Mendeleev's predicted elements

In 1869, Professor Dmitri Mendeleev created the first periodic table of chemical elements. He arranged the elements from the lightest one to the heaviest one. When he proposed his periodic table, he placed empty spaces between some elements. He said that the empty spaces were for undiscovered elements. Mendeleev had also predicted the properties of these undiscovered elements.

Naming the undiscovered elements

Mendeleev gave temporary names for the undiscovered elements. He used the prefixes eka-, dvi- and tri- and combined it with any known elements in the same group with the undiscovered element. Eka-, dvi- and tri- are numbers 1, 2 and 3 in the Sanskrit language. The use of the prefix depends on how far the known element is from the unknown element. For example, germanium was called eka-silicon because silicon is placed one row above germanium, and rhenium was called dvi-manganese because manganese is placed two rows above rhenium. The names of these elements were changed after they were discovered.

Other scientists use the eka- prefix, too. Eka- is also used in the names of elements that Mendeleev did not predict. Before francium was discovered, it was called eka-caesium, and before astatine was discovered, it was called eka-iodine. The eka- prefix is also used to name transuranic elements (elements after uranium). For example, Oganesson is also called eka-radon, and untriennium (element number 139) is also called eka-actinium. Today, the IUPAC uses the systematic element name to give new elements a temporary name. This new way of naming elements depends on the atomic number of the element. It does not depend on the position of the element in the periodic table.