hydrogen atoms) along the axis connecting the atoms, forming bonds.
Since SP2 uses 3 orbitals, we see that there is an unhybridized P-orbital.
As the bond forms, the atoms move closer and the p-orbitals of the 2 carbons merge into a 2nd bond called a pi () bond.
The top and bottom portion are both part of the same bond.
Triple BondsTriple Bonds
Let’s examine a C2H2 molecule. Let’s examine a C2H2 molecule.
From the Lewis Structure, we expect a triple bond. We can also see that carbon has 2 domains, so we expect SP hybridization.
From the Lewis Structure, we expect a triple bond. We can also see that carbon has 2 domains, so we expect SP hybridization.
SP hybridized orbitals bond each carbon atom (and hydrogen atoms) along the axis connecting the atoms, forming bonds.
Since SP uses 2 orbitals, there must be 2 unhybridized P-orbitals.
As the bond forms, the atoms move closer and the p-orbitals of the 2 carbons merge into 2 pi () bonds.
SP hybridized orbitals bond each carbon atom (and hydrogen atoms) along the axis connecting the atoms, forming bonds.
Since SP uses 2 orbitals, there must be 2 unhybridized P-orbitals.
As the bond forms, the atoms move closer and the p-orbitals of the 2 carbons merge into 2 pi () bonds.
Can you figure out…Can you figure out…
How many pi bonds and how many sigma bonds are present (in total) in the molecule below?
How many pi bonds and how many sigma bonds are present (in total) in the molecule below?
QuickTime™ and a decompressor
are needed to see this picture.
RememberRemember
A single bond consist of 1 sigma bond.
A double bond consist of 1 sigma bond and 1 pi bond.
A triple bond consist of 1 sigma bond and 2 pi bonds.
So the answer to the last question is 11 sigma bonds and 1 pi bond.
A single bond consist of 1 sigma bond.
A double bond consist of 1 sigma bond and 1 pi bond.
A triple bond consist of 1 sigma bond and 2 pi bonds.
So the answer to the last question is 11 sigma bonds and 1 pi bond.
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