Heavy metals only mercury, lead and bismuth meet all of them. Despite this lack of agreement, the term (plural or singular) is widely used in science. A density of more than 5 g/cm is sometimes quoted as a commonly used criterion and is used in the body of this article. The earliest known metals—common metals such as iron, copper, and tin, and precious metals such as silver, gold, and platinum—are heavy metals. From 1809 onwards, light metals, such as magnesium, aluminium, and titanium, were discovered, as well as less well-known heavy metals including gallium, thallium, and hafnium. Some heavy metals are either
Group 6 element The metals form compounds in different oxidation states: chromium forms compounds in all states from −2 to +6: disodium pentacarbonylchromate, disodium decacarbonyldichromate, bis(benzene)chromium, tripotassium pentanitrocyanochromate, chromium(II) chloride, chromium(III) oxide, chromium(IV) chloride, potassium tetraperoxochromate(V), and chromium(VI) dichloride dioxide; the same is also true for molybdenum and tungsten, but the stability of the +6 state grows down the group. Depending on oxidation states, the compounds are basic, amphoteric, or acidic; the acidity grows with the oxidation state of the metal. Tungsten has no known biological role in the human body. Seaborgium's high radioactivity would make it a toxic element, due to radiation