Marks-weighted analysis of 248 questions across 825 marks and 15 papers — every sitting of the redesigned IB Chemistry Higher Level course so far. Structure and Reactivity theme weightage, the Paper 1A / 1B / 2 split, and the cross-topic synthesis that now dominates the exam.
The 2025 course is built on two concepts — Structure (what matter is made of) and Reactivity (what it does) — split into six themes, S1–S3 and R1–R3. Below is the percentage of total exam marks each theme carries across all 15 papers, with marks distributed among tags to avoid double-counting.
Particles, the mole, electron configurations, gases, bonding models and the classification of elements and organic compounds. Structure is the language the rest of the course is written in.
What drives a reaction, how much / how fast / how far it goes, and the mechanisms by which protons, electrons and electron pairs move. Reactivity is where the majority of marks — and almost all the hard ones — sit.
Proton transfer (acids and bases), electron transfer (redox and electrochemistry), radical reactions and nucleophilic mechanisms together take almost a quarter of every mark on offer — more than any other theme by a wide margin.
The two concepts are close to an even split, so neither can be treated as the "main" one. Structure earns its share largely through the mole and bonding; Reactivity through mechanisms and kinetics.
Models of particulate matter and the how-much / how-fast / how-far theme are the calculating heart of the paper — moles, concentrations, yields, rates and equilibria. Arithmetic fluency is worth over a third of the exam.
Even the lightest theme, R1 (what drives reactions), still carries 11.4% of marks and appeared in all five sittings. There is no theme small enough to gamble on skipping.
Every sub-topic ranked by its share of total exam marks. Bars are coloured by theme — cool colours for Structure (S1–S3), warm for Reactivity (R1–R3). Sub-topics marked +HL carry additional Higher Level content on top of the SL material.
Stoichiometry, empirical formulae and concentration is the single largest sub-topic — and it is wildly paper-skewed: 7.2 marks on Paper 1A, 24.9 on Paper 2, and a huge 49.6 marks on Paper 1B. If your mole calculations are shaky, the data paper is unwinnable.
R3.2 Electron transfer (9.81%) and R3.1 Proton transfer (8.78%) are the second and third biggest sub-topics. Between them they carry nearly a fifth of the whole course, and both appear on all three papers every sitting.
Unlike the old course there are no HL-only sub-topics. The extra Higher Level demand is folded into existing topics — Born–Haber cycles in R1.2, Gibbs energy in R1.4 and R2.3, rate laws and Arrhenius in R2.2, buffers and titration curves in R3.1, cell potentials in R3.2, SN1/SN2 in R3.4, hybridization in S2.2 and transition metals in S3.1. HL students meet them in the same questions as SL content.
No single "organic" topic exists, but S3.2 functional groups (6.8%), R3.4 nucleophilic reactions (3.83%) and R3.3 radicals (2.13%) combine into an eighth of the exam — and they are almost always examined together in one long Paper 2 question.
The smallest sub-topic by marks, followed by S1.2 The nuclear atom (1.2%) and R1.3 Energy from fuels (1.4%). All three still surfaced across the five sittings, usually as a single multiple-choice item or a short definition. Low weight is not the same as skippable.
S1.4, R3.2, R3.1, R2.2, S2.2, S3.1 and S3.2 alone account for nearly six marks in ten. Securing those seven before polishing the tail is the highest-return revision order available.
The new structure splits assessment three ways: Paper 1A (multiple choice), Paper 1B (data-based / experimental) and Paper 2 (extended response). This chart shows the marks each theme carries on each paper — Paper 2 is where almost all the depth (and synthesis) lives.
Paper 2 alone carries more marks than 1A and 1B combined, and it is the majority paper for five of the six themes (R1 highest at 66%). It is the paper that decides grades — and, as the next section shows, the paper that blends topics the hardest.
S1 Models of particulate matter takes 68.6 of Paper 1B's 175 marks — 39% of the entire data paper — and S1.4 The mole alone accounts for 49.6 of them. Add R3 (38.2 marks, mostly titrations and redox) and just two themes own three-fifths of Paper 1B.
