Professor Gelbart is definitely the best prof I've had so far, and one of the best instructors I've had! While he sometimes glosses over concepts we haven't quite grasped yet, my TA was amazing and made sure we filled in all the blanks. Gelbart is also a very approachable guy, and is always kind, so never hesitate to ask questions.
That said, this was a difficult class, but 3000% worth it. There is a lot of physics and math, but I learned a lot of it on the way and turned out okay. I'd only done up to AP Calc AB in high school, and no physics, but if you take the effort to learn it, it's not that bad. This class is also awesome at giving you skills for future courses, so I would recommend you take it, especially if you're a physical science major.

Gelbart is very passionate about his subject and cares about the students. He's good at breaking down things to very fundamental concepts and drilling those concepts into you. However, he does tend to handwave away particulars and definitions (for instance, he'll use a short intuitive explanation instead of a technical word), which for some students makes it difficult to bridge the gap between lecture and reading, or between lecture and concrete problems (such as those found on tests or homework).
Attendance in class was not required; also, he did not make us commit to the discussion sections on our schedules (instead, there was a bunch of discussion sections and office hours, both with him and with the TA, and we could show up to as many as we'd like, though he recommended to come to at least two a week). Most people had more than enough time on the tests. He also was very willing to help with homework and often gave away the answer in class (also, test questions were often similar to homework questions or examples we covered in class).
You'll need to know calculus fairly well -- a lot of work is done regarding the Schroedinger equation, which requires you to be able to take derivatives and partial derivatives. There will also be some integrals required (mostly for probability; in a nutshell, you'll have a function and you'll need to give it the right coefficient so that probability "makes sense," ie adds up to 1).

I took this class solely for Gelbart and I definitely do not regret it, especially hearing all the bad things about Felker. Gelbart is a great professor who truly cares about his students and wants them to succeed. He even let us pick how many tests we wanted to have. He posts his lectures beforehand for us to go through which I highly advise along with reading the textbook which makes things easier to understand. The class definitely had difficult material but you can definitely succeed if you spend a lot of time with all the material.

The weekly problem sets were definitely very time consuming. Discuss them thoroughly with other people in the class and clarify any questions with the Professor. These are also pretty important to understanding the material so spend a lot of time with them.

Also he has 6 discussion sections/office hours either taught by the professor or the TA which are definitely quite helpful, although they often get a bit off topic about other science topics. Also reach out to him with any questions, he responds promptly and thoroughly.

Overall, definitely study the lectures thoroughly and read the textbook to supplement your understanding but don't get too caught up on understanding every little thing in the textbook. If it isn't in the lecture, it is not important. We ended up with one midterm and one final. The time was a bit hard with the midterm and I missed a ton of points for a calculus error that I didn't have time to check. The midterm was also mostly Schroedinger stuff and not much else. The final time period was definitely enough and was not too terrible, but it was a bit confusingly worded.

Overall: Just take him. You won't regret.

Lectures: Although he explains concepts, calculations and derivations in full clarity, if you are confident enough, you don't have to go to every single lecture. He posts all of his lecture notes on CCLE and they are simply amazing.

Homework: Weekly problem sets are VERY demanding. Took 4-5 hours average per week. Highly recommend to go to Office Hours and/or form a study group and solve the problems together.

Exams: He frequently mentions in class that absolutely no memorisation is required, which is 99% true (although I literally memorised all his lecture notes for the first midterm!) Very similar to homework (slightly easier than homework).

Discussions: Were usually held on Tuesdays and Thursdays. They may or may not be helpful for your understanding (depends).

Office hours: Please go to OHs if you want a good grade. Professor Gelbart is welcoming, friendly, and passionate. He also held extra office hours on Wednesdays where he talked about science in general (not necessarily related to the course).

