Nuclear radiation

Structure of an atom

Inside every atom there are even smaller particles: protons, electrons and neutrons.

These particles can be found in particular places inside the atom:

Helium atom with 2 neutrons and 2 protons in the centre and 2 electrons on the outer edgeHelium atom with two neutrons and two protons in the nucleus and two electrons in orbit

Although the word 'atom' comes from the Greek for indivisible, we now know that atoms are not the smallest particles of matter. Atoms are made from smaller subatomic particles.

At the centre of an atom is a nucleus containing protons and neutrons. Electrons are arranged around the nucleus in energy levels or shells.

Both protons and electrons have an electrical charge. Both have the same size of electrical charge, but the proton is positive and the electron negative. The neutron is neutral.

The electrical charge of particles

The electrical charge of particles
ParticleRelative charge
proton+1
neutron0
electron-1

The total number of electrons in an atom is always the same as the number of protons in the nucleus. This means atoms have no overall electrical charge.