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Example 7.6: Calculating Formal Charge from Lewis Structures

Assign formal charges to each atom in the interhalogen ion \(\ce{ICl4-}\).

Solution

We divide the bonding electron pairs equally for all I–Cl bonds:

We assign lone pairs of electrons to their atoms. Each Cl atom now has seven electrons assigned to it, and the I atom has eight.
Subtract this number from the number of valence electrons for the neutral atom:

\(\mathrm{FC}_{\mathrm{\ce{I}}}\) \(= 7 - 8\)

\(\ \ \ =-1\)


\(\mathrm{FC}_{\mathrm{\ce{Cl}}}\) \(= 7 - 7\)

\(\ \ \ =0\)


The sum of the formal charges of all the atoms equals -1, which is identical to the charge of the ion (-1).