The IB Chemistry Syllabus (First Assessment 2025): Every Topic, SL and HL
By Michael Thompson · Education Specialist; 10 years teaching the IB at Bromsgrove School · Published 5 October 2026 · Updated 6 October 2026
The IB chemistry syllabus for first assessment in May 2025 is organised into two strands, Structure and Reactivity, each split into three sub-strands, giving 22 numbered topics in total. SL and HL students study the same 22 topics; one of them (R1.4) is taught at HL only, and most of the rest carry additional higher level material inside the topic. This page lists every topic with what it covers, marks which content is HL-only, and sets out the teaching hours and the paper weights. The full subject guide, with study advice and the IA, is at IB Chemistry.
Key Takeaways
- 22 topics in two strands: Structure (S1 to S3, 11 topics) covers models of matter and bonding; Reactivity (R1 to R3, 11 topics) covers what drives reactions, how much and how fast they happen, and their mechanisms.
- SL and HL share the same topic list: Only R1.4 Entropy and spontaneity is an HL-only topic; HL depth elsewhere comes from additional higher level content inside shared topics.
- 150 hours at SL, 240 at HL: Each level is syllabus content plus an experimental programme (110 + 40 at SL, 180 + 60 at HL), and the collaborative sciences project sits inside that experimental programme.
- Two papers and an IA, no Paper 3: Paper 1 (multiple choice plus data-based questions) is 36%, Paper 2 is 44% and the scientific investigation is 20%, with the same weights at SL and HL.
- Structure and Reactivity are linked: The guide ties the two strands together with linking questions ("structure determines reactivity, which in turn transforms structure"), and Reactivity topics such as energy cycles rely on bonding models from Structure 2.
In This Article
- The Syllabus at a Glance
- Structure 1 to 3: Every Topic
- Reactivity 1 to 3: Every Topic
- What Is HL-Only
- How the Syllabus Is Assessed
- Where to Find the Official Documents
- What to Do Next
1. The Syllabus at a Glance
The course replaced the old model (11 core topics, HL topics 12-21 and an option) with a two-strand framework built around one organising question: how do we understand matter, and how does it change? Structure answers the first half (particles, bonding, classification) and Reactivity answers the second (energetics, extent and rate, mechanisms). Each strand has three sub-strands, and each sub-strand holds between two and five numbered topics.
| Strand | Sub-strand | Topics |
|---|---|---|
| Structure | Structure 1 - Models of the particulate nature of matter | S1.1 to S1.5 |
| Structure | Structure 2 - Models of bonding and structure | S2.1 to S2.4 |
| Structure | Structure 3 - Classification of matter | S3.1 to S3.2 |
| Reactivity | Reactivity 1 - What drives chemical reactions? | R1.1 to R1.4 |
| Reactivity | Reactivity 2 - How much, how fast and how far? | R2.1 to R2.3 |
| Reactivity | Reactivity 3 - What are the mechanisms of chemical change? | R3.1 to R3.4 |
Teaching time is set per level and broken down by sub-strand and topic. The IB allocates 150 hours at SL (110 hours of syllabus content plus a 40-hour experimental programme) and 240 hours at HL (180 plus 60). The experimental programme includes the practical work, the collaborative sciences project and the time for the internal assessment. The guide also recommends hours for each sub-strand (SL/HL: Structure 1 17/21, Structure 2 20/30, Structure 3 16/31, Reactivity 1 12/22, Reactivity 2 21/31, Reactivity 3 24/45) and for each numbered topic, from 2 hours for S1.1 to 10 hours for S2.2 and R3.2 at SL.
The topic numbering is used on exam papers and in mark schemes, so it is worth learning. S1.4 means Structure strand, sub-strand 1, topic 4 (the mole); R2.3 means Reactivity strand, sub-strand 2, topic 3 (equilibrium).
2. Structure 1 to 3: Every Topic
The Structure strand builds the models the rest of the course depends on: what particles are, how they bond and how substances are classified. Each topic is listed with the level it is taught at.
