Western Chemistry offers many electives, some are for the broader Western community, some have advanced course pre-requisites, some have no restrictions. Some chemistry third year electives are popular among Biology and BMSc students, other courses attract Physics students, and selecting the right courses can be complicated.
So, let’s simplify the offerings without all the details. First, anyone that meets the pre-requisites can take these offerings at any time. For example, you can take a forth year course in your third year, but be aware of restrictions and anti-requisites.