Fundamental Particles

2026 Syllabus Objectives

By the end of this topic, you should be able to:

  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
  2. Recall and use the charge of each flavour of quark and understand that its respective antiquark has the opposite charge
  3. Recall that protons and neutrons are not fundamental particles and describe protons and neutrons in terms of their quark composition
  4. Understand that a hadron may be either a baryon (consisting of three quarks) or a meson (consisting of one quark and one antiquark)
  5. Describe the changes to quark composition that take place during β– and β+ decay
  6. Recall that electrons and neutrinos are fundamental particles called leptons

Main Content

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What Are Fundamental Particles?

Fundamental particles are the smallest building blocks of matter. They are particles that cannot be broken down into anything smaller. Think of them like the basic LEGO bricks that cannot be split apart – everything else is built from these basic pieces.

Not all particles are fundamental. For example, you might think atoms are fundamental, but they're not – atoms are made of protons, neutrons, and electrons. Even protons and neutrons are not fundamental – they are made of even smaller particles called quarks.

The Six Quarks

Quarks are one type of fundamental particle. There are six different types (or "flavours") of quarks:

  1. Up (symbol: u)
  2. Down (symbol: d)
  3. Strange (symbol: s)
  4. Charm (symbol: c)
  5. Top (symbol: t)
  6. Bottom (symbol: b)

Important fact: Quarks are never found alone in nature. They always stick together in groups of either two or three quarks.

Charges of Quarks

Each quark has an electric charge, but these charges are fractions (not whole numbers like you might be used to). The charge is measured in units of e, where e = 1.6 × 10⁻¹⁹ C (the charge of a single electron).

Here are the charges you need to remember:

QuarkSymbolCharge
Upu+⅔e
Downd-⅓e
Stranges-⅓e
Charmc+⅔e
Topt+⅔e
Bottomb-⅓e

Pattern to remember:

  • Three quarks have charge +⅔e: up, charm, and top
  • Three quarks have charge -⅓e: down, strange, and bottom

Antiquarks

Every quark has an antiparticle called an antiquark. Antiquarks are exactly the same as quarks except they have the opposite charge.

For example:

  • The anti-up quark (written as ū) has charge -⅔e (opposite of +⅔e)
  • The anti-down quark (written as đ) has charge +⅓e (opposite of -⅓e)

You don't need to memorize the antiquark charges separately – just remember that they're the opposite of the normal quark charges.

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