Marks-weighted analysis of 191 questions across 525 marks from 15 IB Chemistry SL papers. The headline finding: 69.3% of all marks come from questions tagged with two or more distinct syllabus topics — the redesigned Structure-and-Reactivity course rewards students who connect ideas, not those who revise them in isolation.
Share of total marks across the six IB Chemistry themes. Structure 1 (models of particulate matter) and Reactivity 3 (mechanisms of chemical change) are effectively tied at the top — together they take just over half of every exam.
S1 leads at 25.9% and R3 sits right behind at 25.0% — a gap of fewer than five marks across the whole dataset. Below them the marks thin out fast, but even the smallest theme (R1, 8.5%) is worth roughly 45 marks: nothing here is safe to skip.
All 21 examined sub-topics ranked by % of total marks, colour-coded by theme (cool = Structure, warm = Reactivity). This is the chart that matters most for revision planning: the top five sub-topics alone carry half the marks.
The mole and stoichiometry (S1.4) is the single biggest sub-topic at 13.9% — and it is quietly load-bearing everywhere else, because a redox, equilibrium or enthalpy question usually opens with a calculation before it gets to the chemistry.
Marks per theme split across the three papers. Paper 2 carries the heaviest load in every theme — and, as the next section shows, that is where the topics get fused together.
Paper 1A = multiple choice · Paper 1B = data-based / experimental · Paper 2 = extended response. Values are marks attributed to each theme after multi-topic questions are split among their tags. Note how lopsided Paper 1B is: 53.8 of its marks land in Structure 1, and 44.3 of those come from the mole and stoichiometry alone — the data paper is, in practice, a quantitative-chemistry paper.
The redesigned 2025 exams were built to blend Structure and Reactivity inside a single question. A Paper 2 part now routinely runs from a mole calculation into a redox half-equation, from bonding and shape into intermolecular forces and boiling points, from a functional group into a mechanism and then into atom economy — all in one train of reasoning. Revising each topic in a silo is no longer enough: more than two-thirds of all marks sit in questions that draw on two or more distinct syllabus topics.
How we count this. "Multi-topic" is not a subjective judgement 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 of those — the tagged topics come from two or more different themes (Structure vs Reactivity) — so every cross-theme question is also a multi-topic question.
| Themes fused | Times seen | What that means in a question |
|---|---|---|
| R3 + S1 Mechanisms of change + Particulate matter | 13 | Redox, acid–base or organic mechanism work that first demands moles, concentration, electron configuration or a balanced equation before the chemistry can start. |
| R2 + S1 How much / fast / far + Particulate matter | 11 | Yield, limiting reactant, rate or equilibrium questions built on top of stoichiometry and gas-law or concentration calculations. |
| R3 + S3 Mechanisms of change + Classification of matter | 11 | Organic mechanisms tied to functional groups, naming and isomerism, or periodic trends driving acid–base and redox behaviour. |
| S2 + S3 Bonding & structure + Classification of matter | 9 | Lewis structures, shape and polarity used to explain periodic trends, organic families and the physical properties that follow from them. |
| S1 + S2 Particulate matter + Bonding & structure | 9 | Electron configuration and ionization data feeding into ionic-versus-covalent character, VSEPR geometry and intermolecular forces. |
| R3 + S2 Mechanisms of change + Bonding & structure | 9 | Bond polarity and structure used to predict where a nucleophile attacks, how a radical forms, or why one acid is stronger than another. |
Strong versus weak acid pH and conjugate pairs, then oxidation states, then functional groups and isomerism, then catalysis, then free-radical substitution, then bond enthalpy against a Hess cycle — closing on atom economy.
Catalysis and activation energy, then constructing an oxidation half-equation and combining it into the overall redox equation, then ionic versus covalent bonding, then the Lewis formula and VSEPR geometry of the nitrate ion.
Identifying an addition-polymer monomer and its polymer properties, then naming and isomerism, then oxidation and reduction of an aldehyde, then electrophilic addition of bromine, then a London-forces boiling-point trend, then enthalpy from bond enthalpies.
IUPAC naming and isomerism, then percentage by mass, then a curly-arrow nucleophilic substitution mechanism, then homolytic versus heterolytic fission, then collision theory.
Electron configuration, then Lewis structure, VSEPR and polarity, then a balanced equation with state symbols, then oxidation states, then acid attack on a carbonate, then hydrogen bonding — ending on covalent-network versus polymer melting points.
Yield and atom economy, then an energy profile with and without a catalyst, then Maxwell–Boltzmann distributions and activation energy, then Le Châtelier, then addition polymerization, then functional groups and oxidation, then a weak-acid titration curve.
Relative atomic mass from isotopic abundance, then ionization energy and shielding, then ionic versus covalent bonding, then neutralization stoichiometry, then amphoterism, then redox displacement and the reactivity series.
An ionization-energy trend read across a period, then the periodicity that explains it, then the acid–base character of the corresponding oxides — periodic-table reasoning carried all the way into reaction behaviour.
How the 191 questions break down by accessibility. Most of the paper is genuinely attemptable — but the multi-topic questions above are where the "hard" band clusters.
Over a third of questions are accessible marks — recall, a single substitution, reading a value off a table or graph. These are non-negotiable and should be banked in full.
The core of every paper. Two- and three-step reasoning within a topic — reliable marks for students who have drilled past papers.
The demanding band, dominated by the cross-topic synthesis questions above. This is exactly where connecting Structure to Reactivity earns the grade.
Official grade boundaries for the new 2025 Chemistry syllabus.
With only two new-syllabus sittings (May 2025 and November 2025) so far, we are gathering the official IB grade boundary documents before publishing a table. We will not print estimated or fabricated numbers here — as soon as verified boundaries are available for the redesigned Chemistry SL course, they will appear in this section.
Full IB-style predicted papers for the new Chemistry SL syllabus are in development — modelled directly on the cross-topic patterns you see above.
Because the syllabus is new, we are writing Chemistry SL predicted papers from scratch — Paper 1A, 1B and 2 in exam style, deliberately built around the Structure-into-Reactivity synthesis that defines the redesigned course. They are not published yet. In the meantime, our tutors work through real new-syllabus questions with students and drill the exact theme pairings that carry the marks.