expectation that elements with those atomic masses would be discovered. Those blanks correspond to the elements we now know as scandium, gallium, germanium, and technetium. Figure: Mendeleev’s Periodic Table, as Published in the German Journal Annalen der Chemie und Pharmacie in 1872: The column headings and are German for and “Reihen” “Gruppe” “row” “group.” Formulas indicate the type of compounds formed by each group, with standing for element” “R” “any and superscripts used where we now use subscripts. Atomic masses are shown after equal signs and increase across each row from left to right. The most convincing evidence in support of Mendeleev’s arrangement of the elements was the discovery of two previously unknown elements whose properties closely corresponded with his predictions (Table below). Two of the blanks Mendeleev had left in his original table were below aluminum and silicon, awaiting the discovery of two as-yet-unknown elements, eka-aluminum and eka-silicon (from the Sanskrit eka, meaning as in beyond aluminum”). The observed “one,” “one properties of gallium and germanium matched those of and so well that eka-aluminum eka-silicon once they were discovered, Mendeleev’s periodic table rapidly gained acceptance. Gallium eka-Silicon Germanium Property Aluminum (observed) (predicted) (observed) (predicted) atomic 68 69.723 72 72.64 mass dirty-gray gray-white metal metal metal metal element low mp* mp = 29.8°C high mp mp = 938°C d = 5.9 d = 5.91 d = 5.5 d = 5.323 g/cm3 g/cm3 g/cm3 g/cm3 oxide E2O3 Ga2O3 EO2 GeO2
expectation that elements with those atomic masses would be discovered. Those blanks correspond to the elements we now know as scandium, gallium, germanium, and technetium. Figure: Mendeleev’s Periodic Table, as Published in the German Journal Annalen der Chemie und Pharmacie in 1872: The column headings “Reihen” and “Gruppe” are German for “row” and “group.” Formulas indicate the type of compounds formed by each group, with “R” standing for “any element” and superscripts used where we now use subscripts. Atomic masses are shown after equal signs and increase across each row from left to right. The most convincing evidence in support of Mendeleev’s arrangement of the elements was the discovery of two previously unknown elements whose properties closely corresponded with his predictions (Table below). Two of the blanks Mendeleev had left in his original table were below aluminum and silicon, awaiting the discovery of two as-yet-unknown elements, eka-aluminum and eka-silicon (from the Sanskrit eka, meaning “one,” as in “one beyond aluminum”). The observed properties of gallium and germanium matched those of eka-aluminum and eka-silicon so well that once they were discovered, Mendeleev’s periodic table rapidly gained acceptance. Property (predicted) Gallium (observed) eka-Silicon (predicted) Germanium (observed) atomic mass 68 69.723 72 72.64 element metal metal dirty-gray metal gray-white metal low mp* mp = 29.8°C high mp mp = 938°C d = 5.9 g/cm3 d = 5.91 g/cm3 d = 5.5 g/cm3 d = 5.323 g/cm3 oxide E2O3 Ga2O3 EO2 GeO2 Aluminum
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