why are lead and mercury called heavy metals
Heavy metals Heavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers. The criteria used, and whether metalloids are included, vary depending on the author and context. 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. More specific definitions have been published, but none of these have been widely accepted. 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. Despite this lack of agreement, the term (plural or singular) is widely used in science. A density of more than 5Â g/cm3 is sometimes quoted as a commonly used criterion and is used in the body of this article.
Sterling silver Fine silver, for example 99.9% pure silver, is relatively soft, so silver is usually alloyed with copper to increase its hardness and strength. Sterling silver is prone to tarnishing[1][2], and metals other than copper can be used in alloys to reduce tarnishing, as well as casting porosity and firescale. Such metals include germanium, zinc, platinum, silicon, and boron. Recent examples of alloys using these metals include Argentium, Sterlium, Sterilite, and Silvadium.[3]