In 1869, when Dmitri Mendeleev published his periodic table, the space under iodine was empty; after Niels Bohr established the physical basis of the classification of chemical elements, it was suggested that the fifth halogen belonged there.
The space under iodine was empty. This was in 1869. Dmitri Mendeleev published his periodic table. The fifth halogen belonged there. It was suggested this. This was in 1869. Bohr established the physical basis of the classification of chemical elements. This was after Niels. This was what Dmitri Mendeleev published his periodic table.