![]() For instance, tellurium (Te) was clearly a chalcogen, in the oxygen family, and iodine (I) was clearly a halogen, based on their properties, but the weights were wrong. Notice how the the valences repeat every 7 elements when they are arranged according to atomic mass.īut there were some problems with the table. Here's a smaller version of the periodic table that leaves out the elements Mendeleev and Meyer found most problematic (transition metals, rare earths) and the group that hadn't been discovered yet (noble gases). Mendeleev used this to predict the properties of undiscovered elements. The modern version of this periodic arrangement is the Periodic Table.Īlso, within a group (sharing a valence) properties like density, boiling point, heat capacity, etc follow a simple progression. Using Cannizzaro's atomic weights, Mendeleev and Lothar Meyer made a great discovery, the periodic law: If you arrange the elements by their atomic weights, there is a periodic repetition in properties such as valence.
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