History Of The Development Of Modern Periodic Table

We should get familiar with the word periodic table before we start up with the history of the modern periodic table. Now what is periodic table? Is this just a table in which elements are randomly arranged or the elements are arranged in fixed pattern? Periodic table is basically a table in which elements are arranged on the basis of atomic number. Elements having similar chemical properties fall under the same vertical column.These vertical columns are known as the periodic table groups.

Doberiener’s triad:

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 atomic weight of the middle element was half of the sum of atomic weight of the other two elements. Properties of the middle element was also in the half way 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.

Doberiener’s triads

Element Atomic Weight Element Atomic Weight Element Atomic Weight
Li 7 Ca 40 Cl 35.5
Na 23 Sr 88 Br 80
K 39 Ba 137 I 127

 

For example: Atomic weight of Na =  \( \frac {Atomic ~ weight ~pf` Li~ +~Atomic~weight~of~k}{2}\) = \( \frac{7+39}{2} \) = 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 first element of the same row, depicting the octaves of music.This law was also dismissed as it was only true for elements upto calcium.

 

Newlands’ Octave

Element Li Be B C N O F
Atomic weight 7 9 11 12 14 16 19
Element Na Mg Al Si P S Cl
Atomic weight 23 24 27 29 31 32 35.5
Element K Ca
Atomic weight 39 40

 

Mendeleev’s periodic table:The real development in the periodic table took place after the development of Mendeleev’s periodic table.He gave a law which states that “The properties of 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.

Modern Periodic Table

Mendeleev’s periodic table

Limitations of Mendeleev’s periodic table:

  1. It did not provide a clear idea about the structure of atom.
  2. In order to arrange elements in a group, the order of atomic weight were reversed several times.

The discovery of new elements and their subsequent addition to periodic table keeps revealing new dimensions in periodicity. To explore more about periodic table please visit Byju’s YouTube channel.

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