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Mendeleev and his periodic table of elements


From UPSC perspective, the following things are important :

Prelims level : Modern Periodic Table

Mains level : Not Much

  • This newscard is supplementary to an must-read article published in the The Hindu

The Modern Periodic Table

  • The periodic table is an arrangement of all the elements known to man in accordance with their increasing atomic number and recurring chemical properties.
  • They are assorted in a tabular arrangement wherein a row is a period and a column is a group.
  • Until 1863, the world was aware of only 56 known elements.
  • The rate of scientific progress was such that every year, a new element was being discovered.
  • It was during this time that Mendeleev came up with the idea of the Periodic Table.
  • He published the Periodic Table in his book– The Relation between the Properties and Atomic Weights of the Elements.
  • Mendeleev said that he arrived at the idea in his dream, where he saw all chemical elements falling into place on a table according to their chemical properties.
  • Mendeleev had found a definitive pattern following which, each element could be placed according to their atomic weight.
  • He had also predicted the qualities of the ‘missing’ (yet to be discovered) elements and gave them Sanskrit names.

Its Evolution

  • The noble gases including helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn) were added to the table between 1895 and 1901.
  • Likewise, additions have been made to the periodic table as new elements have been discovered in the last hundred years
  • In 1914, English physicist Henry Gwyn-Jeffries Moseley found out that each atomic nucleus can be assigned a number, according to the number of protons in that atom.
  • This changed the way the periodic table worked. The table was redesigned according to the atomic number of elements rather than their atomic weight
  • Rare-earth elements, including the elements in the Lanthanide series, were included in the atomic table in the late 19th century.
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