Many elements have unequal numbers of neutrons and protons in their nucleus. An element's atomic weight refers to the total weight of neutrons, protons, and electrons. Atomic number describes the number of protons found in an atom. Some elements can have variants containing different numbers of neutrons but similar numbers of protons. We call these variants isotopes .
Carbon has two isotopes.
The isotope carbon-13 has 6 protons plus 7 neutrons. Carbon-14 is the rarest isotope of carbon containing 8 neutrons. Some isotopes are unstable and their nucleus tends to lose subatomic particles forming an element with a lower atomic mass. This process is known as radioactive decay . Metals are elements that usually conduct heat and electricity and are shiny.