Question

Note on historical background in the study of classification of elements.
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Answer 1

Answer:

Historical background of classification of element: Earlier, an attempt was made to classify the elements into metals and non-metals. Metals: An element is a metal if it has the following properties. 1) It is lustrous i.e. it has shining of surface. 2) It is a good conductor of heat and electricity.

Explanation:

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Answer 2

Explanation:

In 1863, Dobernier classifies the elements into groups of three elements such that the three elements had similar properties and the atomic mass of the middle element was the arthematic mean of the atomic masses of the first and three elements. The group of such three elements was known as Triads.