- The majestic table of elements that hangs on the walls of chemistry classrooms across the world has turned 150 years old in 2019.
- The ‘Periodic Table of Elements’, or simply, ‘The Table’ for many, was written by Dmitri Ivanovich Mendeleev on 17th February 1869.
- Looking back, the Table opens a window to the world of inanimate matter.
- Mendeleev’s profound impact on chemistry is comparable to those of his contemporaries, Gregor Mendel and Charles Darwin in genetics and evolution, respectively.
- Therefore, the United Nations General Assembly and UNESCO have decided to celebrate 2019 as the “International Year of the Periodic Table of Chemical Elements (IYPT2019)”.
- Mendeleev was not the first one to create a table of elements.
Earliest of such efforts was due to the father of modern chemistry, Antoine Lavoisier in 1789 who classified them in terms of their properties.
John Newlands introduced the concept of octaves in chemistry, wherein properties repeat for every eighth element. There were other attempts too.
- Mendeleev’s finding was that “The elements, if arranged according to their atomic weights, exhibit an evident stepwise variation of properties”.
- “The elements, if arranged according to their atomic weights, exhibit an evident periodicity of properties”.
- While putting together all the 63 elements known at that time, his periodic table placed four slots between the known ones with question marks.
- He labeled them with a prefix, eka. All eka elements were discovered subsequently: eka-aluminum (gallium) in 1875; eka-boron (scandium) in 1879; eka-silicon (germanium) in 1886 and eka-manganese (technitium) in 1937.
- Periodic table predicted the properties such as metallicity, density, melting point, etc., of the eka elements.
- Today, all the 118 elements are put in the periodic table based on the periodic law.