Introduction to an Atom

Atoms are made up of three key ingredients: protons, neutrons and electrons. The nucleus is the center of the atom, made of just protons and neutrons, and electrons orbit the nucleus.

Nuclear model of atom. Neutron and proton particles in the center of model create nucleus. Smaller electron particles orbit around the nucleus.

Figure 1: Atomic structure and particles within it.

A nucleus with a specific number of neutrons and protons is called a nuclide. Nuclides that are made up of a balanced mix of protons and neutrons are stable, meaning they are very hard to break down. Adding or removing neutrons and protons to a stable nuclide can make it less stable.

When an unstable nuclide breaks apart it emits radiation. We call this process radioactive decay.