What is the oxidation number of phosphorus in the compound #"PCl"_5"#?
In the case of phosphorus pentachloride,
Since chlorine is more electronegative than phosphorus, you can assign its oxidation number by assuming that it takes all the bonding electrons used in the molecule.
Since each single bond contains
So, for each bond chlorine has with phosphorus, it gains one electron; at the same time, phosphorus loses one electron. This means that the oxidation state of each chlorine atom will be
The phosphorus atom loses a total of
The oxidation number of
The sum of oxidation numbers in a compound must be zero. The oxidation number of chlorine in