To calculate the formal charge of chlorine in various molecules, we will use the formula:
Formal Charge = Valence Electrons – (Non-bonding Electrons + 0.5 Bonding Electrons)
a) Cl2
In diatomic chlorine (Cl2), each chlorine atom has 7 valence electrons. There are no non-bonding electrons and each chlorine is bonded to one other chlorine atom, sharing a pair of electrons (which counts as 2 bonding electrons).
Calculation:
- Valence Electrons = 7
- Non-bonding Electrons = 6 (3 lone pairs)
- Bonding Electrons = 2 (1 bond)
Formal Charge = 7 – (6 + 0.5 * 2) = 7 – (6 + 1) = 0
Therefore, the formal charge on each chlorine atom in Cl2 is 0.
b) BeCl2
In beryllium chloride (BeCl2), beryllium is bonded to two chlorine atoms. Each chlorine atom again has 7 valence electrons. In this case, each chlorine is involved in a bonding situation with beryllium, sharing two electrons.
Calculation for Cl:
- Valence Electrons = 7
- Non-bonding Electrons = 6 (3 lone pairs)
- Bonding Electrons = 2 (1 bond with Be)
Formal Charge = 7 – (6 + 0.5 * 2) = 7 – (6 + 1) = 0
So, the formal charge on each chlorine atom in BeCl2 is also 0.
c) ClF5
In chlorine pentafluoride (ClF5), chlorine is bonded to five fluorine atoms. Each fluorine atom has 7 valence electrons, with 6 non-bonding electrons (3 lone pairs) and all are involved in bonding with chlorine.
Calculation for Cl:
- Valence Electrons = 7
- Non-bonding Electrons = 0
- Bonding Electrons = 10 (5 bonds with F)
Formal Charge = 7 – (0 + 0.5 * 10) = 7 – 5 = 2
The formal charge on chlorine in ClF5 is +2.
In summary:
- Cl in Cl2: Formal Charge = 0
- Cl in BeCl2: Formal Charge = 0
- Cl in ClF5: Formal Charge = +2