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Development of the periodic table The periodic table developed gradually by contributions from various scientists. This eventually led to the modern periodic table. 1. Dobereiner began with the development by grouping elements based on their similarities and classified them using their relative atomic mass. Dobereiner also identified a 'triad' in the list of elements. Calcium, strontium and barium had similar chemical properties. He noticed that the atomic weight of strontium fell midway between the weights of calcium and barium. (Ca 40.1 + Ba 137.5) × 0.5 = 88.7 Sr = 87.6 2. In order of increasing atomic weights, Newlands pointed out that every eighth element had similar properties, e.g. Hydrogen and Lithium (see fig.1). He called this the 'Law of Octaves'. 3. Mendeleev placed elements according to their increase in atomic mass. He left gaps for undiscovered elements. Mendeleev predicted the properties of the unknown elements based on their 'periodic properties', (see fig. 2). Two of these...

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