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IB Chemistry revision notes

Group 4 · Sciences · SL / HL

Structure 1 is the foundation of the whole course: what atoms are made of, how electrons are arranged, and how chemists count particles with the mole.

Course topics

Structure 1 · Models of the particulate nature of matter · Atoms, isotopes, electron configuration, the mole · 5 subtopics
Structure 2 · Models of bonding and structure · Ionic, covalent and metallic bonding, intermolecular forces · 4 subtopics
Structure 3 · Classification of matter · Periodic table trends, functional groups, nomenclature · 2 subtopics
Reactivity 1 · What drives chemical reactions? · Enthalpy, Hess's law, bond enthalpies, entropy (HL) · 4 subtopics
Reactivity 2 · How much, how fast and how far? · Stoichiometry, rates, equilibrium · 3 subtopics
Reactivity 3 · What are the mechanisms of chemical change? · Acids and bases, redox, electron sharing and pair reactions · 4 subtopics

Free lesson: Structure 1 · Models of the particulate nature of matter

Atomic number (Z): Number of protons. It defines the element
Mass number (A): Protons + neutrons
The mole: 6.02 × 10²³ particles (Avogadro's constant)

\[\text{neutrons}=A-Z\qquad n=\frac{m}{M}\]

\[A_r=\frac{\sum\left(\text{isotope mass}\times\text{abundance}\right)}{100}\]

Isotopes have the same number of protons but different numbers of neutrons. Same chemistry, different mass.
Electron configuration fills orbitals in order 1s 2s 2p 3s 3p 4s 3d. Exceptions to learn: Cr [Ar]3d⁵4s¹ and Cu [Ar]3d¹⁰4s¹.
Emission spectra: electrons fall to lower energy levels and give out light at fixed frequencies, so the lines are discrete.

Worked example

Chlorine is 75.8% ³⁵Cl and 24.2% ³⁷Cl. Calculate its relative atomic mass.

Multiply each mass by its abundance: 35 × 75.8 = 2653 and 37 × 24.2 = 895.4.
Add them: 2653 + 895.4 = 3548.4.
Divide by 100: Aᵣ = 35.48.
Check: the answer sits between 35 and 37, closer to 35 because that isotope is more common.

Common mistakes

Confusing atomic number with mass number.
Forgetting that 4s fills before 3d but empties first when ions form.
Using mass in kg instead of g in n = m / M.
Rounding Aᵣ too early.

Quick check

²³Na has Z = 11. How many neutrons does it have?

12. Neutrons = A − Z = 23 − 11 = 12.

What is the electron configuration of oxygen (Z = 8)?

1s² 2s² 2p⁴. 8 electrons: 2 in 1s, 2 in 2s, 4 in 2p.

How many moles are in 9.0 g of water (M = 18.02 g mol⁻¹)?

0.50 mol. n = 9.0 / 18.02 ≈ 0.50 mol.

Isotopes of the same element differ in their number of…

neutrons. Same protons (same element), different neutrons, so different mass numbers.

Practise this in the app. Interactive diagrams, quizzes, exam-style papers with mark schemes and a personal study planner. Open Chemistry in FortyFive →

FAQ

What topics are in IB Chemistry?

IB Chemistry (SL / HL) is organised into: Structure 1 · Models of the particulate nature of matter; Structure 2 · Models of bonding and structure; Structure 3 · Classification of matter; Reactivity 1 · What drives chemical reactions?; Reactivity 2 · How much, how fast and how far?; Reactivity 3 · What are the mechanisms of chemical change?.

Are these IB Chemistry notes free?

Yes. The topic pages, key terms and the first lesson are free. The full lessons, interactive diagrams and exam-style practice papers with mark schemes are in the FortyFive app, which you can start for free.

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