To determine the formal charges on chlorine (Cl) and oxygen (O) in the perchlorate ion (ClO4–), we need to follow a few steps involving the calculation of formal charge.
The formal charge (FC) can be calculated using the formula:
FC = V – (N + B/2)
- V = number of valence electrons in the neutral atom
- N = number of non-bonding (lone pair) electrons
- B = number of bonding electrons (shared in bonds)
1. **Calculate for Chlorine (Cl):** Chlorine has 7 valence electrons. In ClO4–, chlorine is the central atom bonded to four oxygen atoms. Typically, assuming each Cl-O bond involves 2 electrons (1 for each atom), there would be 8 bonding electrons from the 4 Cl-O bonds:
- Valence electrons (V) = 7
- Non-bonding electrons (N) = 0 (since it does not have lone pairs in this structure)
- Bonding electrons (B) = 8
Thus, substituting into the formula:
FCCl = 7 – (0 + 8/2) = 7 – 4 = +3
2. **Calculate for Oxygen (O):** Each oxygen atom typically has 6 valence electrons. Given that in ClO4–, three oxygens are present with a formal charge of -1 (there is a total of 4 oxygens and the overall charge is -1), we check one of the oxygen atoms.
- Valence electrons (V) = 6
- Non-bonding electrons (N) = 4 (since it has two lone pairs after bonding)
- Bonding electrons (B) = 2 (one bond with chlorine)
Now substituting these into the formula:
FCO = 6 – (4 + 2/2) = 6 – 5 = +1
However, to determine the best representation of ClO4–, it’s important to note that for the ClO4– ion, one of the oxygens is likely to have the larger number of non-bonding electrons and therefore holds a -1 charge, while the others are generally neutral, giving the ion its overall -1 charge.
In conclusion:
- **Chlorine (Cl)** has a formal charge of **+3**.
- **Oxygen (O)** generally has a formal charge of **-1** for one oxygen atom in this ion.