Do you know how the periodic table was formed? Mendeleev was the first chemist who gave us a proper tabular periodic table. But how did he come up with it? On what basis did he arrange the elements? Who were the other chemists who tried doing so before and after him? Let’s explore everything about the historical development of the Periodic table.
The Periodic Table
What is the periodic table? Is it just a table containing all elements? Do the elements follow a certain pattern? The periodic table is basically a table in which elements are arranged on the basis of atomic number. A vertical column has various elements having similar chemical properties. Periodic table groups are these vertical columns.
History of the Periodic Table
Let us start with the very first theory of periodic table.
1) Doberiener’s Triads
The German chemist, Johann Dobereiner in 1800 first observed similarities in the elements on the basis of their properties. He saw that there are groups consisting of three elements (triads) which have similar chemical and physical properties. In every group, the atomic weight of the middle element was half of the sum of the atomic weight of the other two elements.
Properties of the middle element were also at the halfway of both the elements. Dobereiner called this grouping method as the law of triads. Later on, it was found that this law was not true for every element and hence it was not successful.
|Element||Atomic Weight||Element||Atomic Weight||Element||Atomic Weight|
For example: Atomic weight of Na = Atomic weight of Li + Atomic weight of K = (7+39)/2 = 23
2) Newland’s Octave
In 1865, after the failure of Doberiener’s triad the English chemist, John Alexander Newlands gave the law of octaves. According to him, elements can be arranged in ascending order of their atomic weights. He also said that in this arrangement every eighth element of a row had similar properties to that of the first element of the same row, depicting the octaves of music. This law was also dismissed as it was only true for elements up to calcium.
3) Mendeleev Periodic Table
The real development in the periodic table took place after the development of Mendeleev periodic table. He gave a law which states that “The properties of an element are the periodic function of their atomic masses”. He arranged elements in periods (horizontal rows) and groups(vertical columns) in the increasing order of atomic weights. The vertical column consists of elements that have similar properties.
Learn more about the concept of Electronegativity here.
A Solved Example for You
Q: What were the limitations of Mendeleev periodic table?
Solution: The periodic table given by Mendeleev has some limitations. They are:
- It did not provide a clear idea about the structure of an atom.
- In order to arrange elements in a group, we had to reverse the order of atomic weight several times.