dr. s. m. condren chapter 10 molecular structures
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Dr. S. M. Condren
Chapter 10
Molecular Structures
Dr. S. M. Condren
Dr. S. M. Condren
What is the “shape” of the molecule?
• How are valence electrons in a molecule distributed among the orbitals?
• What are the shapes of these orbitals?
• What order are they occupied?
Dr. S. M. Condren
Molecular GeometryVSEPR Theory
Valence Shell Electron Pair Repulsion Theory
• draw Lewis electron dot structure
• count the number of bonding electron pairs about central atom (double and triple bonds count as one pair for shape prediction)
• count the number of lone pairs of electrons
• match electron pair information to shapes
Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
Shape: PCl3
Lewis Electron Dot Structure .. .. ..:Cl P : Cl: .. .. .. :Cl: ..
3 bond pairs1 lone pair => AB3E
trigonal pyramidal shape
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Shape: IF5
Lewis Electron Dot Structure
.. ..
: F : : F : .. .. .. : I : F : .. .. .. : F : :F :
.. ..
5 bonds pairs1 lone pair => AB5E
Square pyramidal shaped
Dr. S. M. Condren
Shape: IF4-1
Lewis Electron Dot Structure
.. .. -1
: F : : F : .. .. .. : I : F : .. .. .. : F :
..
4 bond pairs2 lone pairs => AB4E2
square planar shape
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Shape: SO3
Lewis Electron Dot Structure
.. : O : S : : O : .. .. .. : O :
..
3 bond pairs
0 lone pairs => AB3
trigonal planar shape
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What would be expected to be the shape of chloroform, CHCl3?
“see-saw”
square planar
tetrahedral
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http://www.colby.edu/chemistry/OChem/DEMOS/Orbitals.html
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Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
What would be the name of the hybrid orbitals created by joining 1s type, 3 p type and 2 d type orbitals?
spd
sp3d2
s3p2d
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Sigma Bond Bond with the greatest electron density on a line connecting the atomic nuclei
s-s type p-p type s-p type
s-sp3 type s-sp2 type s-sp type
p-sp3 type p-sp2 type p-sp type
sp3 - sp3 type sp2-sp2 type sp - sp type
etc., including all combinations of s, p, d, and hybrid orbitals
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Dr. S. M. Condren
Dr. S. M. Condren
Pi Bond
Bond with the greatest electron density above and below a line connecting the atomic nuclei
p-p type
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Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
Water, H2O, and methane, CH4, have very similar molar masses yet the boiling point for water is approximately 200oC higher than that for methane. The higher boiling point is due to:
hydrogen bonding in water
polarity of water molecules
both of the above
none of the above
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Carbon monoxide, CO and carbon dioxide, CO2, are linear molecules. Which one is the polar molecule:
CO
CO2
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Dr. S. M. Condren
http://mrsec.wisc.edu/edetc/DNA.htm
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Dr. S. M. Condren
Dr. S. M. Condren
In DNA, thymine always links to adenine and cytosine always links to guanine. This is due to:
one is a base and the other an acid
number of hydrogen bonds each can form
one is attached to a sugar and the other a phosphate
Dr. S. M. Condren