Attempts Made By Johann Döbereiner and Johann Newlands to Classify the Elements

Johann Wolfgang Döbereiner began to formulate one of the earliest attempts to classify the elements. In 1817 Johann Döbereiner noticed that the atomic weight of strontium fell midway between the weights of calcium and barium, elements possessing similar chemical properties.

Ca   Sr   Ba     (40 + 137) ÷ 2 = 88 

40     88     137

In 1829, after discovering the halogen triad composed of chlorine, bromine, and iodine and the alkali metal triad of lithium, sodium and potassium he proposed that nature contained triads of elements the middle element had properties that were an average of the other two members when ordered by the atomic weight (the Law of Triads).

Li   Na  K         Cl   Br   I 

7     23     39           35    80   127

English chemist John Newlands (1837-1898), having arranged the 62 known elements in order of increasing atomic weights, noted that after interval of eight elements similar physical/chemical properties reappeared.  Newlands noted that many pairs of similar elements existed which differed by some multiple of eight in atomic number. However, his law of octaves, likening this periodicity of eights to the musical scale, was ridiculed by his contemporaries. It was not until the following century, with Gilbert N. Lewis' valence bond theory (1916) and Irving Langmuir's octet theory of chemical bonding (1919) that the importance of the periodicity of eight would be accepted. Newlands was the first to formulate the concept of periodicity in the properties of the chemical elements. In 1863 he wrote a paper proposing the Law of Octaves: Elements exhibit similar behaviour to the eighth element following it in the table.