Chemistry / Unit 6 Chem 0991 worked example, 60 to 90 seconds
Drawing a Lewis Structure
The idea
Drawing a molecule's Lewis structure means arranging its atoms around a central atom, connecting each with a single bond, distributing remaining valence electrons as lone pairs to complete outer octets, then converting lone pairs to additional bonds if the central atom still lacks an octet.
In practice
For carbon dioxide, CO2, carbon is placed centrally with an oxygen on each side, each linked by a single bond. Distributing the remaining electrons as lone pairs first fills both oxygens' octets, leaving carbon with only four electrons around it. Converting one lone pair from each oxygen into a second bond gives carbon two double bonds, completing an octet on every atom while using all sixteen of the molecule's valence electrons.
Where people slip
Stopping after single bonds and lone pairs, without converting pairs to additional bonds when a central atom's octet is still incomplete, is the single most common Lewis-structure error and produces a carbon with only four electrons.
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