Chem 20B with Weiss is very very different than with Li. It's really not fair how different the two classes are in terms of difficulty. Weiss goes over at least three more chapters than Li does and his grades are much lower than compared to Li. That being said, Weiss is a fantastic person and extremely helpful, but his class is very frustrating. There is homework due each lecture, accompanied by around four sections in the book each time. This homework often takes a 1.5-2 hours if you do all the reading. The homework is graded and counts for 30% of the class. While most may see this as a good thing, the TA's almost always handed out 2/3 for the homework, which means you're losing 10% off of your final grade. In addition, the reading and homework have nothing to do with what is covered in lecture. It's like taking two separate courses within one. The homework is mostly equations and numbers-based, while the tests are entirely conceptual. It makes no sense. I can see how a chem or biochem major would enjoy this class, but as an engineer who just wants to fulfill his chem requirements so he can move on, this class was very unenjoyable.
TL;DR Only take this class if you really love chemistry. Otherwise, take Li. Actually, just take Li no matter what.

Taking Chem 20B with Weiss was probably the worst thing I've done at UCLA. My motto is "KNOW THE MATERIAL SO WELL YOU CAN PERFORM IT IN YOUR SLEEP". I did that for hos class, too. I did the all-nighters, I put in 60+ hours of study per midterm (3 in his class) enough to make you feel prepared, but no, the midterms were wholly focused on things that shouldn't even be in the 20B syllabus.
He had homework due EVERY lecture, and most times, the TA's would give you 2/3, leaving you with a C average on the homework, which was worth 30% of the total grade.
The final exam included material that did not have anything to do with the course.
Coming from a big time chem lover, if you still want to like chem or even pass it, take it with some other professor. Weiss is a nice man, but you can tell he is more of a researcher than a professor.

I learned a LOT in his class. He's such a sweetheart, but homework is worth 30% of the grade, and it's due every lecture. If you love chemistry, you'll love Weiss. If you hate chemistry, you'll hate Weiss.

That said, your experience is based mostly on your relationship with your TAs. If you get his class, PLEASE PLEASE make sure that you get a good TA. I got lucky, but I've heard horror stories about TAs who refused to change the grade because, although he wrote the right answer, she didn't feel that he got the answer right.

Get a good TA, do your homework, ask Weiss something about semi-conductors, and you'll get an A. Guaranteed.

Even Weiss himself recognized that Winter 2016 was grueling, so he modified his class waaay more so that it was actually doable lol. A lot of the old reviews scared me so much after I got stuck in his class, but honestly it wasn't so bad. My biggest complaint is the workload, since homework was due every lecture, but didn't actually help much for tests (homework was book problems so very quantitative, yet we couldn't even use calculators on exams). Weiss is obviously very knowledgeable in his field and likes to name drop a lot of distinguished people with whom he's worked with (awe inspiring or yawn inspiring is up to you lol). He takes feedback pretty well, and even though I was a bit annoyed with how he designed his class, I do felt like he actually cared about the students. He often did reviews before midterms/ the final, as did his TAs, which were immensely useful since it was easy to get confused during some of his lectures (he gets excited easily and goes on tangents, especially if some students asked some non sequitur questions). If you go to the review session and review his recaps and such you should be fine. The only curveball I didn't like during exams was in the first midterm when he asked about acid/base stuff although we barely covered it (this should tell you that Weiss likes to preview new stuff in his midterms so beware and study more newer stuff than older stuff)
Like the person below said, however, Weiss did mention that the next time he'd teach this class is as an honors class, which makes sense because I feel like only the really passionate chem people would put up with the amount of work he has you do. Overall, he's kind of a funny uncle type of person, but he really does know his stuff

Do you like hours of daily homework assignments, not covering anything in lecture, and being tested on things you never learned because the professor was too occupied with bragging about his personal achievements to actually teach? Me neither, but that's the gist of Weiss' class. For the first half of the quarter we would cover roughly one to two powerpoint slides during an entire class period. I would have just stopped coming, except that lectures were how we turned in our daily homework assignments that constituted several hours of reading and textbook problems the night before. Weiss also assumed that we had already learned thermodynamics (the main topic of this class) in high school and thus didn't cover it in his own lectures, just assigned extra homework on it as "review". The discussions are also mandatory because any given week you might have a graded quiz on what you supposedly covered in lecture that week. When asked a question, Weiss will likely derail entirely from giving any sort of sensible answer and instead talk about something he did with his kids one time. There are no study guides for the exams, just a long list of possible topics which is actually just a list of all the course material. One nice thing is that the TA's, who are all just people who work in Weiss' lab, host review sessions before the exams. The unfortunate part is that the sessions always go at least an hour longer than expected, spend a very long time on basic concepts, and then speed through the advanced things. The tests themselves are often worded in a confusing way and are not similar to the homework problems. They are equally conceptual and computational but you are not allowed a calculator.
TLDR: Unhelpful, lots of homework, mandatory lectures and discussions. If you value your free time or GPA, avoid this class.

