Chemistry A

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Chemistry A is the more mathematical and physics-related Chemistry subject in Part IB, which spans both the theoretical and physical branches of chemistry. It builds up well on the foundations of Part IA Chemistry, with relation to the courses on Shapes and Structures of Molecules, Thermodynamics and Kinetics. While the Chemistry A course may appear to require an abundance of mathematics, the key mathematical concepts have been well covered in the Part IA Mathematics A/B course, with most calculations being well expounded in thorough explanations in the relevant lecture notes. The theme of the course revolves around using fundamental concepts like quantum mechanics and symmetry to predict structure and bonding, statistical thermodynamics, kinetics, and the bulk properties of materials, while using spectroscopy for experimental analyses.

As usual, most lecturers leave some blanks in the notes/examples to be annotated during the lectures (though the last course in Easter will be provided in full to allow for more flexible revision strategies). Lectures are usually held at 12pm on Tuesdays, Thursdays, and Saturdays unless informed otherwise.

The course is exceptionally well-structured and provides appreciable motivation for students to learn various theoretical and physical concepts. As the course progresses, future topics will draw on concepts learnt previously in past lecture topics, bringing everything full circle by the end of the course. The lecture series are outlined as below:


  • Introduction to Quantum Mechanics: The year kicks off with the quantum mechanics lecture series which will span across more than half the term. This is arguably the most important series in the course, as future topics will be built on the concepts learnt here. You’ll be exposed to wavefunction manipulation, hermicity, angular momentum, and the usefulness of orthogonality. The series will also include all-important models like the free particle system, (an)harmonic oscillators, and the rigid rotor, with their own relevant properties, which will be quintessential for future topics. Other more familiar ideas will be discussed further in depth, such as the hydrogen atom model, multi-electron system, Pauli Principle, and Hund’s rules in relation to quantum mechanics concepts. Lastly, the course rounds up with the cryptic Variational Principle, and a sneak peek into the Hückel method to calculate minimized MO energies.
  • Molecular Spectroscopy: Spectroscopy is the most experimentally relevant course. It seeks to use the principles learnt from quantum mechanics to rationalize experimental spectroscopic data in conjunction with relevant selection rules. Both Infra-Red (IR) and Raman spectroscopy will be discussed, in relation to rotational, vibrational, and electronic spectra. Half the experimental practicals will be based off concepts learnt in this series, and thus going through the content here will help motivate the experiments, measurements and analyses made there, and provide good revision for the viva session (see Practical section for more details).


  • Symmetry and Bonding: (Note that the few starting lectures will likely take place during the end of Michaelmas). Prepare your 3D spatial reasoning abilities, because in this lecture series, you’ll be visualizing and mentally rotating LOTS of molecules. The course first lays down the foundations of symmetry, explaining relevant information about symmetry operators and point groups (N.B.: group theory but not so much mathematically – in a more relevant manner to chemistry). These ideas lead on to various techniques, like constructing irreducible representations (somewhat confusingly also acronymised as I.R.), forming symmetry orbitals (SOs) and applying direct products. Linear combinations of atomic orbitals (AOs) and SOs of similar symmetries then give an insight into how MOs eventually form, with their relative energies eventually calculated through Hückel calculations, which will be explained in detail (with extensive approximations). There will be a section on the symmetries of transition metal (TM) complexes which ties in nicely with the Chemistry B lecture block on TM chemistry as well. Other parts of the course include a further in-depth explanation of term symbols in the context of symmetry, how symmetry can be used in spectroscopy, and a newer section on the symmetries of polyatomic rings and chains.
  • Molecular Energy Levels and Thermodynamics: Remember that little segment on statistical thermodynamics in Part IA Chemistry? Well, it’s back, and it’s back with a bang through 14 lectures of exhilaration. There will be minimal classical thermodynamics here, as we use concepts from quantum mechanics to pave the foundations of the statistical thermodynamics, embodied in the fundamental idea of the molecular partition function. Expressed through the idea of a system existing in individual microstates, the partition function is broken down into translational, rotational, vibrational and electronic contributions, which are used to demonstrate trends in internal energy, heat capacity and entropy. There will also be a section on nuclear spin statistics, accounting for the variation in intensities in spectroscopic measurements. The partition function can then be used to explain familiar concepts in chemical equilibria, giving rise to expressions like the Saha equation and the Langmuir isotherm, and in chemical kinetics, estimating rate constants and discussing the volume of activation. The series then ends off with a short note on the Boltzmann distribution and density of states.


  • Electronic Structure and Properties of Solids: This series draws on everything that has been covered thus far in the Chemistry A course and serves to bring the course back in full circle. For those who have taken material science, the introductory concepts here will appear familiar, such as crystal structures and Bravais lattices. The first part of the course revolves around exploring the structure and bonding of solids, via the free electron gas (FEG) model and tight binding model which gives rise to electron bands, which will both be explored in 1D, 2D, and 3D. These models can then be used to explain the bulk properties of solids and will lead nicely into the second half of the course, which explores the chemistry behind semiconductors in greater detail, with a few examples of semiconductors devices like the p-n junction and bipolar junction transistor. The lecture series then finishes with a discussion on spectroscopic measurements in semiconductors and their relevance to band gaps, with a brief touch on phonons and excitons.


