what are the chemical properties of heavy metals

A heavy metal is any one of a number of elements that exhibit metallic properties, which includes transition metals lanthanides actinides as well as the metalloids Arsenic and Antimony. Typically the term refers to elements of atomic number 21 or higher (e.g. Scandium or above) The term heavy metal chiefly arose with discussions of pollutants discharged to the environment in the form of air, water or soil contaminants. While many heavy metals have considerable toxicity, others are considered not deemed to possess significant toxic properties, and, in fact, several of these elements including zinc, iron, copper,chromium and cobalt are necessary for metabolic function for a large class of organisms.