| Topic | Name | What it covers | Level |
|---|---|---|---|
| S1.1 | Introduction to the particulate nature of matter | Elements, compounds and mixtures; states of matter and changes of state; the kinetic molecular theory | SL and HL |
| S1.2 | The nuclear atom | Protons, neutrons and electrons; isotopes and relative atomic mass; mass spectra (HL) | SL and HL |
| S1.3 | Electron configurations | Emission spectra, energy levels, sublevels and orbitals; writing electron configurations; ionisation energy trends (HL) | SL and HL |
| S1.4 | Counting particles by mass: the mole | The mole and Avogadro's constant; molar mass; empirical and molecular formulas; concentration | SL and HL |
| S1.5 | Ideal gases | The ideal gas model and its assumptions; the ideal gas equation; real gases and their deviations | SL and HL |
| S2.1 | The ionic model | Ion formation, ionic lattices, lattice enthalpy and the physical properties of ionic compounds | SL and HL |
| S2.2 | The covalent model | Covalent bonds, Lewis formulas, VSEPR and shapes, polarity, intermolecular forces, resonance and formal charge (HL) | SL and HL |
| S2.3 | The metallic model | The metallic bond, properties of metals, trends in melting point and conductivity; delocalised d-electrons in transition elements (HL) | SL and HL |
| S2.4 | From models to materials | The bonding triangle and the continuum between ionic, covalent and metallic bonding; alloys; addition polymers; condensation polymers (HL) | SL and HL |
| S3.1 | The periodic table: classification of elements | Groups, periods and blocks; periodicity in atomic radius, ionisation energy and electronegativity; transition elements (HL) | SL and HL |
| S3.2 | Functional groups: classification of organic compounds | Homologous series, IUPAC naming, functional groups, structural isomers; stereoisomerism (cis-trans and optical) and spectroscopic identification (HL) | SL and HL |
The HL additions inside S1.2, S1.3, S2.2, S2.3, S2.4, S3.1 and S3.2 are not separate topics. They appear under the same topic heading in the guide, marked as additional higher level content, which is why a shared topic list can still describe two courses of different length.
3. Reactivity 1 to 3: Every Topic
The Reactivity strand asks three questions in turn: what drives a reaction, how much and how fast it happens and how far it goes, and what the mechanism is. Each sub-strand is one of those questions.
| Topic | Name | What it covers | Level |
|---|---|---|---|
| R1.1 | Measuring enthalpy changes | Exothermic and endothermic reactions, enthalpy change, calorimetry and specific heat capacity calculations | SL and HL |
| R1.2 | Energy cycles in reactions | Bond enthalpies and Hess's law; enthalpies of formation and combustion, and Born-Haber cycles (HL) | SL and HL |
| R1.3 | Energy from fuels | Combustion of fuels, incomplete combustion, fossil fuels, biofuels and fuel cells | SL and HL |
| R1.4 | Entropy and spontaneity | Entropy, Gibbs energy and the conditions for a spontaneous reaction, including the link to equilibrium | HL only |
| R2.1 | How much? The amount of chemical change | Reacting masses and volumes, limiting reactants, percentage yield and atom economy | SL and HL |
| R2.2 | How fast? The rate of chemical change | Rate of reaction, collision theory, factors affecting rate, catalysts; rate expressions, order and the Arrhenius equation (HL) | SL and HL |
| R2.3 | How far? The extent of chemical change | Dynamic equilibrium, the equilibrium constant and Le Chatelier's principle; equilibrium calculations and the link to Gibbs energy (HL) | SL and HL |
| R3.1 | Proton transfer reactions | Bronsted-Lowry acids and bases, conjugate pairs, pH and Kw, strong and weak acids, neutralisation and strong acid-strong base pH curves; pKa, salt hydrolysis, indicators, buffers and weak acid or base pH curves (HL) | SL and HL |
| R3.2 | Electron transfer reactions | Oxidation states, redox equations, voltaic and electrolytic cells; standard electrode potentials and electrolysis of aqueous solutions (HL) | SL and HL |
| R3.3 | Electron sharing reactions | Radicals, homolytic fission and radical substitution in alkanes | SL and HL |
| R3.4 | Electron-pair sharing reactions | Nucleophiles and electrophiles, nucleophilic substitution, electrophilic addition, Lewis acids and bases, coordination compounds and mechanisms (HL) | SL and HL |
Read the two tables together rather than in order. R1.2 (energy cycles) needs the lattice enthalpy idea from S2.1, R2.3 (equilibrium) in its HL form uses the Gibbs energy of R1.4, and R3.4 leans on the shapes and polarity of S2.2. The IB chemistry subject guide explains why the strands are meant to be taught in parallel.
4. What Is HL-Only
One topic is taught at HL only: R1.4 Entropy and spontaneity. Everything else in the list is studied at both levels, with HL students covering additional higher level content inside 13 of the 21 shared topics.
- S1.2 - mass spectra and isotopic composition.
- S1.3 - the convergence limit of the emission spectrum and successive ionisation energy data.
- S2.2 - formal charge, resonance and expanded octets; sigma and pi bonding; hybridisation.
- S2.3 - delocalised d-electrons in transition elements.
- S2.4 - condensation polymers.
- S3.1 - transition elements, oxidation states and coloured complexes.
- S3.2 - stereoisomerism (cis-trans and optical), and mass spectrometry, infrared and proton NMR for identifying compounds.
