Question

2. The basis of the classification
proposed by Dobereiner,Newlands and
Mendeleev was​

Answer 1

Answer:

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Answer 2

Answer:

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

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 =  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.

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      

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.

Explanation:

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