Question

1. which is the correct name for the compound pcl₅

monophosphorus tetrachloride
phosphorus chloride
phosphorus pentachloride
pentaphosphorus chloride

Explanation:

When naming binary covalent compounds:

• The first element (here, phosphorus) is named as the element itself.
• The second element (chlorine) has its root (chlor -) and the suffix -ide.
• The prefixes indicate the number of atoms. In \(PCl_{5}\), there is 1 phosphorus atom (no prefix for the first element when there is 1 atom) and 5 chlorine atoms. The prefix for 5 is penta -. So, it is named phosphorus pentachloride.
• “Monophosphorus tetrachloride” is incorrect as there are 5 chlorine atoms (not 4).
• “Phosphorus chloride” is too general as it doesn't specify the number of chlorine atoms.
• “Pentaphosphorus chloride” is incorrect as there is 1 phosphorus atom (not 5).

Answer:

Phosphorus pentachloride