Periodic system - An overview of the world
Fire, water, earth, air: 400 years before Christ, the prevailing view was that the world consisted of just four elements. By the 19th century, a lot more was known. In fact, 63 elements had been discovered by then, for which chemist Julius Lothar Meyer devised a system. At the same time as Russian scientist Dmitri Mendeleev, he placed elements with similar chemical properties one above the other, and arranged substances with neighbouring atomic weights next to one another in a row. He was amazed to find that similar chemical properties are periodically repeated. The table, however, had some gaps, though these could be filled – mentally, at least – thanks to the new system: even though various elements had yet to be discovered, their atomic mass and chemical properties could be predicted in advance.
Significance: today, the periodic table contains 118 elements. The lightest of them is hydrogen. An element's position in the periodic table does not indicate the atomic weight, as Meyer originally believed, but the number of protons in its nucleus.
Invented by: Julius Lothar Meyer
In: 1864
Special Information: The periodic system has even been used as a source of musical inspiration: in 1959 American singer Tom Lehrer wrote a song called "The Elements" which cites the names of all 102 elements known to date.
