Mendeleev and his periodic table of elements

• 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.