MYP Chemistry: Subatomic Particles & the Atom — Common Questions Answered

Subatomic particles are the three components that make up an atom: protons and neutrons, which sit in the nucleus, and electrons, which occupy shells around it. Protons carry a positive charge, electrons a negative charge, and neutrons carry no charge at all.

Protons are positive, sit in the nucleus, and their count fixes which element an atom is. Neutrons are neutral, also in the nucleus, and add mass without changing charge. Electrons are negative, far lighter, and orbit in shells — they're what actually determines an atom's chemical bonding.

Subtract the atomic number from the mass number: neutrons = mass number − atomic number. The atomic number tells you the proton count, and since protons and electrons match in a neutral atom, this one subtraction gives you the missing piece.

Atomic number (bottom-left on notation, or Z) counts protons only and defines the element — it never changes for that element. Mass number (top-left, or A) counts protons plus neutrons together, so it varies between isotopes of the same element.

Isotopes are atoms of the same element — same proton number — with different numbers of neutrons, and therefore different mass numbers. They matter because they explain why elements have decimal atomic masses on the periodic table and underpin uses like carbon dating and medical tracers.

This topic is mostly assessed through MYP Criterion A: Knowing and Understanding — recalling particle properties, applying the neutron-calculation formula, and explaining isotopes in context. It also feeds Criterion C (Communicating) when you're asked to present atomic notation or diagrams clearly and Criterion D in investigations involving isotopes or radioactivity.

A 7 (top of the MYP 1-8 scale) needs more than correct recall — it needs accurate application in unfamiliar contexts and clear scientific explanations linking structure to properties. Nail the neutron formula cold, use correct terminology every time, and always justify your answer rather than just stating it.

The biggest one I see marking mock papers: mixing up mass number and atomic mass, then getting the neutron calculation wrong as a result. Close behind that — forgetting electrons equal protons only in a neutral atom, which trips students up the moment ions appear.

MYP atomic structure builds the foundation — particles, isotopes, basic notation. DP Chemistry, first examined under the current guide from 2025, builds directly on this with electron configuration, ionisation energy trends, and mass spectrometry calculations that assume you already know protons, neutrons and isotopes cold.

Conceptually it's one of the more approachable MYP Chemistry topics — the maths is simple subtraction, not algebra. Where students actually lose marks isn't the calculation itself; it's mixing up terminology (mass number vs atomic mass) or failing to explain isotopes properly in extended-response questions.

The most useful thing you can do isn't reteaching the science — it's quizzing your child on the neutron-calculation formula and asking them to explain isotopes out loud in their own words. If they can teach it back to you clearly, they've genuinely understood it, not just memorised it.

Look for materials organised by MYP criteria rather than generic chapter summaries, since your child is graded against Criteria A-D, not a percentage score. On RevisionPrep, the Revision Notes and Topical Worksheets for this unit are built around exactly those command terms and calculation types.