# History of the 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 a Periodic Table?

Periodic table is just a table in which elements are randomly arranged or the elements are arranged in the fixed pattern.

The periodic table is basically a table in which elements are arranged on the basis of the atomic number. Elements having similar chemical properties fall under the same vertical column. These vertical columns are known as the periodic table groups.

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#### Higher Elements Periodic Table

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) that 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 in 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 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 Octaves

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 of up to calcium.

 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 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.

Mendeleev’s Periodic Table

### Limitations of Mendeleev’s Periodic Table

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

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

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