Question

If the net charge on a molecule is zero, must the formal charge on every atom in the molecule equal zero? Why or why not?

Short answer

No, the net charge on a molecule being zero does not mandate that the formal charge on every atom within the molecule is also zero. The charges may cancel out to result in a neutral molecule, but individual atoms can possess a nonzero formal charge.

Step-by-step solution

Understand Net Charge

Net charge is the sum of the positive and negative charges in a molecule. If the molecule is neutral, the net charge would be zero, indicating that there are an equal amount of positive and negative charges.

Understand Formal Charge

Formal charge is the charge assigned to an atom in a molecule, assuming that electrons in all chemical bonds are shared equally between atoms, regardless of the relative electronegativity of the atoms. It is calculated for an atom in a molecule as the number of valence electrons in the free atom minus the number of valence electrons assigned to the atom in the molecule.

Establish the Relationship

The key thing to note here is that while the net charge on a molecule may be zero, this does not necessarily mean that the formal charge on every atom within the molecule is also zero. The formal charges on the atoms could cancel each other out, yielding a zero net charge for the entire molecule while the individual atoms have formal charges which are nonzero.