• 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.