Chapter 3 Simple Bonding Theory Lewis Dot Structures – Resonance – Formal Charge VSEPR: the subtle…
Formal Charges of Lewis Structures In order to determine...
Transcript of Formal Charges of Lewis Structures In order to determine...
2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook
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Formal Charges of Lewis Structures
In order to determine the best Lewis Structure,
the formal charges of each element must be
calculated, an ideal structure has an overall
formal charge of 0 with each element having a
formal charge of 0.
2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook
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Formula for Formal Charges
2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook
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Draw the Lewis structure and determine the
formal charges of each
H2O CO2 NH4+
2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook
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Using the idea of formal charges, draw the
resonance structures of CO2 and determine
which is the best.
2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook
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Exceptions to the Octet Rule in Lewis structures
1) Species with odd number of electrons
-free radicals
example: NO (nitrogen monoxide)
2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook
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2) Incomplete octets
-beryllium, aluminum, boron
Example: BH3 (Borane, boron trihydride)
Example: BF3 (boron triflouride)
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3) Expanded Octet
-only elements with a minimum of n=3 can
have expanded octets
Example: SF6 (sulfur hexafluoride)
Example: SO42- (sulfate)
You must look at the resonance structures
and determine which has better formal
charges.
2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook
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Practice
1) Draw the Lewis structure for the molecule I3-
2) Draw the molecule ClF3
3) The central atom for an expanded octet must
have an atomic number larger than what?
4) Draw the Lewis structure for NO2
5) Which Lewis structure is more likely?
2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook
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1) 2)
3) 10 (sodium or higher)
4)
5)
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VSEPR Shapes
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Bond angles
linear = 180 o
trigonal planar = 120o
bent / angular = <120o
H20 is 104.5o, SO2o
tetrahedral = 109.5o
trigonal pyramidal = 107o
trigonal bipyramidal = 90o , 120o , 180o
octehdral = 90o , 180o
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Polar Bonds
Because of this, one end of the molecule has
a slightly negative charge and the other a
slightly positive charge.
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Polar Bonds depend on geometric structure of
the atom and the difference in electronegativity
of the elements in the compounds.
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Is Carbon Dioxide a polar molecule?
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Is hydrogen sulfide a polar molecule?
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How about methane? (CH4
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