In the case of hemoglobin, because the carbon monoxide binds very strongly to the iron, the CO blocks the position where oxygen would normally be bound and carbon monoxide poisoning results. They tell us if one atom is donating extra electrons to another to give it an octet.
If an atom needs to donate more electrons than normal in order for everyone to get an octet, it will have a positive formal charge.
Carbon has a normal valence of four, and it has four bonds here. There are no formal charges on the hydrogens either.
Carbon monoxide has a structure that is very similar to formaldehyde. With ten electrons total, the only way to get an octet on both atoms is to make three bonds between carbon and oxygen.
In a particular structure, Formal charge of an atom is the difference between its Valence electrons & the number of electrons assigned to that atom in a particular Lewis structure.
Number of e's assigned is half of the no of bonds formed by the atom plus electrons in the lone pair.New chemical bonds are formed by sharing electrons.Old chemical bonds are broken when one atom takes the bonding electrons away from another atom.A long, annoying trip to my professor’s office hours enabled me to figure it out, but it was still overwhelmingly TEDIOUS!In chemistry, a formal charge (FC) is the charge assigned to an atom in a molecule, assuming that electrons in all chemical bonds are shared equally between atoms, regardless of relative electronegativity.These charges cancel to give an overall neutral molecule.What we are really doing when we assign formal charge is comparing how many electrons the atom brought with it from the periodic table to how many it has now.It is done simply to determine whether the atom has a noble gas configuration right now.Electron counting to determine formal charge is done to keep track of who has given electrons to whom when making the molecule.When determining the best Lewis structure (or predominant resonance structure) for a molecule, the structure is chosen such that the formal charge on each of the atoms is as close to zero as possible.The formal charge of any atom in a molecule can be calculated by the following equation: where V is the number of valence electrons of the neutral atom in isolation (in its ground state); N is the number of non-bonding valence electrons on this atom in the molecule; and B is the total number of electrons shared in bonds with other atoms in the molecule.