Formal Charges and Exceptions to the Octet.notebook
November 04, 2015
Warm up
Draw the Lewis Structure for HCN
Nov 2-7:25 AM
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.
Nov 2-7:25 AM
Formal Charges and Exceptions to the Octet.notebook
November 04, 2015
Formula for Formal Charges
Valence electrons - bonds - loan electrons
Nov 2-7:27 AM
Draw the Lewis structure and determine the
formal charges of each
H2O
CO2
Nov 2-7:28 AM
NH4+
Formal Charges and Exceptions to the Octet.notebook
November 04, 2015
Using the idea of formal charges, draw the
resonance structures of CO2 and determine
which is the best.
Nov 2-7:30 AM
Exceptions to the Octet Rule in Lewis structures
1) Species with odd number of electrons
-free radicals
example: NO (nitrogen monoxide)
Nov 2-7:36 AM
Formal Charges and Exceptions to the Octet.notebook
November 04, 2015
2) Incomplete octets
-beryllium, aluminum, boron
Example: BH3 (Borane, boron trihydride)
Example: BF3 (boron triflouride)
Nov 2-7:40 AM
3) Expanded Octet
-only elements with a minimum of n=3 can
have expanded octets
Example: SF6 (sulfur hexaflouride)
Example: SO42- (sulfate)
You must look at the resonance structures
and determine which has better formal
charges.
Nov 2-7:45 AM
Formal Charges and Exceptions to the Octet.notebook
November 04, 2015
Practice
1) Draw the Lewis structure for the molecule I32) 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?
Nov 2-7:48 AM
1)
2)
3) 10 (sodium or higher)
4)
5)
Nov 2-7:56 AM
Formal Charges and Exceptions to the Octet.notebook
Nov 2-7:58 AM
Nov 3-12:08 PM
November 04, 2015