And in case you're still wondering how to draw carbon
monoxide,
The dative (ie. "donated") covalent bond is from oxygen to
carbon. Meaning, one lone pair from oxygen becomes a bond pair
between oxygen and carbon.
Your Kekule or dot-&-cross structure should show :
Carbon having 1 lone pair and 3 bond pairs.
Oxygen having 1 lone pair and 3 bond pairs.
Hence, carbon has a -ve formal charge, and oxygen has a +ve
formal charge.
This is due to the dative (ie. "donated") covalent electron bond
pair; oxygen has lost an electron, carbon has gained an
electron.
The reason why the dative bond occurs or exists, is to allow
both C and O to have a stable octet.
For physical chemistry (but not organic chemistry*), reflect the
nature of the dative bond with an arrow-headed line (as
opposed to a normal line for a normal or non-dative covalent bond),
for the Kekule structure.
For the dot-&-cross structure, the dative bond should be
represented as xx or oo (where x or o represent electrons from
oxygen), as opposed to xo or ox for a normal or non-dative covalent
bond.
(* In O.C., curved arrows represent electron flow mechanism. And
once the dative bond is formed, it is no different from any other
covalent bond. Hence in O.C., you only show the formation of the
dative bond using curved arrows; thereafter, normal lines to
represent the bonds.
In P.C., the arrow-headed line to represent the dative bond, is
actually the mechanism for the formation of the dative bond. If in
the exam, you're unsure which diagram to submit (ie. you're unsure
whether it's an O.C. or P.C. type question), do what the
intelligent exam candidate would do - draw both alternative answers
or forms, as long as both are correct, you'll get your marks.)