why does CO has a triple bond not a double bond?

Question

why is carbon monoxide C (1 lone pair) triple bond O (1 lone pair)
but not C(1 lone pair) double bond O (2 lone pairs)
because the formal charge for the triple bond comes out to, 4 - 5 = -1
and 6-5 = 1
yet the double bond comes out to 0 and 0...
isn't a 0 formal charge arrangement preferred?

Answer 1

Well, you are missing an important detail, that CO with a double bond doesn't satisfy the octet rule on C. Carbon is one of those elements that will almost never be stable without an exact octet. With a triple bond, you can satisfy the octet rule on both C and O, even though there are nonzero formal charges. So CO behaves as though it has a triple bond.

Answer 2

Co Triple Bond

Answer 3

I can certainly see why a triple bond is formed using simple molecular orbital diagrams. Though it is clear that a triple bond adds octet stability, and a double bond gives formal charge stability, I find it curious that the octet stability of carbon is enough to overcome the large electronegativity difference between the species. For carbon to create a coordinate covalent bond with oxygen and obtain a -1 formal charge seems unlikely yet what apparently occurs. Though I have seen CO for years with a triple bond, only this year when teaching it did the formal charge improbability jump out at me. Anyone have other thoughts on what allows this to occur?

Answer 4

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CO has three resonance structures but the one which contributes the most is the one with the triple bond. Both the carbon and the oxygen have a lone pair. The other two resonance structures are: - Carbon with one lone pair double bonded to oxygen with two lone pairs. - Carbon with one lone pair single bonded to oxygen with three lone pairs.