Lesson 3-8

Lewis Dot Diagrams

     Electron dot diagrams, which are also called Lewis dot diagrams, are very useful tools in Chemistry.  They will give you the ability to determine the type(s) of covalent bonds that an element may make in certain situations.  They can also be used to predict the type of ion that an atom might make when it forms an ion.  Each dot diagram consists of; an elemental symbol, which represents the kernel of the atom, and a group of 1-8 dots which shows the configuration of the outer-most electron shell of the atom, also called the valence shell.

     Below is an example of the proper Lewis dot diagram for the element oxygen. 

    The "O" in the example above represents the kernel of the atom, that is the nucleus and all of the electrons, except those in the valance (outer) shell.  Each of the four "sides" of the symbol represents an orbital in the outermost energy level of the atom.  Since each orbital can hold only two electrons, the sides of the dot diagram can only hold up to two dots.   The six dots show the configuration of the of the valence electrons. 

     To make a Lewis dot diagram, you need to know how many electrons are in the valence shell.  If you don't know off hand, you would start by writing the electron configuration.  You should remember that the electron configuration of oxygen is 1s² 2s² 2p⁴.   The six electrons shown on the dot diagram are those in the second principle energy level.    You fill in one valence electron on each side of the elemental symbol, and then double up as many sides as you need to in order to include each one.   Remember that each side can only hold up to two dots!

     Below you will see an example of the order of filling in the dots on a dot diagram for an element with eight valence electrons.   Please note that you can place the first two dots on any side, but the rest of the dots should be placed in either a clockwise or counter clockwise manner, with no side receiving two dots until each side gets one.

Step One	Step Two	Step Three	Step Four
Step Five	Step Six	Step Seven	Step Eight

     By looking at the electron dot diagram for oxygen we can see that oxygen has two unpaired electrons, so it has two electrons available for standard covalent bonds.

           These unpaired electrons might make two single covalent bonds, as is the case in water (H₂O).  Or, they might make one double covalent bond, as the case of magnesium oxide (MgO).  When Lewis dot diagrams are used for compounds, "x's" are often used to substitute for the dots of one or more elements in order to show which electrons came from which element. 

     Let us look at the Lewis dot diagrams for both oxygen and hydrogen as free elements, and then at water as a compound.

    Now we will show electron configurations and the dot diagrams for a few more elements.  Remember that the dots represent the electrons that are found in the valence shell, or energy level with the highest value for n (principle quantum number).  For these examples, I will color the valence shell of each element black.

     Now try some examples on your own, using the worksheets found below.

Please forward all questions, comments and criticisms to Gregory L. Curran.
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Last Modified February 07, 2008