Mr. Sklar's Whiteboard

When working with charged molecules, or molecules with no overall charge but individual elements are charged, the earlier method of drawing Lewis structures will not work. These structures must be drawn utilizing the following rules:

  1) Count the number of valence electrons.

  2) Draw a skeleton structure only using single bonds between elements.

  3) Fill in all the elements octets with the required number of dots.

  4) If you have too many electrons, eliminate electrons by putting double bonds between atoms. Each new bond adds two electrons to the structure, but eliminates four electrons from the atoms the bond has formed between.

  5) Find the formal charge on each individual atom by comparing the number of valence electrons it has to the number that it should have. Indicate individual charges by writing the charge next to the atom and putting it in a circle.

  6) If the molecule has an overall charge, place square brackets around the structure and write the overall charge outside the brackets in the upper right hand corner.

                    Click on an example:        C₂O₄^2-        CH₆N⁺        SO₂        POCl₃