CH 115 Fall 2014
Worksheet 9
1. What is the formula for calculating formal charge? Why do we calculate formal
charge?
Formal charge = (number of valence electrons) – (number of lone pair
electrons) – (1/2* number of bonding electrons) OR (number of bonds)
We calculate formal charge in order to determine which of the Lewis
structures we have drawn for a compound (if multiple are possible) is the
best. Remember that 0 is the best formal charge for any atom to have. Negative
numbers are better than positive numbers – formal charge is better when the
negative charge is on the most electronegative of the atoms. The formal charge
of each atom must add up to the total charge on the compound.
2. Draw the Lewis structure(s) for each of the following compounds. Include all
resonance structures if applicable and calculate formal charge for each of the atoms.
a). CH2CHF
b). H2NCOCH3
c). O3
d). NH4+