Final answer:
To determine the formal charges in the SN2 resonance structure, use the formula that equates formal charge to valence electrons minus lone pair electrons minus half the bonding electrons. This calculation shows that the formal charges for the nitrogen with the lone pair and sulfur are zero, while the nitrogen without the lone pair has a formal charge of +1.
Step-by-step explanation:
The formal charges of atoms in a molecule are computed by assuming that electrons in chemical bonds are shared equally between atoms and comparing the number of electrons around an atom in the molecule with the number of valence electrons that atom would have in its neutral state. To calculate the formal charge for each atom in the molecule or ion, use the formula:
Formal charge = (Valence electrons) - (Lone pair electrons) - ½(Bonding electrons)
Given the resonance structure of SN2 as described, with six electrons around sulfur (S) and two lone pair electrons on the terminal nitrogen (N), we would assign formal charges as follows:
- For Nitrogen with a lone pair: Formal charge = 5 - 2 - ½(6) = 0
- For Sulfur: Formal charge = 6 - 0 - ½(8) = 0
- For Nitrogen without a lone pair: Formal charge = 5 - 0 - ½(8) = +1 (assuming it shares a bond with another atom that accounts for 8 bonding electrons)
These formal charges should then be added to the resonance structure for accuracy and to facilitate the understanding of molecule reactivity and stability.