Lewis Structures: Simple Organic Compounds

November 30, 2012

Video by Janet Gray Coonce, MS

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C₂H₄ is the symbol for the simple organic compound, ethylene. It is the simplest alkene (hydrocarbon with carbon-carbon double bonds). This illustration demonstrates how to draw the Lewis dot structure for C₂H₄.

The first step is to write the symbols for carbon (C) adjacent to each other in the center and the hydrogens (H) will have to surround the carbons. The hydrogen atoms will be distributed evenly on the outside of the molecule so we draw 2 symbols for H outside each carbon. The next step is to draw the valence electrons. Hydrogen has 1 carbon has 4.

In this diagram, the dots were connected to show that the valence electrons are being shared in covalent bonds. Each of the lines represent 2 electrons being shared. Remember that hydrogen needs 2 valence electrons (a duet) to complete it’s outer shell. Carbon needs 8 valence electrons (an octet) to complete its outer shell. As we look over this diagram, we can see that by sharing in covalent bonds, every atom has a full outer shell of valence electrons (2 around each hydrogen and 8 around each carbon).

C₂H₂ is the symbol for the simple organic compound, acetylene. It is the simplest alkyne (hydrocarbon with carbon-carbon triple bonds). This illustration demonstrates how to draw the Lewis dot structure for C₂H₂.

To begin, a C for each central carbon was drawn in the center. The hydrogens must go on the outside and they must be as far apart from each other as possible, so we draw one on each side of the molecule in line with the carbon atoms. Next we put in a dot for each electron and connect the dots.

CH₂O is the symbol for the simple organic compound, formaldehyde. It is the simplest aldehyde (hydrocarbon with a carbon atom connected to an oxygen atom by a double bond and to a hydrogen atom by a single bond). This illustration demonstrates how to draw the Lewis dot structure for CH₂O.

On the left the attempt to draw the Lewis structure failed when we attempted to join one of the hydrogens to oxygen. However, on the right, we know it is the correct Lewis structure because all atoms have their complete set of valence electrons. There are 8 surrounding oxygen and carbon (a complete octet) and hydrogen has its full set of 2 (duet).

Solutions to problems: