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Molecular Geometry Chapter 9 AP Chemistry Chapter 9 AP Chemistry

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VSEPR 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.

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Electron 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.

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How many domains does the central atom have in…

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C has 4, N has 4 & O has 3

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Geometry The shapes that molecules take, and thus the angles between bonds, depends on the number of domains. 2 domains need to be 180 o apart to minimize repulsions. 3 Domains need to be 120 o apart. 2 & 3 domains can remain 2-D. Any more domains and it must be 3-D.

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# of domainsArrangementDomain GeometryBond Angles 2linear180 3trigonal planar120 4Tetrahedral109.5 5 Trigonal bipyramidal 120 & 90 6octahedral90

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However, The shape may not match the domain geometry. Why? The shape may not match the domain geometry. Why?

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Domain 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. 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.

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Linear 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:

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Trigonal Planar Domain Geometry option 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:

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Trigonal Planar Domain Geometry option 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:

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Tetrahedral Domain Geometry option 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:

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Tetrahedral Domain Geometry option 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:

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Tetrahedral Domain Geometry option 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:

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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:

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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:

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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:

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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:

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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:

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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:

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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:

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What is the Domain Geometry and the Molecular Geometry of: CO 2 CH 4 XeF 4 H 2 CO CO 2 CH 4 XeF 4 H 2 CO H 2 O XeF 2 PCl 5 ICl 5 H 2 O XeF 2 PCl 5 ICl 5

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Domain Geometry Molecular Geometry CO 2 linear CH 4 tetrahedral XeF 4 octahedralSquare planar H 2 COTrigonal planar H2OH2Otetrahedralbent XeF 2 Trigonal bipyramidal linear PCl 5 Trigonal bipyramidal ICl 5 octahedralSquare pyramidal

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A 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?

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Hybridization 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 sp 3 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 sp 3 hybrid.

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The SP 3 Hybrid On the left are regular p- orbitals and s-- orbital. On the right are the 4 hybrized sp 3 -orbitals.

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More Hybrids When there are 2 domains, there is an SP hybrid. When there are 3 domains, there is an SP 2 hybrid. When there are 4 domains, there is an SP 3 hybrid. When there are 5 domains, there is an SP 3 D hybrid. When there are 6 domains, there is an SP 3 D 2 hybrid. When there are 2 domains, there is an SP hybrid. When there are 3 domains, there is an SP 2 hybrid. When there are 4 domains, there is an SP 3 hybrid. When there are 5 domains, there is an SP 3 D hybrid. When there are 6 domains, there is an SP 3 D 2 hybrid.

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What is the hybridization of the central atom in: CO 2 CH 4 XeF 4 H 2 CO CO 2 CH 4 XeF 4 H 2 CO H 2 O XeF 2 PCl 5 ICl 5

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the hybridization of the central atoms are: CO 2 = SP CH 4 = SP 3 XeF 4 = SP 3 D 2 H 2 CO = SP 2 CO 2 = SP CH 4 = SP 3 XeF 4 = SP 3 D 2 H 2 CO = SP 2 H 2 O = SP 3 XeF 2 = SP 3 D PCl 5 = SP 3 D ICl 5 = SP 3 D 2

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Bonds 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.

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Sigma Bond While this is a depiction of a sigma bond, a sigma bond is not always formed between two s- orbitals.

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Double Bonds Let’s examine a C 2 H 4 molecule. From the Lewis Structure, we expect a double bond. We can also see that carbon has 3 domains, so we expect SP 2 hybridization.

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SP 2 hybridized orbitals bond each carbon atom (and hydrogen atoms) along the axis connecting the atoms, forming bonds. Since SP 2 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. SP 2 hybridized orbitals bond each carbon atom (and hydrogen atoms) along the axis connecting the atoms, forming bonds. Since SP 2 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.

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Triple Bonds Let’s examine a C 2 H 2 molecule. From the Lewis Structure, we expect a triple bond. We can also see that carbon has 2 domains, so we expect SP hybridization.

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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.

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Can you figure out… How many pi bonds and how many sigma bonds are present (in total) in the molecule below?

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Remember 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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