Professor Lin's workload is very heavy, as he requires you to submit "previews" before every (mandatory) lecture/discussion (these two are combined into one, the TAs don't do much except during their own office hours, since Professor Lin pretty much takes over discussion sections) as well as one problem set per week. However, taking the time to really master his previews and problems sets helps out a lot in studying for his two midterms and the final (or self evaluations, as he likes to call them). If you can do the hardest problems on the homework, then the exams shouldn't be any more difficult.

In addition to the exams being relatively straightforward, Professor Lin is also a very kind and generous man, as on many occasions, he brought the class chocolates, pizza, Subway sandwiches, and even gave each of us a mug with our class picture on it before the quarter ended. He even gives you one (literal) free lunch with him, redeemable once before you graduate UCLA if you successfully finish his class and later on want to contact him just to chat about school/research or even to ask for a letter of recommendation for jobs or for graduate/medical school.

I enrolled in honors by accident, and it the best mistake of my college caREER so far. This class really ignited my passion for chemistry, and I knew that I had made the right choice to be a chemistry major. Professor Lin is kind, enthusiastic, and really cares about his students' academic understanding. I would recommend this class to any chem or biochem major, and others in the physical sciences who are interested in quantum mechanics (and dank memes). However, you really do need to be willing to put in the work--the daily homework and weekly problem sets are not a joke. Professor Lin does sometimes get off track in his lectures, because once he starts talking about science, he just can't stop. This means that going to office hours (held daily and sometimes even on the weekends) are super important in order to really understand what you're doing (simple snacks are also provided). Professor Lin's accent can also take a few days to get used to...he can talk fairly quickly and blur some words and terms together. One of the best parts of the class for me was its small size. I was really able to connect with other people in my major and make study buddies. Also, basically all of my friends are people from 20AH...when you spend at 15 hours a week suffering alongside your peers, you build a strong bond. I would definitely take a class with Professor Lin again and hope you all get the chance to, either for your caREER or for mere ENTERTAINMENT.

This class was an amazing experience and I would highly recommend it to any biochemistry or chemistry major or anyone who wants to get their mind blown by QUANTUM MECHANICS.

Professor Lin is an outstanding teacher, is super passionate about the material, and is very concerned about students. However, his passion sometimes means he gets sidetracked during lecture. But even these tangents are helpful in remembering the material. For example, I will forever associate blackbody radiation with Naples and the Alaskan wilderness.

But beware, this class does require a lot of work. We have daily homework and weekly problem sets (which can be lengthy) . Additionally, in my experience, the daily office hours (with complementary snacks) are crucial to gain a TRUE UNDERSTANDING of the material.

Exams are very straightforward as long as you do the homework, pay attention during lecture, complete the practice exams, and understand any derivations shown in class. These tests are 3 hours long but he provides Subway sandwiches. Professor Lin emphasizes conceptual understanding over memorization so all formulas are provided.

One major benefit of the class is its small size. This means you get to develop a good relationship with the professor and your classmates. I made the vast majority of my friends through this class and the massive amounts of time we spent studying together.

Overall, 1000000/10 would recommend.

Lin is a very great prof. He really makes me learn a lot. After my first midterm I got a 98 and he sent me an personal E-mail and told me how great I did. He really helps you understand quantum mechanics and also holds super lots of office hours and he wants you to succeed in his class. This class requires a lot of work but you can also get a lot form this class. He is also going to write me a recommendation letter. Nice guy, very approachable some people might not be comfortable with his Chinese accent, but his speaking is okay for me. Strongly recommended.

Professor Lin was my first professor at UCLA and he's one I'll never forget. He really cares about his students and works hard to make sure you do well. Don't get me wrong, the class is extremely difficult and you have to put it a ton of effort, but if you try, and really pay attention to the practice tests he gives you, you'll do fine.

I totally agree with my classmate's remarks one floor below me. Just add one more comment here. In addition to clear physical picture and inspiring insight, Professor Lin told good jokes, too. Why carrot should be white? How to form a group of boy scouts? Two-body to one-body to no-body transform?! (I am laughing now.) It is even more amazing to see how Professor Lin effortlessly connects his lecture to state-of-the-art research and current fundamental challenges in chemistry (how to steal zero-point energy? how to do cold fusion by quantum tunneling?). Take his course whenever possible. But it will take you enormous amount of time to study, think, and do daily previews and weekly problem sets, in order to excel in his course.

