How to Do a Lewis Dot Diagram of Ions

Learn to draw Lewis dot structures for ions.

Lewis dot diagrams of atoms and ions aid chemists in the determination of which atoms are bound to each other on a simplistic scale. Atoms are most stable when they have enough electrons to fill the valance shell of their electronic structure. Ions are nothing more than atoms with one or more electrons missing from the valance shell. The valance shell of an atom is complete when eight electrons fill the shell. The filling of the valance shell leaves the atom in the same electronic configuration as the noble gas atoms. The electron shells around the atom have specific maximum numbers of electrons that can reside in them. The shell identified as the valence shell is the shell for the "p orbitals."

Instructions

1. Select the atom of interest and populate the valance shell of the neutral atoms. Draw the four orbitals along the four sides of the element's symbol, one on top and bottom and one on each side. Each of the four sides can hold two electrons. For example, the following list of atoms is coupled with the number of electrons in their valence shell: Ar -- 8, Cl -- 7, Na -- 1, C -- 4. Each electron in a valance shell resides in an otherwise empty position unless none is available. For one to four valance electrons, the electron enters one of the four empty positions. The fifth valance electron must enter a position that already contains a valance electron.

2. Determine the number of electrons you must add or remove from the atom to create the ion of interest. For example, determine the number of electrons you must add or remove to create the following ions: Na+, Cl-, Mg+2 and O-2. Na has one lone electron in the valance shell so it can lose one electron to create Na+. Cl- has seven electrons in the valance shell and requires one more electron to achieve the stable noble gas electron configuration with the valance shell completely filled. Mg+2 can lose the two electrons that it has in the valance shell allowing it to have the noble gas configuration of electrons. O-2 requires two more electrons to add to its own six electrons to fill the valance shell.

3. Add or remove the required number of electrons from the base configuration of the neutral atom. When adding or removing electrons, place or remove the new electrons symmetrically. Fill the four orbitals by filling one electron in each orbital before adding a second electron to any of the orbitals.

References

• Process Oriented Guided Inquiry Learning: Lewis Dot Structures of Atoms and Ions
• Aus-e-Tute: Lewis Structures (Electron Dot Diagrams)