Formal Charge

Formal charge is the process of assigning electrons to a particular element in a compound (or ion).

To determine formal charge, you apply the following processes:

1. Assign half of all shared electron (those present in covalent bonds) to each of the elements that share those electrons.
2. Assign all lone pairs (or single electrons) on an atom to that particular atom.
3. Add together assigned shared electrons (half of those in any covalent bonds) to the number of electrons existing as lone pairs or single electrons.
4. Compare the total number of assigned electrons (from step #3 above) to the Group Number (Valence Number) of that element in the Periodic Table.

Now, to get Formal Charge, you must achieve one of the following:

• If the number of assigned electrons is equal to the Group Number, then Formal Charge is zero (0).
• If the number of assigned electrons is greater than the Group Number, the the Formal Charge is the difference between the assigned number of electrons and the Group Number (e.g., if assigned number of electrons is 5 and the atom is carbon with a Group Number of 4 (Group IV), then the Formal Charge would be -1, meaning it has one more electron than it should have assigned to it based on its Group Number).
• If the number of assigned electrons is less than the Group Number, the the Formal Charge is the difference between the Group Number and the number of assigned electrons (e.g., if assigned number of electrons is 4 and the atom is nitrogen with a Group Number of 5 (Group V), then the Formal Charge would be +1, meaning it has one less electron than it should have assigned to it based on its Group Number).