2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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November 04, 2016

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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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November 04, 2016

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Formula for Formal Charges

2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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November 04, 2016

Nov 2-7:28 AM

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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November 04, 2016

Nov 2-7:30 AM

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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November 04, 2016

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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)

2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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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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November 04, 2016

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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)

2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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VSEPR Shapes

2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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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

2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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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.

2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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November 04, 2016

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Polar Bonds depend on geometric structure of

the atom and the difference in electronegativity

of the elements in the compounds.

2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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November 04, 2016

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Is Carbon Dioxide a polar molecule?

2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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November 04, 2016

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Is hydrogen sulfide a polar molecule?

2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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November 04, 2016

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How about methane? (CH4

2- Quiz 6, Formal Charges, Exceptions to the Octet, VSEPR, Polar.notebook

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November 04, 2016

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