You definitely shouldn't take it personally -- I know, better said than done. When a professor denies you the research opportunity, it isn't because he doesn't like you or thinks you can't do a good job. Often the professor may not have the money to support another student or the space (sharing a fume hood sucks!). Also, you're just a freshman and probably only have general chemistry under your belt at this point, so you're not as experienced in the lab as, say, a sophomore who has taken organic chem. It has been my experience when I did undergraduate research that the professor's grad students are the ones that helped me the most in lab, while the professor helped me critically analyze my results. Since you're relatively young and inexperience (don't take that the wrong way!), the professor needs to know that his grad students will be there to help you. Maybe under the current circumstances, that isn't possible (summer vacation, students graduating, students aren't mature enough to take someone "under their wing," etc.).
I think it's wonderful that you are seeking research opportunities so early -- motivation and ambition are a good thing. Perhaps explore this arena again after you do organic chem -- so many valuable lab techniques are learned in that class. In the meantime, there are other opportunties to build your resume in terms of lab/science experience. If your school has summer school, you could be a student TA. Or if you earned good marks, consider tutoring. You have plenty of time to do research if you desire to do -- don't be discouraged this early!
P.S. I'm not sure what type of research opportunity you are looking for (chemistry, biology, psychology, etc.) but the same principles apply. . .
