1.
Give the Lewis structure and formal charges for Ethanol (C
2
H
5
OH)
Formal charge= # of valence electrons – (# of lone pair electrons + # of bonds). In this structure the carbons are equal because they both have same # of bonds so: Carbon= 4 – (0+4)=0 and oxygen= 6 – (4+2)= 0 so this is a neutral molecule.
2.
Give the Lewis structure, formal charge, and any resonance contributes for phosphate ion. Which resonance contributor(s) are the most prevalent (stable)
These are the most stable forms of phosphate ion. In these resonance structres the formal charges on the oxygens and phosphorus are minimized. Small charges are more stable than larger charges.
P: 5 – (0+5)=0; the three single bond oxygens: 6 – (6+1) = -1; 2x bonded oxygen: 6 – (6+1)= -1
Adds up to the -3 charge of the phosphate ion.
3.
Give the Lewis structure, formal charge, and any resonance contributes for phosgene
(COCl
2
). Which resonance contributor(s) is/are the most prevalent (stable)
In Good resonance: C: 4 – ( 0+4)= 0; Oxygen: 6 – (4+2)= 0; 2 Cl: 7 – (6+1)=0
In Bad resonance: C: 4- (0+3)= 1; Oxygen: 6 – (6+1) = -1; 2 Cl: 7 – (6+1)=0
The good resonance has the charges on each atom minimized AND carbon has its octet filled; in bad resonance, the charges are larger and carbon does not have its octet. Oxygen donates electrons (not chlorine) because oxygen can form two bonds (needs 2 electrons) to get an octet while chlorine prefers to only form one bond.

4.
Give the Lewis structure, resonance structure, formal charge for nitrogen dioxide, NO
2
.
Where are the positive and negative charges located in this molecule?
Formal charge for the atoms shown:
N: 5 – [1+3)=1
O
1
:6- (6+1)= -1
O
2
: 6 – (4+2)=0
5.
Give the Lewis structure for CO
2
. Does it have any resonance structures?
*The carbons are not shown* but the structures on the left and right are resonance structures for Carbon dioxide. However, they are very bad resonance structures and so they are usually not counted.
6.
Give the structure of CHFClBr. Which bond in this molecule would be the strongest bond? Which bond is most polar? Least polar?
The Carbon-Fluorine bond would be the most polar and strongest, the Carbon-Bromine bond would be the weakest bond in the molecules. Polarity and bond strength is based on the differences between electronegativity values for joined elements
7.
Which bond is strongest? HF, HCl, HBr, or HI? What kind of bond is between each of these atoms (nonpolar covalent, polar covalent, or ionic)?
HF—ionic (strongest) HCl—polar covalent; HBr—Polar covalent; HI—nonpolar covalent
(weakest)

8.
What molecule has the stronger bond, HCN or CO? Which molecule has the shortest bond between two atoms?
Nitrogen is a bigger atom than oxygen and so the carbon oxygen bond would be the shortest and strongest. *Remember periodic trends*