Timeline: The Discovery of Elements

Assigning credit for the discovery of a new element is often a difficult and complicated process. First, many elements were in use well before recorded history. In some cases, these elements were known in the form of their compounds, but not as pure elements. Elements that fall into this category include carbon, copper, gold, iron, lead, mercury, silver, sulfur, tin, and, perhaps, zinc. In addition, the discovery of an element has seldom been a single, clear-cut event that occurs in such a way that everyone agrees that “X” should receive credit for discovering the element. Instead, the first step in the process of discovery is often the recognition that a new substance has been found—a new mineral, rock, compound, or other material— that has properties different from anything previously known. This discovery may lead a chemist (or a number of chemists) to suspect the existence of a new element. The next step may be to isolate the element, either in its pure form or, more commonly, as a compound, such as the oxide or sulfide of the new element. Finally, someone is able to prepare a pure sample of the element, which the world then sees for the first time. An example of this sequence of events can be seen in the elements that make up groups 1 and 2 of the periodic table. Most of those elements were known in one form or another for centuries. But it was not until the early 1800s that Sir Humphry Davy found a method for isolating the pure elements from their oxides. The process becomes even more complicated when a truly new element is discovered which, sometime later, is found not to be a single element, but a mixture of two or more new elements. The story of the discovery of the rare earth elements is probably the best example of this process.