The Lewis structure for the chlorate ion is

Calculate the formal charge on the chlorine (Cl) atom. Express your answer as an integer.

For certain molecules such as CS_{2}, there is more than one isomer possible. For each isomer, a Lewis structure can be drawn and the formal charge on each atom can be calculated. You can use the formal charges to determine the most stable structure for a molecule. As a rule, the Lewis structure with the lowest formal charge on each atom and which places the negative charge on the most electronegative atom is generally the most stable structure.

The formal charge on an atom is calculated using the following formula:

$\mathbf{formal}\mathbf{}\mathbf{charge}\mathbf{}\mathbf{=}\mathbf{}\mathbf{(}\mathbf{number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{valence}\mathbf{}{\mathbf{e}}^{\mathbf{-}}\mathbf{)}\mathbf{}\mathbf{-}\mathbf{}\mathbf{\left[}\mathbf{\right(}\mathbf{number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{non}\mathbf{-}\mathbf{bonding}\mathbf{}{\mathbf{e}}^{\mathbf{-}}\mathbf{)}\mathbf{}\mathbf{+}\mathbf{}\mathbf{(}\frac{\mathbf{1}}{\mathbf{2}}\mathbf{}\mathbf{\times}\mathbf{}\mathbf{number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{bonding}\mathbf{}{\mathbf{e}}^{\mathbf{-}}\mathbf{\left)}\mathbf{\right]}$

CS_{2} as shown in the interactive activity has two isomers. In one structure carbon is the central atom, and in the other sulfur is the central atom. In the first structure, the formal charges on the S, C, and S atoms are 0, 0, and 0, respectively. In the second structure, the formal charges on the C, S, and S atoms are − 2, +2, and 0 respectively. In the second structure, it is not possible to create a resonance structure that has formal charges of zero on each atom. It is unlikely that sulfur is the central atom in this molecule.

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