Question

Who arranged the elements with similar properties into groups?

Answer 1

Hint : This is a question from the chapter periodic classification of elements. To answer this question you must have an idea of the periodic table, its properties, etc. Mainly you should be able to analyze the trends by yourself. If you cannot imagine or analyze by yourself, then it is a little bit difficult for you to tackle this problem. The detailed solution of this question is given below.

Complete Step By Step Answer:
Johann Dobereiner was the man who arranged the elements with similar properties into groups. He gave the five triads. He was a German chemist and classified different groups of three elements into groups known as triads. He gave these triads in $1829$ . He observed that groups of three elements known as triads can be formed having similar physical and chemical properties. According to his triad, the arithmetic mean of the atomic masses of the first and third element would be approx. equal to the atomic mass of the second or middle element. In his triad $1$ he took the alkali metals and these are lithium, sodium, and potassium. In his triad $2$ he took the elements calcium, barium, and strontium. In his triad $3$ he took the halogens which are chlorine, bromine, and iodine. If you took the arithmetic sum of the atomic masses of the first and third elements in each triad, you will get that it is equal to the atomic mass of the second element.

Note :
There are also the limitations of these Dobereiner’s triads like the new discovered elements made this model obsolete. They did not fit into the triads. Only $5$ Dobereiner triads were found. Not only newly discovered elements fit into these triads even the existing one did not fit into these triads.