Formal Charge

[salvadorramos3k]

When is it necessary to calculate the formal charge? Is it just to see if something is an ion? Or what exactly is the purpose of calculating the formal charge?

[Jamie Lee 1H]

You want to calculate formal charge when figuring out the lowest energy lewis structure because this means having the most stable structure. The lower the formal charge for the molecule, the more stable a molecule is.

[JinwooLee_1F]

You should calculate formal charge when you are drawing lewis structures and have more than one possible structure. The one with the lowest formal charge is the most favorable, as it is the most stable structure.

[Noah Canio 3C]

Like everyone above mentioned, formal charge should be calculated always when drawing Lewis structures. However, when drawing the "best" structure or the one with the lowest energy, it's important to note that you should calculate formal charge only after:

1.) Making sure your structure contains the same amount of electrons present within the species/compound/molecule you're given
2.) Making sure your structure adheres to the octet rule. (Remember, there are many exceptions to this. The first four elements and Boron's entire column can have fewer electrons. In addition, radicals will have less because of having an odd # of electrons. Also, any element beyond the third period will be able to have an expanded octet).

Only after going through what's above should you calculate formal charge to make sure you have the right Lewis structure.

[KHowe_1D]

You want to calculate the formal charge to ensure that you have the most stable molecule.

[Isabella Dal Porto 1H]

Calculating the formal charge allows you to find the most stable structure. Thus, just follow the equation FC = # Valence electrons - (# Lone pair electrons + # Shared electrons/2).