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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 reaction with fatty acids, e.g., aluminum, lead, cobalt." This definition must have been culled from a book about soaps, but clearly is not a useful definition in any other field.Turning to regular dictionaries (as opposed to chemical dictionaries): Webster (3) gives "A metal of high specific gravity; esp: a metal having a specific gravity of 5.0 or over."All the metals that I think of as heavy metals have densities above 5 g/cm 3 , while no metals with densities below 5 have heavy metal chemistry. This supports Webster's definition, but it is deceptive. Being a heavy metal has little to do with density, but rather concerns chemical properties.The metals that I have seen referred to as heavy metals comprise a block of all the metals in Groups 3 to 16 that are in periods 4 and greater. This seems to be a definition that should be generally useful. It may also be stated as the transition and post-transition metals. These acquired the name heavy metals because they all have high densities, but the usefulness of the term is related to their chemistry, not their density. It is not necessary to decide whether semimetals should be included as heavy metals, which is fortunate, since it is unlikely that any decision would be generally agreeable.The definition in bold type above should serve the needs of most chemists and some others who use the term. When it refers to a musical genre, the user is unlikely to be concerned about its chemical meaning.

Chemistry existed before there were laboratories, before there were humans, before there was life. Chemistry is the combination of principles and facts that caused the formation of the earth and its layering, that governs the ecosystem, and that underlie the properties of materials and of living organisms. Duplicating what we chemists do in our laboratories (or what chemists of earlier generations used to do) does not enhance students' understanding of chemistry's centrality, but makes chemistry an irrelevance.Laboratory classes do not help students to understand how chemical principles affect their universe. If labs are cleverly arranged and courageously taught, they can help in promoting interpretation and design of experiment but they are not useful in learning other aspects of chemistry. Interpretation and design of experiment is effectively taught using computer simulations (1), avoiding the great expense and frustration of a lab. Non-majors have no use for the manipulative skills that they may learn in a chemistry laboratory.For research on the effectiveness and usefulness of laboratory instruction, we may look to McKeachie's reviews of laboratory classes in science (2). Several studies showed that laboratory work made no significant difference in tests of information, practical application, scientific attitude, or laboratory performance. McKeachie concludes, "While reviews of research on laboratory teaching find that laboratory courses are effective in improving skills in handling apparatus or in visual-motor skills, laboratories are not very effective in teaching scientific method."However, McKeachie goes on to cite other studies that show "that the effectiveness of the laboratory depends on the manner in which the work is taught." Problem-solving methods are superior to more conventional systems in teaching to "apply principles of physics in interpreting phenomena" and in developing ability "to design an experiment." I do not believe that these skills are useful enough to non-majors that they should be required to take a lab course, or that we should provide it in preference to the other teaching for which time and resources could be used. If it is held that we should, then McKeachie's findings, which can be assumed to apply also to chemistry, support the lab-centered curriculum and the inquiry approach in specifically meeting these two objectives. However, at least one of them and probably both of them can be met by computer simulations.It is often urged that chemistry is a laboratory science, and that students therefore need a hands-on laboratory experience. Whether this follows depends on the students' reasons for studying chemistry. The non-major presumably studies chemistry in order to gain a better understanding of the universe, the earth, its ecosystem, and the mechanisms of life. The available evidence fails to show that this is enhanced by hands-on laboratory instruction. Honesty should demand such evidence before students are compelled to such instruction.Some students would profit by understa...

Exercises in d = m/v fail to teach the concept of density as the denseness with which mass is packed. This paper presents non-mathematical illustrations of the concept of density.

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