Periodic Classification of Elements

The first classification of elements

The first classification of elements was into metals and non-metals. This was useful only in a limited way because some elements, such as germanium an

William Prout's work in 1815 showed

William Prout's work in 1815 showed that the atomic mass of an element remains constant, so atomic mass became a possible basis for classification.

In 1829

In 1829, J.W. Dobereiner grouped elements into sets of three called triads. In each triad, the middle element had an atomic mass nearly equal to the a

In 1864

In 1864, John Alexander Newlands arranged elements in increasing order of atomic mass and observed that every eighth element had properties similar to

In 1869

In 1869, D'mitri Mendeleev arranged 63 known elements and their compounds mainly by increasing atomic mass and stated that the chemical and physical p