Formal Charge Calculation

[Baoying Li 1B]

Hey guys, can someone explain the process of assigning formal charges in detail? What is it mean to count the bonding? Why is the resonance the most stable when Fc equals to 0?

[Camellia Liu 1J]

Formal charge indicates the gain or the loss of electrons of an atom in the formation of a covalent bond.

To assign formal charge:
Formal Charge = V - (L + ½ S)
where V is the number of valence electrons in the free atom
L is the number of electrons present on the bonded atom as lone pairs
and S is the number of bonding/ shared electrons on the atom

When there is a low formal charge, it means that an atom has undergone only a small redistribution of electrons relative to the free atom

[LNgo 1G]

The resonance form with the most formal charges equal to zero means that there is a more equal sharing of electrons since there are no partial charges on the atom(s).

[Micah3J]

When calculating the formal charge, we want the outer elements to carry the negative charge as opposed to the middle element right? If so, can someone explain why?

[Chantel_2I]

When calculating the formal charge, we want the outer elements to carry the negative charge as opposed to the middle element right? If so, can someone explain why?

The element with the lowest ionization energy goes in the middle, which means the middle one is less electronegative than the outer ones. Since the outer atoms are more electronegative, they would be more stable with a negative charge than the middle atom would be because they more strongly attract electrons.