Refresher: Each atom on the periodic table has a set number of valence electrons. The number of valence electrons increases across the periodic table. When atoms form covalent bonds, one pair of electrons is shared between the atoms for every single bond. Two pairs of electrons are shared in a double bond and three pairs are shared in a triple bond.
Formal charge is the charge placed on each atom in a molecule, ignoring relative electronegativities. It is a result of the electrons associated with each atom in the molecule. Even if a molecule is overall neutral, a formal charge can be associated with the atoms in the molecule (which would add up to result in an overall zero charge). Knowing how electrons are distributed in a molecule and the formal charge helps us to predict how the molecule will react.
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