Using the rules to determine Lewis Dot Structures, there are some compounds or ions that could have more than one viable Lewis Dot Structure (not talking about Resonance structures.
It usually occurs when you have elements that can exceed the Octet Rule and are the central atom.
There can not be two viable Lewis Dot Structure for a compound/ion, therefore there must be a way to determine which structure is more correct. There is and it is called FORMAL CHARGE.
Formal charge - the difference between the number of valence electrons on free atom and number of valence electrons assigned to the atom in a molecule (valence e- shared - valence assigned)