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Achievment of mendeleev\' s periodic table |
| Answer» Achievements of Mendeléev’s periodic table\telement with a slightly greater atomic mass were placed\tbefore an element with a slightly lower atomic mass with an inverted sequence so as to group the elements with similar properties. For example, cobalt with atomic mass 58.9 was placed before nickel with atomic mass 58.7.\tHe left some gaps in the Periodic Table with the prediction of\texistence of some elements that were not discovered at that time.\tHe named the future elements by prefixing a Sanskrit numeral, Eka (one) to the name of preceding element in the same group.\tFor instance, scandium, gallium and germanium, discovered later, have properties\tsimilar to Eka–boron, Eka–aluminium and Eka–silicon, respectively.\tNoble gases like helium (He), neon (Ne) and argon (Ar) were discovered\tlater as they are present in exceptionally low concentrations in the atmosphere due to their inertness. | |