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Molecular Geometry Chapter 9 AP Chemistry

Molecular Geometry Chapter 9 AP Chemistry Chapter 9 AP Chemistry

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Molecular Geometry

Chapter 9AP Chemistry

Chapter 9AP Chemistry

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.

How many domains does the central atom have

in…

How many domains does the central atom have

in…

C has 4, N has 4 & O has 3

C has 4, N has 4 & O has 3

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.