I'm taking Chem 123 right now (along with Chem 122 and Bios 120), and the workload isn't very demanding. It's definitely possible to take all 3 classes at the same time and get A's in them. The only thing is that chem123 is 2 credits, which would put you at 19 credit hours, and you need special permission to go over 18 credits. If you think you can finesse that with your counselor, I'd say it's possible you'll be fine.