LEWIS DOT STRUCTURES FOR COVALENT COMPOUNDS



1. Count the dots: That is, sum up the number of dots each atom has (equal to the Roman numeral on top of the column the atom is found on the periodic table.)


If an ion has a negative charge. Add additional "electrons" to your count equal to the negative charge.
If an ion has a positive charge, subtract "electrons (dots)" from your count


2. Make a Pretty Picture: That is, arrange your atoms on the paper in some esthetically pleasing way. Usually with the "LEAST" electronegative atom in the middle surrounded by the "more" electronegative atoms. (Hint, H and F are always on the outside of your molecule.)


3. Draw a Line Between the Atoms: Draw a line (which represents and uses two dots from your total above) between the central atom and each of the outside atoms. This forms a bond that keeps those outside atoms stuck to the central atom (necessary if the thing you are drawing is a molecule).


4. Satisfy the Octet of the Outside Atoms First: Start putting your dots back on your molecule, satisfying the outside atomsí "octet rule" first. That is, put 6 more dots around each outside atom (making a total of 8 dots if you count the attaching line). Remember H only has one line and no more dots. (Its octet is only 2). Also remember each line you added earlier used two dots.


5. If You Have Any Extra Dots, Put Them in the Middle: If you have extra dots after you have went around satisfying the octets of all the outside atoms, place the extras on the central atom. (Do this even if you violate the octet rule of the central atom).


6. If You Are Still Missing Dots in the Middle, Move a Lone Pair "In": If after you go around the outside and you placed any extra electrons on the central atom OR when you have run out of electrons, it may be that the central atom is still "unhappy". That is, there are still insufficient electrons to satisfy the octet of the central atom. If that happens, then move a lone pair of electrons in from an outside atom to form a double or triple bond between the central atom and the atom you moved the electron pair from.


It may happen that the central atom is STILL unhappy after rule 6 above and needs more electrons. Then do it again! Move ANOTHER lone pair in from an outside atom in to form yet another multiple bond.

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If your substance was an ion, do not forget to put brackets around the molecule and indicate the electrical charge on the species in the upper right corner.