How do you determine if a molecule has a polar covalent bond based on the lewis dot structure?
When you draw the lewis dot structure can you draw a circle around both atoms that represent a stable inert gas structure.
In a covalent bond the electrons are shared between both atoms, in a roughly equal manner. If the electron structures for both atoms are stable after sharing they will share the electrons covalently.
: O :: C :: O :
If you draw a circle around either Oxygen it will have 8 electrons a stable structure. The four electrons from the double bond and the four electrons from the two pairs of unshared electrons on the Oxygen.
If you draw a circle around the Carbon it will have 8 electrons a stable structure. The two sets of four electrons from the double bonds joining the Carbon to the two Oxygens.
If you draw a circle around the Sodium it has only 2 electrons which is not a stable structure. The Sodium will lose the 2 electrons that form the bond with Chlorine. The losing rather than sharing the electrons creates an ionic bond.
You calculate the electronegativity differences (
For example, the Lewis structure of
Look up the electronegativities of
This value is greater than 0.5, so the
Now consider the Lewis structure for
The electronegativities are
This is about as nonpolar as you can get for a bond between two different atoms.