![]() 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, smelting, industrial waste, agricultural runoff, occupational exposure, paints and treated timber. Other heavy metals, such as arsenic, 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, none of which 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. Not to miss out, element 102, Nobelium, No, is named in honor of Alfred Nobel, who set aside his vast fortune to establish Nobel Prizes.Heavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers. Mendeleev never received a Nobel Prize for his work, but element 101 was named Mendelevium, Md, after him. For instance they discovered phosphorus when they isolated it from urine. Over time these gaps have gradually been filled in as scientists unearthed new elements. Not only did Mendeleev arrange the elements in the correct way, but he also had the foresight to leave gaps for undiscovered elements. At that time, he had only 50 elements to arrange. He wrote the properties of the elements on pieces of card and rearranged them until he realised that, by putting them in order of increasing atomic weight, certain properties of elements regularly occurred. Then in 1869, a Russian scientist called Dmitri Mendeleev produced one of the first practical periodic tables. Several other attempts were made to group elements together over the coming decades. The earliest attempt to classify the elements was in 1789, when Antoine Lavoisier grouped the elements based on their properties into gases, non-metals, metals and earths. The discovery of other elements followed regularly and soon it became necessary to arrange them in some sort of order. However, the first scientific discovery of an element occurred in 1649 when Hennig Brand discovered phosphorous. Copper has been used by humans for as much as 7000 years and elements such as gold, silver, tin, lead and mercury have been known for many thousands of years. ![]()
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