Era of discovery
Classification of the periodic table according to epochs of the discovery of the elements. The oldest elements have been known since antiquity, others were only synthesized in the 2000s. Most elements were discovered in the 19th century.
The discovery of phosphorus by Hennig Brand (1669) marked the beginning of the age of discovery of most elements, including uranium from pitchblende by Martin Heinrich Klaproth in 1789.
Over 20 elements, including many heavy ones and also those of the rare earths, could be discovered by the end of the 19th century, so that almost all naturally occurring elements were known around 1900.
In the first half of the 19th century, more than 25 new elements were discovered, which also serve as an indicator for the new technical-scientific state of development.
Of the elements by scientific definition, only a few were known in pure form in antiquity, which either occur naturally (i.e. native) or could be melted from ore.
Through new technological possibilities, the emerging quantum age and gained knowledge about radioactivity and its applications, many radioactive elements were found by 1950.
After 1950, many new, non-naturally occurring elements (the transuranics) were synthesized partly in nuclear reactors, partly in particle accelerators. Such elements are characterized by instability and radioactive decay.
With the help of new methods of synthesis and sometimes considerable effort, further transuranics have been produced since 2000. Properties are often barely or still unexplored.