Arkansas State University Department of Chemistry and Physics

Lewis Dot works best for covalent compounds of group A elements, though Lewis Dot Structures can explain electron transfer in ionic compounds.  By following the rules below, the Lewis Dot Structure can be written for covalent compounds and some polyatomic ions.

 1.  Count the total number of valence electrons, adjust for charge if an ion.  Add one electron for each negative charge, subtract one electron for each positive charge.

 2.  Place a pair of electrons between the central atom (usually written first) and each of the outer atoms.

 3.  Complete the octet of the outer atoms (except H, which needs only 2 electrons).

 4.  Place extra electrons, if any, on the central atom in pairs.

 5.  If the central atom does not have a complete octet, share extra electrons from the outer atoms until the central atom and the outer atoms have a complete octet.  Note: halides do not form double bonds.