Untitled - Kelly Walsh High School

138 CHEMISTRY FOR THE UTTERLY CONFUSED
Quick Tip
Quick Tip
to each other unless there is no alternative. This is an oxyacid. The hydrogen is
acidic. When you arrange the atoms for an oxyacid, the acidic hydrogens will
always attach to an oxygen atom. This oxygen atom will have only one hydrogen
atom attached. This oxygen will also attach to the other element in the compound.
If there is more than one acidic hydrogen atom, attach one to a separate
oxygen atom. The resultant order of atoms that you get might be HONO. It
does not matter to which oxygen you attach the hydrogen atom. The arrangement
ONOH is the same as HONO. You may arrange these atoms in a horizontal
arrangement as done here, or a vertical arrangement, or . . . . It makes no
difference. We will use the first arrangement in this example.
When you begin a Lewis structure, do not place identical atoms adjacent to each
other unless there is no alternative. Carbon is the only common exception. Most
compounds containing more than one carbon atom will have the carbon atoms
adjacent to each other.
When drawing the Lewis structure of an oxyacid, you should place one acidic
hydrogen atom on a separate oxygen atom.
We know that there needs to be at least one bond between each pair of atoms.
We also know that the bond from hydrogen to the adjacent oxygen will be the
only bond to the hydrogen atom. This information should be on your mind as
you move on to complete the structure.
If you wish to apply the S N A rule, you will need to assign values to N and
A. To find N, we use 2 for hydrogen and 8 for each of the other three atoms. This
gives N 2 3(8) 26. The determination of A uses 1 for hydrogen, 5 for nitrogen,
and 6 for each oxygen atom. This gives A 1 5 2(6) 18. Using the
values for N and A, we find S 26 18 8. If S 8, then there are S/2
4 bonds. We can place one bond between each pair of atoms to get H-O-N-O.
This arrangement accounts for three of the four bonds. Since there is one more
bond to account for, we need to create a double bond. The double bond cannot