heavy metal

     You may encounter the phrase "heavy metal" and wonder where the music is. I don't know what scientific "heavy metal" has to do with musical "heavy metal", but the scientific version of "heavy metal" refers to the atomic weight of a metal or element. The "atomic weight" of an element means the weight of a single atom, compared to the weight of a single atom of another element.
     You may be familiar with the symbol for an atom, which is often used in pop culture.
      The "heavy metals" are some of the substances that are toxic to people and the environment--lead and  plutonium, for example.
    If you want to know more, you can look for the "periodic table of the elements", or "atoms" or "chemistry", in Wikipedia or on a science or chemistry site.