Fundamental Particles

Objectives

Lesson outcomes

Recall the six flavours of quark and use their charges in particle descriptions.
Describe protons and neutrons in terms of their quark composition.
Classify hadrons as baryons or mesons from their quark structure.
Describe quark changes in beta-minus and beta-plus decay and identify leptons.

Syllabus

CIE 9702 syllabus points

6 linked

11.2.1 understand that a quark is a fundamental particle and that there are six flavours (types) of quark: up, down, strange, charm, top and bottom
11.2.2 recall and use the charge of each flavour of quark and understand that its respective antiquark has the opposite charge (no knowledge of any other properties of quarks is required)
11.2.3 recall that protons and neutrons are not fundamental particles and describe protons and neutrons in terms of their quark composition
11.2.4 understand that a hadron may be either a baryon (consisting of three quarks) or a meson (consisting of one quark and one antiquark)
11.2.5 describe the changes to quark composition that take place during β – and β+ decay
11.2.6 recall that electrons and neutrinos are fundamental particles called leptons

Lesson Notes

Student guidance and lesson notes

Overview

This lesson introduces the particle model used at AS level. You should be able to identify quarks and leptons as fundamental particles, describe protons and neutrons using quark composition, and use quark changes to explain beta decay.

What You Need to Know

A quark is a fundamental particle. The six quark flavours are up, down, strange, charm, top, and bottom.
Up, charm, and top quarks have charge +2/3 e. Down, strange, and bottom quarks have charge -1/3 e.
Each antiquark has the opposite charge to its matching quark.
Protons and neutrons are not fundamental particles. A proton is uud; a neutron is udd.
Hadrons are particles made from quarks. Baryons contain three quarks, while mesons contain one quark and one antiquark.
In beta-minus decay, a down quark changes into an up quark. In beta-plus decay, an up quark changes into a down quark.
Electrons and neutrinos are fundamental particles called leptons.

How to Work Through It

Start by listing the quark flavours and grouping them by charge.
Build the proton and neutron from up and down quarks, then check the total charge.
Classify examples as baryons, mesons, leptons, or not enough information.
Link beta decay back to the previous lesson by identifying which quark changes and which lepton is emitted.

Check Your Understanding

What is the total charge of a proton from its uud composition?
Why is a neutron not a fundamental particle?
What is the difference between a baryon and a meson?
Which quark change occurs in beta-minus decay?

Common Mistakes

Calling protons and neutrons fundamental even though they are made from quarks.
Mixing up the charges of up and down quarks.
Treating all hadrons as baryons and forgetting mesons.
Describing beta decay only at the nuclear level without the quark-level change.

Next Steps

Practise using quark charges to check particle charge.
Use the revision lesson to connect atomic structure, decay equations, and particle classification.