Fundamental particles

In our story so far we've seen that everything seems to be made of protons, electrons and neutrons, which are bundled together to form atoms. The number of protons and electrons in an atom determines what element the atom forms. For example, an atom of copper contains twenty nine protons and twenty nine electrons.

The idea that atoms were made of protons, electrons and neutrons was established early in the 20th century. Since then we've found that reality is more complicated. For example:

• Protons and neutrons seem to be made of even smaller particles called quarks.
• While protons, electrons and neutrons seems to last for ever (the ones in your body were made in the big bang thirteen billion years ago),  there are particles that play a role in holding atoms together that are only last for about a million million million millionth of a second.

It might even be possible that the particles we know about today can be broken down into even smaller units, and we just haven't yet been able to build experimental equipment that is powerful enough to do it.
However, to illustrate the principles of quantum theory we can ignore most of the other fundamental particles that have been found, and concentrate mainly on protons and electrons. There is one other important particle, called a photon, which is actually a particle of light. We will get to know more about photons later.

NEXT LESSON: protons and electrons in atoms