Isotopes
Isotopes are atoms of the same element that differ in the number of neutrons. Isotopes have the same number of protons, but they have different atomic masses. For example, Carbon has three common isotopes. In the image below, you can see the carbon isotopes. Each has 6 protons. However, Carbon 12 will have 6 neutrons (the number after the dash is the atomic mass and therefore equals the protons + neutrons). Carbon 13 will have 7 neutrons and Carbon 14 will have 8 neutrons.