FAQS

Lewis dot structures are simplified drawings of how valence electrons are arranged around atoms in a molecule. They also illustrate bonds between elements in a molecule.

Lewis dot structures use the "Octet Rule."  The octet rule states that atoms gain, lose, or share electrons on the atom's outer shell. With a few exceptions (Hydrogen only "likes" two electrons), most atoms like to have eight electrons on the outer shell and will bond with other atoms to achieve that number of electrons.

Follow these steps to create a lewis dot structure for a molecule:

1. Use the Periodic Table to determine the total number of valence electrons in a molecule.

Note: Numbers in red have been added to the columns in the Periodic Table below to indicate the number of valence electrons elements in that column have.

Example: H2O      H=1 + H=1 + O=6  equals 8 valence electrons

2. Apply the "octet rule."  Atoms are "happy" when they have 8 electrons in their outer shell.  Draw a lewis dot structure for each element in the molecule by writing the letter for the element and placing the electron(s) around the letter, one or two electrons on each side. (Imagine a square around the letter and place dots on the sides of the square.)

3. Choose which atom will be in the center. In this example, Oxygen has the most electrons so will appear in the middle. The hydrogen atoms will appear on either side.

4. Determine covalent bonds. The octet rule states that atoms like having eight electrons. A bond forms when two atoms share electrons. Using the example, Oxygen needs two more electrons to achieve the octet rule.  Hydrogen can bond to Oxygen by sharing electrons. Also, Hydrogen "likes" having two electrons. A covalent bond is illustrated with a straight line. This line represents two electrons shared between atoms.

The lewis dot structure is complete! In this illustration, the octet rule is satisfied (Oxygen now has 8 electrons in its outer shell) and the Hydrogen atoms each share an electron with oxygen by forming covalent bonds.  This gives Hydrogen the preferred two electrons.

For more information on lewis dot structures, see:

Renneboog, R. M. (2020). Lewis structure and diagram. Salem Press Encyclopedia of Science.

Lewis electron dot structures. (2011). In L. D. Williams, Chemistry DeMYSTiFieD (2nd ed.). McGraw-Hill.