This is probably a really stupid question..

What are the reasons behind aluminum chloride being AlCl3 and Potassium Chloride being KCl? Wouldn't the subscript stay the same? Also, what is the difference between chlorate and chloride? For example, potassium chlorate and potassium chloride. Thanks again!

Potassium chlorate-potassium ,chlorine AND oxygen(thats what the ate is for) any compound ending in ate contains oxygen

ALCL3 because the aluminium has a valency of 3 so it needs 3 chlorines(which have a valency of one to make a full octet)

And potassium cloride is KCL because both the elements only have one valency

Sorry forgot to add potassium chloride is KCL because it doesn't contain any oxygen