Question

what is the formal charge on the cl atom in the perchlorate ion, clo4-, shown below?

Explanation:

Step1: Recall formal - charge formula

The formula for formal charge is $FC = V - N - \frac{B}{2}$, where $V$ is the number of valence electrons, $N$ is the number of non - bonding electrons, and $B$ is the number of bonding electrons.

Step2: Identify values for chlorine in $ClO_4^-$

Chlorine (Cl) has 7 valence electrons ($V = 7$). In the perchlorate ion, Cl has 0 non - bonding electrons ($N = 0$) and 8 bonding electrons ($B = 8$) since it is double - bonded to 4 oxygen atoms.

Step3: Calculate formal charge

$FC=7 - 0-\frac{8}{2}=7 - 4= + 3$. But we can also consider the overall charge of the $ClO_4^-$ ion. Another way is to note that the sum of formal charges of all atoms in an ion equals the charge of the ion. Oxygen has a formal charge of 0 in this structure (since for each $O$: $V = 6$, $N = 4$, $B = 4$, $FC = 6 - 4-\frac{4}{2}=0$). The overall charge of $ClO_4^-$ is - 1. Let the formal charge of Cl be $x$. Then $x+4\times0=-1$, so $x = + 3-4=-1$.

Answer:

• 1