What Is a "Heavy Metal"?
No TL;DR found
Abstract
I asked this question of my introductory chemistry teacher over 50 years ago. He replied rather hesitantly, "A metal that behaves in a heavy metal manner." A vague term requires a vague definition, but just what is a "heavy metal manner"?In my day job I routinely conducted a test for heavy metals, which was and is described (1) as a test for "metallic impurities that are colored by sulfide ion". It may mean different things to different people, but as I have used, heard, and interpreted the term over the last half-century it refers to metals with insoluble sulfides and hydroxides, whose salts produce colored solutions in water, and whose complexes are usually colored.During a project to establish a pre-engineering chemistry curriculum, I found several references to heavy metals, together with two attempts to define them. I consulted a number of chemical dictionaries and found that most did not mention them at all. One (2) defined them as "metals of atomic weight greater than sodium that form soaps on reac...