Johann Wolfgang Döbereiner (jan 1, 1829 – jan 1, 1829)

Description:

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Introduction and Basis:
Johann Wolfgang Döbereiner was a German scientist and chemist who in 1829 found some groups of three elements which showed similar properties. He placed those various groups of threes into groups called triads, also known as Döbereiner's triads. The triads were grouped based on both physical and chemical properties. He found that the atomic masses of these elements, as well as other triads, formed a pattern.

Examples:
An example of one of the triads is Lithium (Li), Sodium (Na), and Potassium (K).
When the atomic masses of lithium and potassium were averaged together (6.94 + 39.10)/2 = 32, it was approximately equal to the atomic mass of sodium (22.99).
When we calculate the mean of the atomic masses of lithium and potassium (7 +39)/2 = 23, we can see that it is approximately the same as the atomic mass of sodium.
These three elements also displayed similar chemical reactions, such as vigorously reacting with the members of another triad: Chlorine (Cl), Bromine (Br), and Iodine (I).

Limitations:
His theory of triads came with shortcomings and limitations as not all of the known elements at that time could be classified in that way. He could only identify SOME triads from the elements known at that time. Other triads did not obey the rule. Hence, the system of triads was not useful.
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