Today is A-level results day. The Independent reported that about 46,800 students took A-level chemistry in 2017 – the fourth most popular subject after mathematics, biology and psychology. That’s a lot of people learning about the ingredients of the universe!
While deep in the exam period, you might think the things you are revising are topics you’ll never need to remember in real life circumstances. I’m aware my job as a chemist means I’m much more likely to apply these concepts than the average person but for those of you thinking about pursuing a chemistry career, it’s useful to know what you should learn now to save you re-learning it later in life.
Having gone through the A-level Chemistry syllabus, here’s a list of things from the first module that I use in my day-to-day life as a chemistry PhD student:
MODULE 1 PHYSICAL CHEMISTRY
- Atomic structure – the study of chemistry is based on developing knowledge about the particles that the universe is made up of. In medicinal chemistry we specifically look at the molecules that make up our bodily functions an how we can design molecules that alter these functions for therapeutic benefit.
- Mass spectroscopy – an analytical technique that tells you the atomic mass of your molecule. I use this type of analysis on a daily basis in my lab to make sure I’ve made the right product – assuming the mass number I’m given matches the one I’m expecting.
- Relative atomic mass, relative molecular mass – when looking at mass spec data I have to take relative molecular masses into account if e.g. I have a chlorine atom in my molecule (35-Cl and 37-Cl isotopes give me two different product mass peaks). Also, another analytical technique I use called Nuclear Magnetic Resonance relies on the existence of 13-C in 1.1% of all carbon atoms.
- The mole and Avogrado’s constant – Moles are the typical unit used to describe a quanitity of a chemical substance, like a dozen eggs, you would talk about needing X moles of a chemical. Luckily, I use an electronic lab book that calculates the majority of mole calculations I need to do for all my experiments to work out how much of each chemical I need. I still need to be able to calculate the number of moles of a chemical I need for my reaction to work from time to time if transferring a protocol from a scientific paper to the lab book software, and also to be able to engage with the software and check its calculating the correct number of moles for my reaction.
- Empirical and Molecular formula – I often express my compounds in empirical formula (just the relative number of carbon, hydrogen. Nitrogen, oxygen etc.) as a way of keeping the chemical structures confidential. When writing up the reagents I use I often use molecular formula shorthand in my lab notebook (e.g. Chloroform = CH3Cl).
- Percentage yield calculations – again, my lab book software does a lot of these calculations for me. We use % yields a lot to express how efficient a reaction is and is a very quick way of communicating to fellow chemists how well my chemistry is working (a reaction with yield >85% are pretty good, whereas a 5% yielding reaction needs optimising!). Similarly, I still try to check whether the calculated percentage makes sense for the mass of product I have.
- Balanced equations – while I don’t write out balanced equations in the same format as I did in high school, I need to make sure the ratio of different reagents I use makes sense for the reaction I’m doing.
- Volume and concentration calculations – sometimes the prescribed concentration of, say ammonia solution, in my protocol doesn’t match what we have in the cupboard. While I can often use the lab book software to calculate how much 2 M solution I need to use in absence of 13 M solution, a solution concentration is sometimes expressed in different units (%, g/L, M etc.) so I like to do these calculations manually to make sure I can still convert between units and have the right amount of reagent.
- Knowledge of bonding – the different reagents I use in the lab have different types of bonding properties (covalent, ionic, metallic, polar covalent) which affects how they interact. When working out the mechanism of a reaction (i.e. a detailed step by step rationale for how it works) I need this knowledge to explain why a catalyst might co-ordinate to a starting material, or why a particularly strong covalent bond won’t break.
- Bonding and non-bonding electrons – again, using this knowledge when working through the mechanisms of the reactions I’m carrying out, it’s important I know which pairs of electrons will get involved in my reaction and which won’t.
- Intermolecular forces – the forces that hold molecules together or repel them (permanent dipole-dipole forces, Van der Waals, dispersion, London forces and hydrogen bonding) are really important for understanding how a drug molecule fits into a protein to shut down a biological function. When I design molecules for my specific project, it’s usually to increase my understanding of these forces and how to utilise them to make a drug that mimics an ATP molecule in the way it binds to a kinase enzyme.
- Kinetics and thermodynamics – these fundamental concepts are applied to explain why reactions go a certain way depending on different factors. It explains why my reaction needs to be a particular temperature, or why one chemical product is preferentially formed over another.
- Chemical equilibria – The equilibrium (balance) involved in a reaction can be used to explain why a reaction hasn’t gone particularly well in converting starting material to product and how I might push that reaction to go to completion (i.e. 100% product in an ideal world) by changing the concentration of certain reagents, temperature etc. (applying Le Chatelier’s principle).
- Oxidation, reduction and redox equations – Oxidation and reduction reactions are some of the transformations I apply to my molecules so being able to write reactions showing which chemical species are being oxidised/reduced is important to remember.
- Acids and bases – I frequently use acids and bases in various ways during my reactions e.g. one of my reactions involved acetic acid catalysing the formation of a benzimidazole ring system. I also alter the pH of my reaction mixture sometimes in the purification process – e.g. if a solid dissolves at a certain pH environment but crashes out as a precipitate at a different pH.
- pKa – the acidity of protons involved in my molecules is a very important aspect of predicting and explaining reactivity. I learned a bunch of pKa values during my undergraduate degree to explain why one region of a molecule is more reactive than another.
- Buffers – while I don’t personally use buffer solutions in the chemistry I’m currently doing, a lot of chemical reactions require a buffer to maintain the pH of the reaction at a certain level. The biologists I work with run different biochemical assays (tests involving enzymes and cells etc.) use buffers a lot to mimic cellular conditions when testing molecules I make for them.
I was quite surprised by quite how much physical chemistry feeds into my organic chemistry project. It just shows how much chemistry overlaps. Hopefully this shows you how useful this stuff is to know when thinking about becoming a chemist. Check back for a future post that will list the parts of A-level modules 2 and 3 that I still use as part of my PhD.
What was your favourite thing that you learned during A-level chemistry? Is there anything from your A-level days that you still use in your job today?