Molecular Shape
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Transcript of Molecular Shape
![Page 1: Molecular Shape](https://reader035.fdocuments.in/reader035/viewer/2022062221/5681358d550346895d9cf87b/html5/thumbnails/1.jpg)
Molecular Shape
![Page 2: Molecular Shape](https://reader035.fdocuments.in/reader035/viewer/2022062221/5681358d550346895d9cf87b/html5/thumbnails/2.jpg)
Things to remember
shape of molecule influenced by location of nuclei – nuclei go to certain locations because
of its electron pairs
![Page 3: Molecular Shape](https://reader035.fdocuments.in/reader035/viewer/2022062221/5681358d550346895d9cf87b/html5/thumbnails/3.jpg)
Use the Lewis Structure
• Lewis structure is 2-D, but can help figure out 3-D shape
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Bonding CapacityBonding Capacity
0000:Ne::Ne:Ne, Ar, KrNe, Ar, Kr
2222·O:·O:O, SO, S
3333·N··N·N, PN, P
4444·C··C·C, SiC, Si
1111·F:·F:F, Cl, Br, IF, Cl, Br, I
1111HHH H
Bonding Bonding CapacityCapacity
# Unpaired # Unpaired ElectronsElectrons
Lewis Lewis StructureStructure
AtomAtom
.
..
..
.
......···
··
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Molecular Shape
• Determined by overlap of orbitals
• Shape determined by two factors:
1.1. total # atoms total # atoms & &
2.2. # e# e-- pairs pairs in different locationsin different locations on on central atomcentral atom
classify eclassify e-- pairs as bonding or non-bonding pairs as bonding or non-bonding
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Molecular Shape & VSEPR
• electron pairs repel each other: –want to be as far apart from each other as can be
• non-bonding pairs take up a little more room than bonding pairs
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Orientation of Electron Pairs
tetrahedral: 3-D, 4 e- pairs 109 apart
4
planar Triangular: 3 electron pairs 120 apart
3
linear: 2 electron pairs 180 apart
1 or 2
OrientationTotal # of electron pairs
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2-Atom Molecules
• atoms located next to each other
• linear molecules!
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3-Atom Molecules
• linear or bentlinear or bent
LinearLinear
Bent Bent
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CO2
Lewis structure:Lewis structure: O :: C :: O O :: C :: O....
.... ....
....
4 bonding pairs4 bonding pairsbut onlybut only 2 regions2 regions of electron density: of electron density: 180180 apart so CO apart so CO22 is linear is linear
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Lewis Structure of HLewis Structure of H22O: O: H:O: H:O: HH
....
....H2O
•2 bonding pairs between each O and H2 bonding pairs between each O and H•2 nonbonding pairs on O2 nonbonding pairs on O•4 different regions of electron density4 different regions of electron density
Count up the electron pairs:Count up the electron pairs:
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H2O
• 4 electron pairs are 109 apart
• nonbonding pairs spread out a bit more
– squeeze bonding pairs together so
bent shape
H – O H
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3-Atom Molecules
• Triangular?
Yes, ozone (OYes, ozone (O33) is triangular ) is triangular
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4-Atom Molecules
• Two possibilities:–Trigonal Planar – in 1 plane
–Trigonal Pyramidal
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4-Atom Molecules: Trigonal Planar
Bond angles Bond angles =120=120
All 4 atoms lie in All 4 atoms lie in the same planethe same plane
arenaren’’t likely to see this because theset likely to see this because these molecules molecules dondon’’t obey octet rule!t obey octet rule!
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BF3: Trigonal Planar• B has 3 valence electrons
– very small atom e– each F has 7 valence electrons – total = 3 X 7 + 3 = 24 e-
: F : B : F : B ....
........FF
FF....
....
....
....
.... ........
These molecules These molecules dondon’’t obey octet rule t obey octet rule - so aren- so aren’’t likely to t likely to see themsee them - 3 regions- 3 regions - FBF = 120- FBF = 120
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4-Atom Molecules: AX3
shape most likely to seeshape most likely to see
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NH3
Lewis Structure:Lewis Structure: H : N : H H : N : H
HH
....
....
•3 bonding pairs3 bonding pairs•1 non-bonding pair1 non-bonding pair•4 regions 4 regions •little less than 109little less than 109 apart apart•shape: trigonal pyramidalshape: trigonal pyramidal
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5-Atom Molecules: AX4
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5 Atoms & Tetrahedrons
Tetrahedral means 4 Tetrahedral means 4 faces:faces:- 1 atom in center - 1 atom in center - 4 atoms at the points- 4 atoms at the points
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CH4 = a 5-atom molecule
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CH4
Lewis structure =Lewis structure = H : C : H H : C : HHH
HH........
•4 bonding pairs4 bonding pairs•4 regions of electron density4 regions of electron density•electron pairs are 109electron pairs are 109 apart apart
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CH4 = a 5-atom molecule
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Summary of Molecular Shapes
• start with Lewis Structure!
• look at # regions of e- density on central atom
• look at # atoms bonded to central atom
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Molecular Polarity
• Look at shape of molecule:–non-polar molecular is symmetricalnon-polar molecular is symmetrical
–polar molecular is asymmetricalpolar molecular is asymmetrical
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Molecular Polarity• molecule is symmetric if:
– electrical charge on 1 side is same as electrical charge at matching point on opposite side
–“pull” of one polar bond is offset by “pull” of another polar bond
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Symmetrical Symmetrical Molecules are Molecules are Non-polarNon-polar
NonpolarNonpolar
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AsymmetricAsymmetricMolecules areMolecules arePolarPolar