# Determine polarity of covalent bond with formal charge

In a covalent molecule, can we conclude that if the formal charge between two atoms are +1 and -1 respectively, then the chemical bond acting between them is a polar covalent bond (such as the bond between N and single-bonded O in Nitrate Ion)? On the other hand, if both of the atoms has a formal charge of 0, then the chemical bond acting between them is a nonpolar covalent bond (bonds in sulfur dioxide and sulfur trioxide)? How about bond between atoms with formal charge of +1 and 0 (P with single-bonded O in phosphate ion)?

Check out these structures of nitric acid, sulphur trioxide and carbon monoxide. (Resonance structures applicable to $\ce{HNO3}$ and $\ce{SO3}$ not displayed.) All bonds are polarised towards the oxygen, since oxygen’s electronegativity is $3.5$; the second highest amoung the non-noble-gas elements. Note especially that the bonds in $\ce{CO}$ are polarised towards oxygen despite oxygen bearing a formal positive charge. (There is a lot more to $\ce{CO}$ which is shown well in Martin’s answer including the molecular orbitals)