Chemistry 150
Name(s):
Exercise 2/3: Formal charge, resonance, VSEPR, molecular shapes and polarity
1. One could draw the Lewis dot structure of formic acid as shown below:
Assign formal charges to the structure above and argue why this is not the
preferred structure.
2. a. Draw a legal set of resonance structures for CO2 that involves a triple bond.
b. Assign formal charges to the structures above and argue why this is not the
preferred structure.
3. Use the VSEPR rules to determine and draw the correct Lewis dot structure for
each of the following ions or molecules.
a. H2CO (formaldehyde)
Number of lone pairs =
Number of a†oms bonded to the central atom =
Electron group number (sum of previous two numbers) =
Arrangement of electron groups =
Actual molecular shape (ignoring the lone pairs) =
Ideal central bond angle =
Deviations from ideal bond angle (Y/N)?
b. NOBr
If so, describe with ">" or "<"
Number of lone pairs =
Number of a†oms bonded to the central atom =
Electron group number (sum of previous two numbers) =
Arrangement of electron groups =
Actual molecular shape (ignoring the lone pairs) =
Ideal central bond angle =
Deviations from ideal bond angle (Y/N)?
c. NO2+ (nitrite cation)
If so, describe with ">" or "<"
Number of lone pairs =
Number of a†oms bonded to the central atom =
Electron group number (sum of previous two numbers) =
Arrangement of electron groups =
Actual molecular shape (ignoring the lone pairs) =
Ideal central bond angle =
Deviations from ideal bond angle (Y/N)?
If so, describe with ">" or "<"
d. NO2- (nitrite anion)
Number of lone pairs =
Number of a†oms bonded to the central atom =
Electron group number (sum of previous two numbers) =
Arrangement of electron groups =
Actual molecular shape (ignoring the lone pairs) =
Ideal central bond angle =
Deviations from ideal bond angle?
e. POCl3
If so, describe with ">" or "<"
Number of lone pairs =
Number of a†oms bonded to the central atom =
Electron group number (sum of previous two numbers) =
Arrangement of electron groups =
Actual molecular shape (ignoring the lone pairs) =
Ideal central bond angle =
Deviations from ideal bond angle?
f. SF6 (sulfur hexafluoride)
If so, describe with ">" or "<"
Number of lone pairs =
Number of a†oms bonded to the central atom =
Electron group number (sum of previous two numbers) =
Arrangement of electron groups =
Actual molecular shape (ignoring the lone pairs) =
Ideal central bond angle =
Deviations from ideal bond angle?
If so, describe with ">" or "<"
4. Draw Lewis dot structures for the six species in the previous problem. Then
draw the individual dipole moments along each polar covalent bond. Finally,
draw the net dipole moment for the whole ion or molecule.