In other words, elements could not actually exist in these spaces, spaces which only existed in the realm of human bookkeeping. Other gaps, however, were not due to undiscovered elements, but merely resulted from the properties of electron orbitals in atoms: upper rows of the table represent orbitals with fewer possible electrons and hence fewer elements, so displaying the lower rows properly below the upper ones leaves gaps in the upper rows. The later discovery of those elements (including germanium and gallium) helped validate Mendeleev's work. Mendeleev correctly predicted that some of these gaps represented elements that had not been discovered yet, and even predicted their properties based on the patterns in the table. Notably, this system left obvious gaps at the top of the table. The original version of this table was developed by Russian chemist Dmitri Mendeleev in 1869, when he realized that certain properties repeated periodically as elements became more massive. The periodic table of the elements is a display which arranges all of the 118 ( currently) known chemical elements by atomic number and sorts them into columns such that each column contains a group of elements displaying similar chemical properties. Title text: Most chemists thought the lanthanides and actinides could be inserted in the sixth and seventh rows, but no, they're just floating down at the bottom with lots more undiscovered elements all around them.
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