Quantum mechanics is no joke, but I'm glad I had Gelbart to guide us. The workload for this class is pretty heavy, but it is crucial for you to understand concepts behind the homework to ensure your success in the class. Even though the problem sets are awfully convoluted, there are plenty of opportunities through office hours with the professor and TAs to get the help you need. Gelbart will patiently explain anything you have questions about, and his enthusiasm for chemistry is infectious. I would heavily consider taking this class if Gelbart teaches it again in the future.

Professor Gelbart is absolutely amazing. He truly cares about students, offering tons of office hours. The workload of the class is definitely on the heavier side because his problem sets are rather difficult. Nonetheless, they are doable, especially if you go to office hours which is how I got through it. He also provides lecture notes, which are super helpful, and though lectures are pretty dense, he does a good job explaining them, especially considering that the topics are complicated and difficult to understand. The class is not a typical chemistry class since it is about quantum chemistry/mechanics, so I would recommend having a strong math and physics background. Though I personally am not too interested in this topic, I genuinely loved the class because of the professor's enthusiasm. I would highly recommend the class for those willing to put in the work and are looking for something challenging.

Professor Gelbart was a great professor who makes time for his students - giving around 4 office hours as well as an extra science hour (for talking about science subjects of interest not directly related to the course). Homework assignments were mostly theoretical in nature, with a few computational problems and required a good understanding of the subject matter - make sure to have a good study group and ask questions to the professor or TAs! Exams were similar conceptually to homework, although not exactly the same. His lecture notes were very helpful, so the textbook was not needed as much as presumed. All in all, would definitely take again if I had a choice, great and engaging professor, challenging homework.

DO NOT. I REPEAT. DO NOT TAKE THIS CLASS WITH THIS PROFESSOR. I have never experienced a more demoralizing, strenuous, stressful, crushing, or complicated class. The teacher did not teach in class and enjoyed talking about random things that would only semi-pertain to the material he attempted to cover. Without his lecture notes and weekly homework assignments, I would have most definitely failed the class, without a doubt. This class is not what it seems. It is QUANTUM MECHANICS. The whole thing is physics and multivariable calculus. Do not take this class if you value your sleep or sanity. I worked more than I have ever worked in my life and still was not able to do well in this class. He grades unjustly and will take off points wherever he pleases. For example, on the second midterm, even though the class average was a 75, he decided to give ZERO partial credit, thus dropping up to 15 points at a time if you missed a question. Furthermore, the TAs for this course are pretty much completely useless since they have no clue what the professor is "teaching", as they never actually make an effort to read the lectures or the homework assignments before hand. You can email them or ask them questions, but good luck in getting a useful response, I most certainly never got one. The textbook is basically useless so don't buy it, just read his lecture notes the night before and do the problems at least 10 times before going in to the exam.

Professor Gelbart is the absolute best. I switched into this class just because I saw that he had such a high rating and it was totally worth it. The class itself is definitely difficult. Don't fool yourself. It's quantum mechanics, not chemistry, but he made it super interesting and he's honestly the sweetest man ever. He tries really hard to get to know his students and if you go to office hours then he'll really know you and can help in the class. He curves the entire class and gives each individual person a grade based on their effort, but overall it's a very intriguing class that's fairly graded. I love professor gelbart and I wish I could take another class with him.

Proffessor Gelbart is amazing! He's so dedicated to his students. I love his personal lecture notes and homework problems. This class is a lot more demanding than a normal 20A class however it's worth it and I'll do this class all over again if I can. Proffessor Gelbart is always so helpful, listening and answering questions whether during lecture or office hours. He cares about his students deeply and he's extremely nice and approachable. He even tries to remember all of our names in office hours. I have no disappointment about this class.

I also love the structure of the Honors class, it's small enough so we know everyone around us. I've made friends here that I think I can keep for a very long time.

Overall if you love chemistry and want to challenge yourself take this class. It's quite mathematically demanding however the main emphasis is on chemistry and physics. However, it's worth it! It'll make your fall quarter freshmen year so amazing!!!!