Correct predictions

The greatness of Mendeleev was that not only did he leave spaces for elements that were not yet discovered but he predicted properties of five of these elements and their compounds. How foolish he would have seemed if these predictions had been incorrect but fortunately for him three of these missing elements were discovered by others within 15 years (ie within his lifetime). The first of these Mendeleev had called eka-aluminium because it was the one after aluminium (eka = 1 in Sanskrit) and was identified in Paris (1875) by Paul Emile Lecoq de Boisbaudran who named it gallium after the Latin name for France. Mendeleev was ecstatic when he heard of its properties which nearly matched his eka-aluminium. However de Boisbaudran's value for gallium's density (4.9 g/cm³) differed from Mendeleev's prediction. Mendeleev told the Frenchman, who re-measured the density to find Mendeleev was right! It is interesting to speculate whether de Boisbaudran was pleased or irritated by this. The table compares Mendeleev's predictions with de Boisbaudran's discovery.

Within the next ten years Swede Lars Nilson (1879) identified scandium, predicted by Mendeleev as eka-boron and German Clemens Winkler (1886) discovered germanium which he realised was Mendeleev's eka-silicon. These discoveries established the acceptance of the Russian's table, although two other elements whose properties were predicted were not discovered for 50 years.

One thing that Mendeleev did not predict was the discovery of a whole new Group of elements, the noble gases, by the Scot William Ramsay and co-workers during the last decade of the 19^th century (see The discovery of new elements). Mendeleev was at first dismayed by this but before he died in 1907 realised that Ramsay's discoveries were further proof of the Periodic Table, not a contradiction. Ramsay was awarded a Nobel Prize for discovering five elements. Mendeleev never received that honour However, an element, atomic number 101, has been named after Mendeleev, an even rarer distinction. This is surely deserved by the original formulator of the Periodic Table.

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Discovery of the Periodic Table

Just as we have tables in mathematics to remember the calculation of various numbers, a periodic table is also a must when it comes to calculation of different properties and the atomic numbers of various chemical elements. Let us find out what a periodic table is and how it was discovered.

Since ages, people have known elements like gold, silver and carbon. These elements couldn't be changed using any chemical method as each element has a unique number of protons and atoms. These elements can also be differentiated as they have different properties. However soon there were many elements that were discovered and hence the need for a periodic table was felt. Let us find out what a periodic table is and how it was discovered.