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Why does the most stable structure for carbon monoxide have a triple bond between carbon and oxygen and 1 lone pair on each? I thought it would be a double bond between carbon and oxygen with one lone pair on carbon and one lone pair on oxygen because this gave me a formal charge of 0 on both carbon and oxygen. With triple bonds I got formal charges of 1 on carbon and -1 on oxygen.
With a double bond and one lone pair on each atom, you do not form a full octet because there's only 6 electrons on carbon and oxygen. In order to get full octets and an overall neutral charge you must use the triple bond and a lone pair on each.
C and O have a combined total of 10 valence electrons available for bonding. This means that there must be a triple bond with two lone pairs on each atom to satisfy the octet rule, with each atom having 8 electrons. Having only a double bond would means there wouldn't be enough electrons to satisfy the octet rule, and the atoms would have less than 8 electrons each. As such, they must share electrons. This is the only possible structure, so while it would be best to have 0 formal charge on all the atoms, it is not possible for this structure due to the number of electrons.
Carbon Monoxide has a total of 10 valence electrons. Carbon having four and Oxygen having six they combine to have 10 total valence electrons. If the carbon and oxygen were double bonded (4 shared electrons), and each had a single pair then you would only have a total of 8 valence electrons. 1 lone pair plus 1 lone pair equals 4 valence electrons. You would therefore dissatisfy the octet rule for both atoms as both would only have 6 valence electrons.
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