2.  Atomic Number

3.  Protons + Neutrons = Atomic Mass

4.  An Atom of an Element that has the same number of protons as another atom of the same element but a different number of neutrons.

6. Isotopes of an element have the same chemical properties.

9. Na - 23

10. Average of all the isotopes of that element

11.  May make the element have a different radioactivity.  Radioactivity is the release of energy and matter that results from changes in the nucleus of an atom  An isotope that is radioactive is called a radioisotope or radionuclide. The

12. Often called Radioisotopes How does this happen? An additional neutron or two may upset the nucleus and cause the atom to become unstable. In an unstable atom, the nucleus changes by giving off a neutron to get back to a balanced state. As the unstable nucleus changes, it gives off radiation and is said to be radioactive.

13.  Are Radioisotopes  Have unstable nuclei and are radioactive.

14. Have isotopes with a stable nucleus And Most have at least one radioisotope with an unstable nucleus.