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Six elements near the end of periods (rows) 4 to 7 sometimes considered metalloids are treated here as metals: they are germanium (Ge), arsenic (As), selenium (Se), antimony (Sb), tellurium (Te), and astatine (At). It illustrates the lack of agreement surrounding the concept, with the possible exception of mercury, lead and bismuth. two based on density, three on atomic weight, two on atomic number, and three on chemical behaviour. This table shows the number of heavy metal criteria met by each metal, out of the ten criteria listed in this section i.e.

6 Properties compared with light metalsĭefinitions Heat map of heavy metals in the periodic table.5 Formation, abundance, occurrence, and extraction.4.2 Nutritionally essential heavy metals.1.1 List of heavy metals based on density.They are used in, for example, golf clubs, cars, antiseptics, self-cleaning ovens, plastics, solar panels, mobile phones, and particle accelerators. Heavy metals are relatively scarce in the Earth's crust but are present in many aspects of modern life. While it is relatively easy to distinguish a heavy metal such as tungsten from a lighter metal such as sodium, a few heavy metals, such as zinc, mercury, and lead, have some of the characteristics of lighter metals, and, lighter metals such as beryllium, scandium, and titanium, have some of the characteristics of heavier metals. As well as being relatively dense, heavy metals tend to be less reactive than lighter metals and have far fewer soluble sulfides and hydroxides. Physical and chemical characterisations of heavy metals need to be treated with caution, as the metals involved are not always consistently defined. Potential sources of heavy metal poisoning include mining, tailings, industrial waste, agricultural runoff, occupational exposure, paints and treated timber. Other heavy metals, such as cadmium, mercury, and lead, are highly poisonous. Some heavy metals are either essential nutrients (typically iron, cobalt, and zinc), or relatively harmless (such as ruthenium, silver, and indium), but can be toxic in larger amounts or certain forms. From 1809 onward, light metals, such as magnesium, aluminium, and titanium, were discovered, as well as less well-known heavy metals including gallium, thallium, and hafnium. The earliest known metals-common metals such as iron, copper, and tin, and precious metals such as silver, gold, and platinum-are heavy metals. A density of more than 5 g/cm 3 is sometimes quoted as a commonly used criterion and is used in the body of this article. Despite this lack of agreement, the term (plural or singular) is widely used in science. The definitions surveyed in this article encompass up to 96 out of the 118 known chemical elements only mercury, lead and bismuth meet all of them. More specific definitions have been published, but none of these have been widely accepted. In metallurgy, for example, a heavy metal may be defined on the basis of density, whereas in physics the distinguishing criterion might be atomic number, while a chemist would likely be more concerned with chemical behaviour. The criteria used, and whether metalloids are included, vary depending on the author and context. Heavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers.

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