We all know that there are 118 elements present in our periodic table. Out of these 118 elements, 94 elements are natural elements and 24 elements are synthetic elements. Back in the year 1800, only 30 elements were known. With the discovery of more and more elements, remembering the elements and their properties were burdensome for scientists. They started gathering information about the elements and categorizing it. The categorization of elements in a tabular form according to their properties became popular. The tabular form structure in which various elements are arranged according to their properties is known as the periodic table.
Dmitri Ivanovich Mendeléev, a Russian chemist, was the most important contributor to the early development of the periodic table. Many periodic tables were made but the most important one was Mendeleev periodic table.
In 1869, after the rejection of Newlands Octave Law, Mendeleev Periodic table came into the picture. In Mendeleev’s periodic table, elements were arranged on the basis of the fundamental property, atomic mass, and chemical properties. During Mendeleev’s work, only 63 elements were known. After studying the properties of every element, Mendeleev found that the properties of elements were related to atomic mass in a periodic way. He arranged the elements such that elements with similar properties fell into same vertical columns of the periodic table.
Among chemical properties, Mendeleev treated formulae of hydrides and oxides as one of the basic criteria for categorization. He took 63 cards and on each card, he wrote the properties of one element. He grouped the elements with similar properties and pinned it on the wall. He observed that elements were arranged in the increasing order of atomic mass and there was the periodic occurrence of elements with similar properties.
According to this observation, he formulated a periodic law which states:
“the properties of elements are the periodic function of their atomic masses.”
In Mendeleev periodic table, vertical columns in the periodic table and horizontal row in the periodic table were named as groups and period respectively.
- Some gaps were left for the elements yet to be discovered. Thus, if a certain new element is discovered, it can be placed in a new group without disturbing any existing group.
- He was unable to locate hydrogen in the periodic table.
- Increase in atomic mass was not regular while moving from one element to another. Hence, the number of elements yet to be discovered was not predictable.
- Later on, isotopes of elements were found which violated Mendeleev’s periodic law.
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