- R1.2 - standard enthalpies of formation and combustion in Hess's law calculations, and Born-Haber cycles.
- R2.2 - rate expressions, order of reaction, rate constants and the Arrhenius equation.
- R2.3 - equilibrium calculations and the relationship between the equilibrium constant and Gibbs energy.
- R3.1 - pKa, pKb, buffer solutions, salt hydrolysis and titration curves.
- R3.2 - standard electrode potentials, the electrochemical series and electrolysis of aqueous solutions.
- R3.4 - Lewis acids and bases, coordination bonds and complex ions, SN1 and SN2 mechanisms, the mechanism of electrophilic addition (carbocation stability) and electrophilic substitution of benzene.
If you are choosing between SL and HL, the practical difference is depth rather than breadth: the HL student sits longer papers on more demanding versions of the same topics, plus the HL-only topic above. The SL versus HL comparison in the subject guide goes through what that means for workload.
5. How the Syllabus Is Assessed
External assessment is two written papers, and there is no Paper 3 in the 2025 course. Internal assessment is a single scientific investigation. The weights are the same at SL and HL; the difference is the length of the papers.
| Component | What it contains | SL | HL | Weight |
|---|---|---|---|---|
| Paper 1 | Paper 1A multiple choice plus Paper 1B data-based questions | 1 hour 30 minutes | 2 hours | 36% |
| Paper 2 | Short-answer and extended-response questions across the syllabus | 1 hour 30 minutes | 2 hours 30 minutes | 44% |
| Internal assessment | The scientific investigation, written up and marked by the teacher, moderated by the IB | 10 hours | 10 hours | 20% |
Paper 1B is the part of the structure that most often surprises students: it is sat in the same sitting as the multiple choice and asks data-based questions that draw on the experimental skills in the guide, so the practical programme is examined and not just completed. A clean copy of the data booklet is provided for every paper, Paper 1A included, and calculators are permitted throughout. The investigation is marked on four criteria, each out of six: research design, data analysis, conclusion and evaluation. The IB chemistry IA guide covers how to plan one.
6. Where to Find the Official Documents
The topic list on this page follows the IB's Chemistry guide for first assessment 2025, which teachers access through the IB programme resource centre. The public summary of the course is on the IB's Diploma Programme chemistry page, which links to the chemistry subject brief with the syllabus outline, teaching hours and assessment outline.
The data booklet is a separate IB publication from the guide. It holds the constants, formulae, the periodic table and the tables of values you are given in the examination, and it is updated with the syllabus. Our IB chemistry data booklet guide explains what is in it and how to use it in the papers.
7. What to Do Next
Use the two topic tables as a checklist: tick each topic once you have notes, questions done and a weak area identified for it. For the course as a whole, including study strategies and university routes, read the full IB Chemistry guide. If you are planning your investigation, start with the IB chemistry IA guide; if you are targeting the top grade, how to get a 7 in IB Chemistry sets out what separates a 6 from a 7. A draft investigation can be checked against the four criteria with the Chemistry HL IA grader.
FAQ
How many topics are in the IB chemistry syllabus?
There are 22 numbered topics: 11 in the Structure strand (S1.1 to S3.2) and 11 in the Reactivity strand (R1.1 to R3.4). SL and HL share the same list; only R1.4 is taught at HL only.
Is there a Paper 3 in IB Chemistry?
No. The course for first assessment 2025 has Paper 1 (1A multiple choice and 1B data-based questions, 36%), Paper 2 (44%) and the internal assessment (20%) at both SL and HL.
What is HL-only in IB Chemistry?
One whole topic, R1.4 Entropy and spontaneity, plus additional higher level content inside 13 shared topics, such as rate expressions, buffers, electrode potentials, Born-Haber cycles, stereoisomerism, spectroscopy and organic mechanisms.
How many teaching hours is IB Chemistry?
150 hours at SL (110 hours of syllabus content plus a 40-hour experimental programme) and 240 hours at HL (180 plus 60). The guide also recommends hours for each sub-strand and each numbered topic.
When did the current IB chemistry syllabus start?
First teaching was August 2023 and first assessment May 2025. Students examined in November 2024 or earlier sat the previous course (11 core topics, HL topics 12-21 and one option).
References
- Diploma Programme chemistry - International Baccalaureate - https://www.ibo.org/programmes/diploma-programme/curriculum/sciences/chemistry/
- Diploma Programme Subject Brief - Sciences: Chemistry, first assessment 2025 (International Baccalaureate Organization 2022) - https://www.ibo.org/globalassets/new-structure/recognition/pdfs/dp_sciences_chemistry_subject-brief_jan_2022_e.pdf