S2 Models of bonding (61% of its marks) and R1 What drives reactions (66%) are the most Paper-2-weighted themes — Lewis structures, VSEPR, intermolecular forces, Hess and Born–Haber cycles need working space that multiple choice cannot give.
There is no "Paper 1A-only" or "Paper 2-only" theme you can revise in isolation — the same content is re-tested in three different formats. Eight sub-topics do sit out Paper 1B (organic, ideal gases, energy cycles and the ionic model among them), because they are hard to set as a lab-data task.
The redesigned exams were deliberately built to blend themes inside a single question. You are no longer answering "an equilibrium question" or "an organic question" — you are answering one long question that opens with a mole calculation, moves through energetics and kinetics, and finishes with a mechanism drawn in curly arrows. Revising topics in isolation is no longer enough: on Chemistry HL the marks live in the connections, and the effect is stronger here than in any other science we have analysed.
How we count this. "Multi-topic" is not a judgement call about how synthesis-like a question feels. It means exactly one thing: the question is tagged against two or more distinct syllabus topics in Photon Academy's own per-question tagging of every paper. "Cross-theme" is the stricter subset — the tagged topics come from two or more different themes (Structure vs Reactivity), so every cross-theme question is also a multi-topic question.
Paper 2 is not merely multi-topic-heavy — it is almost entirely multi-topic. Only three of its 32 questions stay inside a single topic, and those three carry 4% of the paper. A single extended-response item can open with limiting reactant and molar gas volume, pivot into a rate curve comparing strong and weak acids, and close on a Born–Haber cycle and a lattice-enthalpy trend — all chained, so an early slip in stoichiometry silently sinks the energetics marks that follow. The examiners reward students who can connect themes, not just recall them.
| R3 + S3 Mechanisms + Classification of matterOrganic mechanisms and redox tied to functional groups, nomenclature, isomerism and periodic trends. | ×19 |
| R2 + S1 How much / fast / far + Particulate matterRates, yields and equilibria resting on mole calculations, concentration and gas volumes. | ×17 |
| R2 + R3 How much / fast / far + MechanismsRate laws and equilibrium positions linked to acid–base and redox chemistry. | ×17 |
| R1 + R2 What drives reactions + How much / fast / farEnthalpy, entropy and Gibbs energy joined to rate, extent and the equilibrium constant. | ×14 |
| R1 + R3 What drives reactions + MechanismsEnergetics feeding electrochemistry — Gibbs energy and cell potential, enthalpy of neutralisation. | ×13 |
| S2 + S3 Bonding & structure + Classification of matterLewis structures, VSEPR and intermolecular forces explaining periodic trends and organic properties. | ×13 |
Concept lists paraphrased from our own tagging of the papers — not reproductions of exam wording.
Every one of the 248 questions rated for demand. The spread looks gentler than the mark distribution suggests — but that is because the hard questions are the long, multi-topic Paper 2 items above, so they carry far more marks each than their headcount implies.
Recall, single-step and "state / identify" items — mostly Paper 1A multiple choice and the opening parts of longer questions. Roughly a third of the question count, but a much smaller share of the marks. These are the marks you simply must not drop.
53% of questions need two or three linked steps — a mole calculation feeding an enthalpy, a structure feeding a property. This is where most candidates win or lose their grade, through accuracy and setting-out rather than exotic content.
Only 36 questions, but they are the long synthesis items that chain four or five themes together and carry a disproportionate share of the marks. Handling them is what separates a 6 from a 7.
Official grade boundaries for the new syllabus.
Because the redesigned course has only just had its first sittings, we are still gathering and verifying the official IB grade-boundary documents for Chemistry HL. Rather than publish estimated or fabricated numbers, we are leaving this section blank until we have confirmed data. Check back — or ask your IB coordinator for the official boundaries in the meantime.
Full IB-style predicted papers for the new Chemistry HL course — Paper 1A, 1B and 2 with markschemes — modelled on the synthesis patterns above.
Our tutors are currently writing predicted paper sets for the redesigned Chemistry HL course, built to mirror the cross-topic Paper 2 style this analysis uncovered. They are not published yet. In the meantime, the fastest way to prepare for a synthesis exam is targeted, tutor-led practice on the exact theme combinations that keep recurring.