Arrange the other atoms around the central atom, in accord with the normal valences of the atoms. That is, do not place more atoms around a central one than it normally can bond to.
Hydrogen never is the central atom. It forms only one bond, so it must generally be in the outer layer of atoms. Therefore, place hydrogen atoms last.
By application of Rules 4 and 5, the structures of our examples become:
In either case, move an unshared pair from a peripheral atom to make a double bond to the central atom. If the central atom still has too few electrons, move another pair from the same atom to make a triple bond, or a pair from another atom to make a second double bond.
When this action can be taken in more than one way, write all possible ways as separate structures. You have discovered resonance; the actual structure is a hybrid of all of the individual structures.
Our two remaining example structures thus become:
formal charge = (number of valence electrons on the neutral, uncombined atom) - (number of covalent bonds to the atom in the current structure) - (the number of unshared electrons [not pairs] on the atom in the current structure)
For example, for the O in POCl3, we have:
Thanks to Professor Emeritus John Gordon, Kent State University, and Dr. Joyce Brockwell, Northwestern University, friends and former colleagues, for the original version of these Rules.