Till the 18th century scientists were able to isolate many elements present in our earth’s crust. In the beginning, they classified these elements broadly into two categories namely metals and nonmetals. But as the number of elements increased over the period of years, this classification was not sufficient to group them efficiently. Hence, they started looking for alternate ways in order to group all the elements in the most efficient manner. Scientists carried out various tests with a different set of elements to club the elements based upon the observation they noticed. Some of the popular methods including Dobereiner’s triads and Newland’s law of octaves are explained below:
Dobereiner’s triads: Johann Wolfgang Döbereiner was a German chemist who tried to arrange the elements with similar properties into groups. In the year 1817, after conducting many experiments and obtaining their observations he finally categorized elements in a group of three. He called these groups as ‘triads’ since each group contained three elements. The basis of categorization of these elements was the atomic mass of the elements involved in each triad. Elements in each triad were arranged in such a way that the atomic mass of the middle element is equal to the average of the first and last element. For example Lithium (Li), Sodium (Na) and Potassium (K).
Newland’s law of octaves: In the year 1866, an English scientist, John Newlands arranged the elements in the order of increasing atomic masses. Till then only 56 elements were known to us. He started with hydrogen which has the lowest atomic mass and finally ended at thorium which was the element known to have highest atomic mass at that time. He noticed that every eighth element exhibits similar properties as compared to the first element. He called this law as the ‘Law of Octaves’ better known as ‘Newland’s Law of Octaves’. According to Newland’s Law of Octaves, as the observed properties of lithium and sodium are same, sodium is placed at the eighth position with respect to lithium. A general representation of various elements according to Newland’s Law of octaves is given below:
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