Mendeleev believed that scientists would finally discover the missing elements and confirm his theory. He predicted the properties of the three missing elements by looking at the properties of the neighboring elements. Between 1875 and 1886, three missing elements, gallium, scandium, and germanium, were discovered. Each had the properties that were predicted. As more elements were discovered, scientists recognized the advantages of using the Periodic Table of Elements.

During the last several centuries, 109 elements have been discovered. Ninety-two elements occur naturally in nature and seventeen are manmade elements called Transuranic elements. In 1995, scientists created the first anti-hydrogen atom at the CERN research facility in Europe. Anti-hydrogen is a mirror image of matter and contains a one position (negative electron) that orbits an anti-proton nucleus. Normal hydrogen atoms consist of electron that obits the one proton nucleus.

In 2001, Norm Hansen identified 108 additional antimatter elements, which he were incorporated into a Periodic Table of Matter-Antimatter Elements. There is symmetry between the matter and antimatter elements. He identified each of the antimatter element's nuclear, physical, and chemical properties to such an extent that people know almost as much about antimatter as matter. He added a superscript ^A before the element or symbol to indicate element was an antimatter element. For example, hydrogen and oxygen are ^Ahydrogen and ^Aoxygen respectively.