The other oxide of carbon is carbon monoxide, CO. It results from incomplete combustion of carbon or its compounds, when insufficient oxygen is present. It is isoelectronic with the molecule; if by some magic we could pluck a proton out of the oxygen nucleus in CO and give it to the carbon, would be the result. Like , CO has a triple bond between atoms and one lone pair on each atom:



The electron pair for the third bond in CO must be provided entirely by the O atom, since it has six electrons in its outer shell, whereas C has only four.