The course and the exams

🔄What changed, in four sentences

The options are gone — there is no longer a Materials, Biochemistry, Energy or Medicinal Chemistry option, and no Paper 3 built around one. The eleven old core topics have been reorganised into two concepts, Structure and Reactivity, with twenty-two sub-topics between them. Practical work is no longer separately assessed as a group 4 project plus a lab portfolio: there is one internal assessment, the scientific investigation, plus a collaborative sciences project that is required but not marked. And the papers were rebuilt: Paper 1 is now split into 1A multiple choice and 1B data-based, sat together.

What did not change is most of the chemistry. Moles are moles. If you are using an older resource for a topic that still exists, the chemistry in it is usually fine; what is unreliable is its account of what is examinable, at what level, and in what format.

📚Structure and Reactivity

The syllabus is organised around two organising concepts, and the relationship between them is stated in one line that is worth taking literally:

Structure asks what matter is: particles, atoms, electrons, bonds, classification. Reactivity asks what it does and why: what drives a reaction, how much and how fast and how far it goes, and by what mechanism. Each of the six topics is divided into sub-topics, and each sub-topic is headed by a guiding question — “How can we model the particulate nature of matter?”, “What happens when protons are transferred?” These are not rhetorical. If you can answer the guiding question properly at the end of a sub-topic, you have understood it.

Those hours are worth reading as a map of where the difficulty is. At SL the largest sub-topic block is Reactivity 3; at HL it is overwhelmingly Reactivity 3, at 45 hours out of 180. If you are HL and behind, that is where the marks are.

Woven through both concepts is the nature of science (NOS), an overarching theme rather than a topic: observation, pattern, hypothesis, experiment, model, evidence, theory, falsification, and the global impact of what chemists do. It is not examined as a separate section — it turns up inside ordinary questions, usually as “suggest a limitation of this model” or “explain why this claim cannot be tested”.

🎓SL or HL

SL is 150 teaching hours, HL 240. The extra 90 hours are not a separate HL syllabus: they are additional understandings folded into the same sub-topics, labelled Additional higher level in the guide and flagged AHL inline on these pages. Some sub-topics have no AHL at all (S1.1, S1.4, S1.5, S2.1, R1.1, R1.3, R2.1, R3.3); one, R1.4 Entropy and spontaneity, is AHL in its entirety and does not exist at SL.

The distinction the guide draws is one of both breadth and depth: HL adds content, and it also expects you to connect more of the course to any one question. The mathematical demand is genuinely higher — logarithms at SL, but exponentials, the Arrhenius equation and \( \Delta G^{\ominus} = -RT\ln K \) at HL.

If you are choosing: take HL chemistry if you need it for medicine, chemical engineering, chemistry or (usually) biochemistry at university. Take it because a course needs it, not because it sounds impressive — a 6 at SL is worth more than a 4 at HL to almost everyone.

📝How you are assessed

External assessment is 80% of your grade, in two papers sat with a clean copy of the data booklet and a calculator.

Internal assessment is 20%: one scientific investigation, about 10 hours of class time, a report of at most 3,000 words, marked out of 24 by your teacher and moderated by the IB.

Two things about the weighting that students consistently misread. First, Paper 1B is a third of Paper 1 and is entirely about handling data and experimental method — you cannot revise for it by memorising content. Second, across both papers roughly half the marks are AO3: analyse, evaluate and synthesize. Knowing the chemistry is necessary and nowhere near sufficient.

🔢The data booklet

You are given a clean copy of the Chemistry data booklet in every examination, and the guide references it constantly. It contains, among other things:

• the periodic table, with relative atomic masses to two decimal places — use those values, not rounded ones;
• constants: the Avogadro constant, the gas constant \( R \), the Planck constant, the Faraday constant, the specific heat capacity of water, \( K_{\mathrm{w}} \) at 298 K;
• equations you would otherwise memorise: \( PV = nRT \), the combined gas law, \( Q = mc\Delta T \), the pH and pOH relationships, the Arrhenius equation and its linear form, \( \Delta G^{\ominus} = -RT\ln K \), \( \Delta G^{\ominus} = -nFE^{\ominus}_{\text{cell}} \);
• data tables: electronegativities, average bond enthalpies, enthalpies of formation and combustion, standard entropies, standard electrode potentials, indicator pH ranges, characteristic infrared absorptions, proton NMR chemical shifts, common mass-spectrometry fragments;
• the triangular bonding diagram and the colour wheel.

Get a copy in week one and use it for every homework. Students lose marks not because they cannot recall a bond enthalpy but because, under exam pressure, they do not know which page it is on.

🔧Tools and inquiry run through everything

Alongside the content the guide defines three tools — experimental techniques, technology, mathematics — and a three-stage inquiry process: exploring and designing, collecting and processing data, concluding and evaluating. These are not taught as a separate unit and there is no chapter on them. They are assessed inside Paper 1B, inside Paper 2, and inside the IA.

The most examinable parts, and the ones students are least ready for:

• Uncertainties. Record as a range (±), propagate by adding absolute uncertainties for addition and subtraction, and percentage uncertainties for multiplication and division. AHL also for exponents, where you multiply the percentage uncertainty by the power.
• Percentage error against percentage uncertainty. Error compares your value with the accepted one; uncertainty comes from your instruments. If the error is much larger than the uncertainty, something systematic is wrong — and saying so is worth marks.
• Significant figures. Quote a processed answer to the precision of your least precise measurement, not to whatever your calculator produced.
• Graphs. Sketching with labelled but unscaled axes to show a trend; plotting with proper scales; gradients, intercepts and areas; uncertainty bars; and \( R^2 \) as a measure of how well a line fits.
• Techniques you must have met: preparing a standard solution, serial dilution, drying to constant mass, distillation and reflux, paper and thin-layer chromatography, calorimetry, acid–base and redox titration, electrochemical cells, colorimetry, recrystallization, melting point determination and molecular modelling.

📋Command terms — read the verb

Every question is built on a command term with a defined meaning, and answering the wrong one is the cheapest way to lose marks in this subject. The ones that most often go wrong:

• State — a name, value or brief answer. No explanation, no working. Do not write a paragraph.
• Describe — a detailed account of what. Explain — a detailed account including why. If your answer to “explain” contains no “because”, it is a description.
• Deduce — reach a conclusion from information given. Determine — obtain the only possible answer. Suggest — propose a possible answer, so more than one may be creditworthy.
• Compare needs similarities referring to both throughout; contrast needs differences the same way. Two separate paragraphs, one on each substance, does not compare them.
• Calculate — show the stages. Determine and calculate both mean working is credited, so an unsupported final answer that is wrong scores zero where working would have scored most of the marks.

🧭How to use this site

The rail on the left lists every sub-topic in syllabus order, and the prev/next links at the foot of each page walk you through the whole course. If you are revising for a test on one sub-topic, open that page and work down it; if you are revising for a mock, use the hub and take a topic at a time.

Each sub-topic page ends with six practice questions whose answers state the method, not just the number. Attempt each one on paper before revealing the answer — reading a worked solution feels like learning and mostly is not.