Each lecture series has a list of supervision questions that assist you in understanding the various concepts covered. They are often quite well structured, such that after each lecture, it will be clear which questions can be done based on the content covered thus far. As such in terms of question planning for supervision work, it is generally advised to keep up with the relevant questions as the lecture series progresses (though this is admittedly not easy!). Some supervisors will choose to skip questions which may be repetitive in the skills practised, but students are highly encouraged to complete all supervision questions eventually in preparation for the exams, as they really provide the much-needed practise to tackle Tripos-style questions within a time limit.

(An important note is that you will not be expected to learn the detailed mathematical derivations behind some topics & equation solutions, often having to just accept the solution as it is, which is generally what’s only required for the examinations. This can however be understandably frustrating for some who wish to understand the topic more thoroughly. It is advisable to discuss certain concepts and proofs you wish to find out more of with either your supervisors, lecturers, friends, or pretty much anybody you can get a hold of to avoid the usual “you’ll learn this next year” or “you won’t need to be knowing this so don’t worry”.)


Part IB Chemistry A, like Chemistry B, has a weekly practical session in the afternoons from 1.45pm to 6pm. There will be 12 practical sessions in total with 6 each a term (2 free weeks), alternating between computational and experimental practical sessions. There will be a practical lab booklet for each term, which compiles all the relevant information and taskings required for each practical, as well as more detailed information on the practical sessions and marking schedules themselves.

After each session, you will have slightly short of 2 weeks to compile your data and present it in a write-up that is to be submitted online on Moodle at least 24 hours before the start of your next computational/experimental practical. This is to give enough time for your senior demonstrator to review your work and prepare for the viva session which takes place during that practical session. Each practical is marked out of 20, 10 for your write-up, and 10 for your viva session. During the viva marking session, you’ll be asked to give an overview of what you have done in the write-up and answer some questions about the theory behind the practical itself (mainly concepts from the lecture series). The senior demonstrator’s goal is to ensure that you understand the purpose and objective behind each practical, and you’ll be assessed based on your understanding of the practical and theory behind it, so be sure to do a little revision of the relevant theory before your viva session!

E.g. Your practical session is on Wednesday afternoons. You spend the whole afternoon hammering away at your excel sheet for computational practical A and possibly spending the rest of the week on it as well. You must submit your completed report by the Tuesday two weeks later before 1.45pm. On the next computational/experimental session the next day (Wednesday), you pull up to the respective location and work on your next computational practical B.  During the session, you’ll be called up for marking for computational practical A, and the cycle repeats until the end of term (hence the additional 2 weeks meant for marking).

Computational sessions are usually held in the G30 room, where there will be a junior demonstrator around during practical hours (until 5p.m.) to assist you should you need any help (similar to Part IA Math practical sessions). Python is primarily the main programming language used for coding, though you’ll have the opportunity to use other open-source programs like Avogadro and ORCA for ab initio calculations. Content is mostly drawn from the quantum mechanics course, and a bit from the symmetry/bonding and statistical thermodynamics course. Experimental sessions are held in the Physical Lab? Most experiments are generally quite fast, and majority of your time will be spent on analysing the data obtained. Half the experimental practicals will be on some form of spectroscopy, while the other half varies in content.

Revision and Exams

It is absolutely essential that your revision is centred around timed practise of past year papers, as practising on Tripos-style questions are the best way to prepare for the Tripos itself. There are up to 25 years of past papers to complete in total, with suggested answers provided by faculty members to guide you towards the correct answer as you mark your work. The quality of these answers varies extensively, from some being highly detailed to others with almost illegible handwriting, so it would be best to check and discuss these answers with your supervisors as well. Keep in mind that for some lecture series, the lecture content has changed over the years (especially the last series on Electronic Structure and Properties of Solids), so keep a lookout for a section on suggested Tripos questions at the back of the respective lecture handout which will list the question (parts) that are still relevant to the current content.

Chemistry A is examined via two 3-hour-long papers: Paper 1 and Paper 2, each with 5 compulsory questions. In recent years, Paper 1 contains 2 questions on Quantum Mechanics (QM), 1 question on Spectroscopy, and 2 questions on Symmetry and Bonding. Paper 2 contains 3 questions on the Statistical Thermodynamics course, and 2 questions on the course on Electronic Structure and Properties of Solids. Especially for Paper 1, time control can be a real issue, due to the mathematical nature of QM questions, and the repetitive nature of Symmetry and Bonding questions. You should spend an average of 36 minutes on each question. It is recommended to get as much practice as possible to speed things up during the actual examination.

N.B. Do note that the format of papers has changed in 2012 from choosing 5 questions from 7 to answering all 5 compulsory questions for each paper – giving you more questions to practise.

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