Structure: Models of the Particulate Nature of Matter
Structure 1
This is the topic that decides whether the rest of the course is arithmetic or guesswork. Every stoichiometry question, every gas-law problem, every 'explain the trend in ionisation energy' question comes back to the ideas here: particles have mass, occupy space, arrange themselves according to energy, and can be counted in bulk using the mole. Get sloppy with or with 4s-before-3d filling now, and it costs you marks in topics you haven't even met yet.
Overview — how the chapter fits together
Structure 1 builds the particle model from the ground up: what a particle is, what's inside it, how its electrons are arranged, how we count huge numbers of them (the mole), and — at HL — how a whole population of gas particles behaves statistically. Everything is really one idea repeated at different scales: particles + arrangement + energy = observable properties.
- SL and HL share Structure 1.1–1.4; Structure 1.5 (ideal gases) is HL-only content — if you're SL, skip that section entirely.
- Dalton's atomic theory (1.1) is the model examiners love to 'break' with modern evidence — isotopes, subatomic particles, mass spectrometry all exist to contradict specific Dalton postulates.
- The mole (1.4) is pure arithmetic once the four core equations are automatic — most lost marks here are unit or rounding errors, not conceptual ones.
The shape of the chapter
Command terms examiners actually use in this topic
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| Define | Give the precise, complete meaning of a term | AO1 | A description instead of the exact definition (e.g. 'atoms with different masses' instead of 'atoms of the same element with different numbers of neutrons') drops the mark. |
| Distinguish between | State the difference(s) between two things explicitly | AO2 | Two separate correct descriptions with no comparative word (whereas/but/unlike) usually scores zero — the contrast itself is the mark. |
| Deduce | Reach a conclusion using the data or reasoning given in the question | AO3 | Quoting a memorised fact instead of working from the given data (e.g. the isotopic abundances in the question) loses the method mark even if the final number is right. |
| Determine | Obtain a numerical answer, showing working | AO2 | Correct final answer with no working can lose the method mark; wrong answer with correct method still earns ecf (error carried forward) marks. |
| Sketch | Draw an approximate graph/diagram showing the important features | AO2 | Axes must be labelled and shape/intercepts correct even without a precise scale — an unlabelled axis loses a mark regardless of how accurate the curve is. |
Key point
Overview