Mendeleev & The Periodic Table

Increasing Atomic Mass Similar Chemical Properties

Mendeleev’s Table Organized elements by increasing atomic mass so that elements with similar chemical properties were in the same column.

Mendeleev’s Prediction After Mendeleev placed all the known elements in his periodic table, several empty spaces were left. In 1871 Mendeleev predicted the existence and properties of elements that would fill three of the spaces. By 1886, all three of these elements had been discovered.

Mendeleev’s Prediction Predicted Eka-aluminum in 1871 –Soft metal –Low melting point –Density of 5.9 g/cm 3 Found: Gallium in 1875 –Soft metal –Melting Point 29.7 C –Density of 5.91 g/cm 3

Mendeleev’s Predictions

Usefulness of His Table The close match between Mendeleev’s prediction and the actual properties of new elements showed how useful his periodic table could be.

Henry Moseley (1913, British) –Organized elements by increasing atomic number. –Fixed the elements that Mendeleev had to switch based on atomic mass. –Now, no elements were out of order.

ChemCatalyst The atomic mass of silver is amu. The atomic mass of gold is amu. Where would you place these elements on the periodic table you created in Lesson 9: Create a Table? Explain your reasoning.

The card sort table can be opened up to accommodate more elements.

Evolution of the Periodic Table

Add Mendeleyev’s remaining elements.

Check-in Which of these elements would be grouped together on the periodic table? Explain your thinking. cadmium Cd moderately soft, silvery, solid, metal reacts very slowly with water found in CdCl 2 (s) zinc Zn moderately hard, silvery, solid, metal reacts very slowly with water found in ZnCl 2 (s) iodine I purple, solid, nonmetal reacts slowly with metals found in ICl(s) mercury Hg silvery, liquid, metal does not react with water found in HgCl 2 (s)