First off, Professor Weiss loves chemistry and loves teaching it; however, as evident from numerous other reviews, this doesn't always translate to the best learning environment for students.

The class really is structured more like an honors class--which is what he taught for 8+ years at Penn State. Yes, the homework load is heavy and graded hard. Yes, the tests really cannot be studied for and do indeed test your ability to think and reason chemically. Yes, his slides are quite complex and hard to absorb.

BUT, though this class, you can really gain an appreciation for true chemistry that is applicable in the real-world rather than in the crappy book. I am a mechanical engineering student and am actually sad now that this was my last chem class.

I WOULD NOT recommend taking this class if you're looking for an easy, good grade (that's Li). I WOULD recommend taking chemistry with Professor Weiss if you're up for a challenge and tests that conceptually prod your understanding of chemistry to previously unattained depths.

This professor inspired me to pursue materials science/chemistry even though I'm originally a biochemistry major.

He's highly overqualified to teach the material for this class which is on par with AP/IB chemistry level material, so basically he gets really bored with the material and goes on tangents and tells stories about actually interesting things that go on in the chemical world. Come the first midterm, I was afraid that all this application would get tested on but turns out it wasn't, or at least for 95% of it. In fact the tests go over material that he heavily emphasizes nearly everyday, or does demos for or that the TAs go over.

And for the TAs, he pulls them from his own research group so they make for a really great team to provide all the resources and proper learning experience for you.

For the material itself, throughout the quarter he covers topics that will appeal to everyone's major, from chemical engineering, to biochemistry. His office hours are a bit different in that it functions more as storytime where he talks about really fascinating things that he's working on or other people in the department.

The tests are actually pretty easy but require you to understand the material and more importantly understand what he emphasizes to you. His goal in this class is to build your chemical intuition so he will test on it. He doesn't care for memorizing or naming things but he cares more for understanding chemical relationships and WHAT will happen and WHY.

I don't know how much use this review will be considering he mentioned he is trying to teach the honors section next year, but the reviews from last year are from when he aimed higher and expected more from the students although he says it didn't work out how he foresaw it. Winter 2017 was easier and less information heavy than Winter 2016, the last time he taught 20B

This class is basically just a stupid amount of work . I spent about 20 hours (not exaggerating) on homework that was due EVERY class and went to office hours at least once a week. I scored above average on tests, but the homework is what kills you. Get a good TA, have them look over your homework/do the problems in OH. Weiss is not a good teacher, so you'll be relying heavily on your TA's. Weiss didn't curve for our class.

Let me start off by saying this: this professor has certainly gotten MUCH better from the last time he taught. That being said, he is still pretty much garbage. He has improved in the types of questions he asks on his midterms/final, and the relevance of those questions to what the course is suppose to be about (solubility, acid base, thermodynamics, gas laws, etc,, ya know, chemical energetics and change). However, he still goes off on tangents about the most useless topics ever, has terrible jokes and a terrible laugh, and still doesn't know how to teach. But he apparently did read his reviews at the end of the year and changed up his tests this quarter, which is a great sign compared to what he was testing on before (mass spectrometry, DNA, proteins, spectroscopy, stuff he talks about in his tangents basically). Basically, better tests, terrible teaching skills

I would highly recommend anyone else in terms of Chem 20B, but if you're stuck with Weiss, realize that there is still hope. THIS SAVED ME: if you write on your test that you realize that your answer is wack and completely wrong, or write down two answers and point out that you believe that one of them is correct, you will get some points back! In this class, ever. point. matters. In order to be successful, make sure you:

gather up all the points from doing the homework (10%)
Make some creative problems (5%)
Submit your homework on time (5%)
Do those reading memos (5%)
Show up to every discussion to take the quizzes (10%)--doing the example problems in the textbook will help with this! The textbook isn't great, but it's going to be your only guide in understanding the materials in this class. The TA can be decent, but I had a bad TA :/

Doing all those above to the best of your abilities is already 35% of your grade. And you are going to need every single goddamn point in this class. Make sure to go to the review sessions before every midterm; those will be your saviors for this class. As far as tests go, your best hope is the review sessions, past tests in the bruin test bank (try to get the more recent ones); his powerpoint slides aren't great and would not recommend you to use those.
The homework vs. what the TA's say in discussion vs what Weiss says vs. the tests are all going to be different. Good luck.

This class is basically high school AP Chemistry with very few new things thrown in. The only part of this class that sucked was the homework. It doesn't seem like much on paper, but the textbook problems are pretty convoluted. The exams were fairly simple and in almost no way related to the homework, so feel free to Chegg the homework or something to get full points on that. The exams were graded pretty harshly due to their simplicity, so be wary of that. Just study with people who've had good experiences with AP Chem, and you should be fine.