Question

Why is alcl3 called aluminum chloride but pcl3 is called phosphorus trichloride?

Answer 1

Aluminium has a valency of 3 and form AlCl3 known as aluminium chloride.

But in case of phosphorus, it has two valencies 3,5 and forms two types of chlorides, Trichloride and Pentachloride.

Usually with element having more than one valency, we need to add a prefix so that we are more specific abut what the compound is.

Answer 2

Explanation:

the prefix dry or Tetra Penta acid is added as in case of Management for example pcl3 is it cost for a striking a ride and PCL5 is Phosphorus pentachloride in which element has a valency of three positive and forms aluminium chloride but in case of phosphorus it have variable valency of the element having variable valency we have to add perfect like try or Tetra