Element

Element, in chemistry, substance that cannot be broken down into simpler substances by normal chemical processes. Elements are generally mixtures of different isotopes. The elements are classified by physical properties as metals, metalloids, and nonmetals, and by chemical properties and atomic structure according to the periodic table. Most elements exhibit allotropy (more than one elemental form), and many are molecular. The elements have all been built up in stars from hydrogen by complex sequences of nuclear reactions.

Robert Boyle (1627–91) was the first to distinguish between elements and compounds. The first scientific list of elements was prepared by Antoine Lavoisier in 1789. He listed 33 substances, mistakenly including heat and light. By the mid-1800s it became apparent that certain elements had similar properties and could be grouped together. The first periodic tables were produced and stimulated the search for the undiscovered elements that would fill the gaps in the table. By 1925 all the naturally occurring elements had been discovered. Now, 109 elements are known, although elements 104 through 109, created within the past 30 years, have not been officially recognized by the International Union of Pure and Applied Chemistry. Sixteen of these have been produced artificially. In 1996, scientists stated that they had created a new element. However, element 112 disintegrated within one-thousandth of a second. Element 112 is seen as a steppingstone to the creation of element 114.

See also: Boyle, Robert; Chemistry.