Question

What are the Lewis Structures for each of the following molecules? Show resonance structures, if they exist.

1.) O2
2.) N2
3.) CO
4.) SO2

Answer 1

O2 will have a double bond in order for each atom to have 8 electrons

(Each dash is a shared pair of electrons)

- = single bond
- - = double bond
- - - = triple bond

So O2: O - - O

N2 needs a triple bond, so it’ll be: N - - - N

CO: C - - - O

SO2: O - - S - - O

You can figure out how many bonds you need, using a method called “NASU”, which stands for: Needed Available Shared Unshared

For example, let’s use oxygen, O2

Needed Available Shared Unshared

O needs 8 it has 6 8-6=2 6-2=4
O needs 8. it has 6. 8-6=2. 6-2=4

Using this, we can see that each oxygen atom has 2 electrons to share and will be left with 4 unshared pairs.

To get the number of bonds, you’ll add the results under shared and divide by 2

So, 2+2=4, 4/2=2

O2 will have 2 covalent bonds. This checks out with the Lewis Structure I drew. ✔️