Glad you mentioned Clementine. That's a great example of a chapter book series. Another one is Judy Moody. Chapter books tend to run from about ages 7-10 and some are quite a bit shorter than MG novels, running only 10-12K. I've noticed that chapter books usually run in series -- they are about the *character* primarily -- and the MC is typically in third grade. Though I'd look again to verify, I'm pretty sure Paula Danziger's Amber Brown series would be considered chapter books. Chapter books are also big on humor.
MG novels run from about ages 8 or 9 to 12. They can more easily stand alone, either plot or character can be in the forefront, and though there's a range, they can be a lot longer and a lot more complex with more layers and subplots.