Don't take this class if you can't invest 13 hours of lectures and 5 hours of self studying per week. Prof Lin's accent will confuse you in the first couple of days but you'll get use to it, so on so forth.
It is very hardcore commitment but also an eye opening experience, you'll learn mostly about quantum chemistry, stuff like Feynman Double Slit, Angular Momentum, Simple Harmonic Oscillator, and Collapse of Wavefunctions.(Shuuuuuuuuu).
Love prof. Lin, best Prof ever, 5/7, would take again.

Don't be scared by how much people complained about CHEM 20AH and miss such a brilliant class!!!

>General guidelines before me babbling every aspect of this class:

DON'T take this class if:
•you're not a chemistry person and AP chem is already a struggle for you. (90% of this class is not relevant to AP chem. The only things that appear are orbitals, VSEPR and other relevant chemical structure stuff, and they're the easiest part of the whole class.)
•you're relatively slow at understanding new concepts. (Most of this class are new theories that basically overthrow whatever you've learned about chem and classical mechanics.)
•you're not ready for 15-35 hours of chem study per week besides lectures and office hours. (The real time spent on this class varies from person to person though).
•you are good at chem but bad at physics. (This class is physics-heavy.)

>Reviews about class:

((Please notice that this review is a personal one and might be prejudiced since I love Professor Lin and CHEM 20AH.))

Professor Lin is the best professor I've ever had and he gives best lectures. The lectures are clear and engaging, and professor uses some (often really funny) real life examples to introduce new concepts. This class is the only one that I've never checked my watch to see how much time remains. The Professor also stresses on the hard stuff and repeats them over and over again to make sure that everyone truly understands everything -- don't get bored and play on your phones when you think he's going over old stuff again becuase some of them might be new stuff or deeper analysis of old material. The only thing to notice that the lectures are some times way behind the previews you're doing so make sure you don't mix up the concepts.

As for the workload, it is indeed heavy but not THAT bad at all. (Honestly I felt some other course I took this quarter took much more time than chem). The Professor always gives the homework early and you get plenty of time to finish them. Do it ahead of time if possible. Don't wait for the last office hour to get hints and start working the night before the due (you can do that for daily previews but don't do that for problem sets becuase you'll probably suffer a lot).

Going to office hours is really helpful because sometimes the problems takes one or two hours to solve without hint. (But I actually found that solving problems by myself made me understand all the materials better. Personally I think taking the painful procedure of struggling to solve the problems and then going to his office hours to see how to solve them in a more intelligent way is the best way of doing the homework.). Also sometimes office hours are more like small lectures so don't miss them.

The most important thing that I earned from this class, besides all these precious knowledge of quantum chemistry, is personal attention from the professor. Everyone knows that it is SO HARD to get personal attention in such a big school, but professor Lin really cares about his students. He gives us snacks and presents, answers questions with patience, and most importantly, replies to emails really quickly. (I actually sent emails several times at 2 or 3 am and he still replied in like half an hour).

Plus, you'll make lots of friends in this class because of the small class size, and that's another good thing about CHEM 20AH!

P.S.: I'm definitely taking C113B with Professor Lin next quarter!!

This course is so hard, so helpful, so enjoyable, and so exciting all at the same time. Going to Lin's 11am "quantum paradise" and 4pm office hour every weekday has become my most important daily activity. (I am thinking about going to Lin's Sunday bonus office hour when exams come.) I have decided to change my major to chemistry and take Lin's Chem 113B next quarter. It's very fortunate to have Lin as my first professor at UCLA. I have also made a few new friends in this academic family. (We studied together to try to survive.) My cousin (a graduate student at Berkeley) took Lin's Chem 115A and 115B before. He told me Lin is very supportive to his students and write very serious and powerful recommendation letters and warned me Lin has very high expectations. He is absolutely correct. We have homeworks(daily preview and weekly problme set) due every weekday. It forces me to study and do exercises a few hours every day. Perhaps that's why I did so well in the first midterm. Both Lin's 20AH and office hour snack are "additive" :)

This class is so hard that it builds a community from the students that have suffered through it. You will probably not meet everyone, but you will know who everyone is and who knows how to do the homework. I remember many nights of frantic phone-calls as people tried to get the correct solution to the preview or the problem sets.

It was a lot of work but it was also one of the best classes I have ever taken. Be warned; you may end up changing your major after the quarter is over.