MYP Science: The Particle Model

Four ideas you must be able to use, not just recite:

1. Particles are always moving - even in solids, where they vibrate on the spot.
2. There's space between particles - more in gases, almost none in solids.
3. Forces hold particles together - strong in solids, weakest in gases.
4. Energy in means faster particle motion, which is what actually causes a change of state.

Most lost marks come from stopping at point 1 and never linking energy to behaviour.

A plasma state exists too, but MYP 1-3 doesn't require it - stick to these three unless your unit planner says otherwise.

Think of it as a zoom lens. In MYP 1-3, you're at low zoom: particles are just 'balls' that move and take up space. By MYP 4-5 and into DP, the zoom increases - particles become atoms, ions and molecules with internal structure, which is what lets you explain bonding, reactivity and chemical change rather than just melting and boiling.

Worked example - ice melting at 0°C:

1. Energy is added (heat from the room).
2. Particle vibration increases until forces holding the fixed pattern are overcome.
3. Particles gain enough freedom to slide past each other - it's now liquid.
4. Temperature doesn't rise during the melt itself - the energy is going into breaking the pattern, not increasing particle speed. This is the detail most MYP students miss when asked to 'explain' rather than just 'describe'.

The four MYP Sciences criteria, each marked on an 8-point achievement level scale per year: Criterion A - Knowing and understanding; Criterion B - Inquiring and designing; Criterion C - Processing and evaluating; Criterion D - Reflecting on the impacts of science. A particle model unit will most often show up under A and C.

Quick tip: Before you submit any particle model answer, check you haven't written 'the particles melt' or 'the particles expand.' Particles don't melt or expand - substances do, because the spaces between particles and their motion change. That single wording fix moves answers up a rubric band more often than any extra content would.

Worked example: A bottle of perfume opens in a corner of a room.

1. Particles start concentrated near the bottle.
2. Random particle motion and collisions cause them to spread in all directions.
3. Over minutes, concentration evens out across the room - diffusion is complete when it's uniform, not when particles stop moving.

Note: diffusion is faster in gases than liquids (more space, faster particles) and faster at higher temperatures - both good extension points for an 'explain' question.

Four steps for any particle model question:

1. Underline the command term and the context (e.g. 'melting wax', 'gas in a balloon').
2. Write one sentence stating the relevant part of the model.
3. Apply it directly - link cause (energy/heat) to effect (particle behaviour) to outcome (state or property).
4. Use exact terms: 'kinetic energy', 'forces between particles', 'spacing' - not 'stuff moves faster'.

In my experience marking Criterion A tasks, the students who lose a full achievement band almost never lack understanding - they lack the specific vocabulary the rubric descriptors are looking for. That's a fixable problem, not an ability problem.

3 things to check before your next assessed task:

1. Have I used 'particles' correctly, never saying the substance itself expands or melts?
2. Have I linked energy change to particle motion, not just described what's observed?
3. Have I answered the actual command term (describe vs explain vs compare)?

Running through these three catches most of the marks students otherwise leave on the table.

Students who can genuinely explain (not just describe) the particle model in MYP tend to find DP's kinetic theory and gas law calculations far less abstract later on.

If your child moves between an MYP school and a national-curriculum school mid-way through this topic, the content gap is small. The bigger adjustment is learning to write for timed, mark-scheme-based exam questions instead of criterion-based classroom tasks - worth practising deliberately before any transfer, not assuming it transfers automatically.

Three signs a resource is actually built for MYP, not just relabelled: it uses MYP command terms (describe, explain, discuss); it references the four assessment criteria by name; and it includes short-answer practice, not only multiple choice - because that's the format your child will actually be marked on in class.