instances

A formal fee (FC) is the fee assigned come an atom in a molecule, assuming the electrons in all gaianation.netical bond are mutual equally between atoms, regardless of loved one electronegativity. When determining the finest Lewis structure (or primary resonance structure) for a molecule, the framework is preferred such the the formal charge on every of the atoms is as close come zero together possible.

You are watching: What is formal charge used for

The formal charge of any type of atom in a molecule have the right to be calculate by the following equation:

where V is the variety of valence electrons of the neutral atom in isolation (in its floor state); N is the number of non-bonding valence electrons on this atom in the molecule; and also B is the total variety of electrons common in bonds with other atoms in the molecule.


Examples

Example: CO2 is a neutral molecule v 16 total valence electrons. There are three various ways to draw the Lewis structure Carbon single bonded to both oxygen atoms (carbon = +2, oxygens = −1 each, complete formal fee = 0) Carbon single bonded to one oxygen and dual bonded to another (carbon = +1, oxygendouble = 0, oxygensingle = −1, full formal charge = 0) Carbon double bonded come both oxygen atoms (carbon = 0, oxygens = 0, complete formal fee = 0)

Even despite all 3 structures gave us a full charge that zero, the final structure is the premium one because there room no fees in the molecule in ~ all.


Alternative Method

The following is equivalent:

attract a circle about the atom for which the formal fee is requested (as through carbon dioxide, below)

*

counting up the variety of electrons in the atom"s "circle." since the circle cut the covalent bond "in half," each covalent shortcut counts together one electron instead of two. Subtract the number of electrons in the circle from the group number of the element (the Roman numeral from the older system of team numbering, not the IUPAC 1-18 system) to recognize the official charge.

See more: Who Is Still Alive From Dukes Of Hazzard, 'Dukes Of Hazzard' Actor Dies At Age 96

*

The official charges computed for the continuing to be atoms in this Lewis framework of carbon dioxide are shown below.

*
api/deki/files/123993/350px-Co2comp.png?revision=1" />

The reason for the difference in between these worths is that formal charges and also oxidation states stand for fundamentally different ways of looking at the circulation of electrons among the atom in the molecule. With formal charge, the electron in each covalent bond space assumed to be break-up exactly evenly in between the 2 atoms in the link (hence the separating by two in the method described above). The officially charge check out of the CO2 molecule is essentially displayed below:

*

The covalent (sharing) aspect of the bonding is overemphasized in the usage of official charges, since in truth there is a higher electron density approximately the oxygen atoms because of their greater electronegativity compared to the carbon atom. This can be most properly visualized in one electrostatic potential map.

With the oxidation state formalism, the electron in the bonds space "awarded" to the atom through the greater electronegativity. The oxidation state see of the CO2 molecule is displayed below: