How are atoms that have excess energy and are unstable referred to?

Atoms that have excess energy and are unstable are referred to as radioactive. Radioactivity is a phenomenon that occurs in certain isotopes of elements, where the nucleus of the atom is not stable due to an imbalance in the number of protons and neutrons. This instability leads the atom to release energy in the form of radiation as it seeks to reach a more stable state. This radiation can take various forms including alpha particles, beta particles, and gamma rays.

The term "radioactive" specifically describes the process of spontaneous decay that these unstable atoms undergo. As they release energy, they transform into different elements or isotopes, ultimately moving towards stability. Understanding this concept is crucial in radiation safety practices, as it relates directly to the handling and management of radioactive materials and the potential exposure to radiation they may present.