Chemistry I Honors – 12/11/07 Name ________________________________________________
Answers from yesterday: Drawing Lewis structures – the angles can be turned any way you want
for now… we’ll get into the angles later.
1. Br2
2. CH3Cl
3. SiF3Br
4. O2
5. N2
6. CO2
7. PCl3
P can have an exception to the octet rule – it can have 8 electrons, or it can have 6. You
cannot draw PCl3 with P having 8 electrons and get the number to come out correctly.
You have to use 6. Did you try to find out why this didn’t work???
8. N2O
Any of these could work… except #2. In #2, oxygen bonds 4 times. Oxygen has 6
valence electrons, so it can only bond twice. So, #2 is not valid. Also, if you put the
least electronegative element in the middle, #2 is out.
Drawing Ions
When you draw a Lewis structure of an ion, you should put brackets [ ] around the entire
structure, and then place the charge at the top right to indicate that the substance has a
charge. For instance, here is the nitrite ion, NO2 –
We won’t discuss resonance in Chemistry I. If you go on to AP Chemistry, we’ll discuss
what happens since you could draw this either way. For Chemistry I, either of these are
acceptable. The double bond can be on either side, take your pick. Notice how the
charge is clearly displayed though so you can tell it’s an ion and not a molecule!
This -1 charge means that the ion has accepted an electron. Therefore, it will have 1
more electron that it’s valence. If you add up 5 valence electrons for N, and 6 for each of
the O’s, you get 17 electrons. But there are 18 in the drawing! Where did the other
electron come from? The charge. So, when drawing ions be sure to include the charge.
Negative ions have gained electrons… so add those electrons to the valence electrons to
get the total number of electrons to work with.
Positive ions have lost electrons… so remove those electrons from the valence electrons
to get the total number of electrons to work with.
N
O
5X1= 5
6 X 2 = 12
5 + 12 = 17 + 1 electron from the charge = 18
Now you try drawing some ions:
1. Nitrate
2. Sulfate
3. Carbonate
4. Hydroxide
5. Sulfite
6. Acetate
7. Phosphate
8. Oxalate
9. Ammonium
10. Chlorite