ABSTRACT

The chemical elements are commonly classified into metals, metalloids, and non-metals. There are differences of opinion on which elements should be called “heavy metals” as well as metalloids. Metalloids like arsenic and antimony, non-metals like selenium, and light metals like aluminum and beryllium are often included as heavy metals in many publications, creating confusion. Various criteria such as density, atomic weight, or relative atomic mass, or even atomic number, have been used to designate heavy metals without consistency. The term “trace metals” is also loosely used. To do away with these inconsistencies, it was proposed to classify the metals into Class A, Class B, and borderline elements. However, it is difficult to discontinue the use of the term heavy metals because of its extensive use in scientific literature, policy, and regulations. Nevertheless, several authors opposed the use of the term heavy metals, which could be simply called metals or metalloids, as the case may be. A recent scheme has suggested the use of heavy metals as a generic term to be applied to elements that satisfy the three criteria of being a metal, having an atomic number of greater than 20, and a density greater than 5 g cm–3.