Lewi Structures: Carbon dioxide and Methanol

Video by Janet Gray Coonce, MS

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How do we use Lewis dot structures to illustrate bonding in CO₂?  We we know that the oxygen atoms will repel each other so carbon will be in the center with an oxygen at each end.  How many valence electrons do each of those atoms have?  Well we know oxygen has six valence electrons because it is in periodic table group 6A.  Carbon is in group 4A of the periodic table so it has 4 valence electrons.

This Lewis dot structure demonstrates that oxygen has 2 unpaired electrons and has 2 unpaired electrons available for covalent bonds. Carbon has 4 unpaired electrons available for 4 covalent bonds.

The illustration shows how to use a Lewis dot structure to represent the bonding in the CO₂ molecule.

Lewis Dot Structure for Methanol

The chemical symbol for methanol is CH₃0H or CH₄0.  Hydrogen can only form one bond so it can not be the central atom.  Hydrogen is always on the outside of a molecule with which it is sharing electrons.  We know therefore that Carbon and Oxygen will be in the center with 3 hydrogen atoms surrounding the carbon atom and a single hydrogen bonding the oxygen atom.

Here we demonstrate the valence electrons with dots.  Carbon has 4, hydrogen 1 and oxygen 6.  It is easy to see that when the electrons are shared each atom will have its outer shell completed.  With sharing each hydrogen will have 2 electrons, carbon 8 electrons and oxygen 8 electrons in the outer shell.  The molecule is balanced and happy .   

When the dots are connected between the shared electrons, the Lewis dot structure is completed.  This is the Lewis dot structure for methanol. 

Transcription by James C. Gray MD FACOG