Heavy metal (elements) in the context of "Bismuth"

Lead (/lɛd/ ) is a chemical element with the symbol Pb (from the Latin plumbum) and atomic number 82. It is a heavy metal, denser than most common materials. Lead is soft, malleable, and has a relatively low melting point. When freshly cut, it appears shiny gray with a bluish tint, but tarnishes to dull gray on exposure to air. Lead has the highest atomic number of any stable element, and three of its isotopes are endpoints of major nuclear decay chains of heavier elements.

Lead is a relatively unreactive post-transition metal. Its weak metallic character is shown by its amphoteric behavior: lead and lead oxides react with both acids and bases, and it tends to form covalent bonds. Lead compounds usually occur in the +2 oxidation state rather than the +4 state common in lighter members of the carbon group, with exceptions mostly limited to organolead compounds. Like the lighter members of the group, lead can bond with itself, forming chains and polyhedral structures.

Dark chocolate, also known as plain chocolate and black chocolate, is a form of chocolate made from cocoa solids, cocoa butter and sugar. It has a higher cocoa percentage than white chocolate and milk chocolate. Dark chocolate is valued for its health benefits, and for its reputation as a sophisticated choice of chocolate. Like milk and white chocolate, dark chocolate is used to make chocolate bars and to coat confectionery.

Dark chocolate gained much of its reputation in the late 20th century, as French chocolatiers worked to establish dark chocolate as preferred over milk chocolate in the French national palate. As this preference was exported to countries such as the United States, associated values of terroir, bean-to-bar chocolate making and gourmet chocolate followed. Because of the high cocoa percentage, dark chocolate can contain particularly high amounts of heavy metals such as lead and cadmium.