3. Formal charge

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What is formal charge?

The charge on an atom in a Lewis structure, assuming all bonding electrons are shared equally between atoms

how do you calculate formal charge?

Valence electrons - unshared electrons - ½ bonding electrons

How do you know if you calculated formal charges properly?

If compound is neutral, FC must equal zero/ FC must equal the charge on an ion

How do we find the best Lewis structure (lowest energy structure) using FC? Part 1

1) A structure with FC closest to zero; if a charge exists, it should be as small as possible (ex +1 is better than +2)

How do we find the best Lewis structure (lowest energy structure) using FC? Part 2

If formal charges cannot be avoided for a molecule, then negative charges are favored on the MOST electronegative elements.

How do we find the best Lewis structure (lowest energy structure) using FC? Part 3

Check for resonance (multiple stabilization structures)