New Elements and Substances.

In chemistry in the 1930s most of the holes on Dmitry Ivanovich Mendeleyev's periodic table of chemical elements were filled. Emilio Segre, working from the foundation of demonstrations carried out by Robert Oppenheimer, tracked down the element with atomic number 43, technetium, which turned out to be the simplest element with no isotope. Only the elements for atomic numbers 61, 85, and 87 were missing, with 87 being discovered by French chemist Marguerite Perey in 1939 and named francium for her native country. Work on discovering stable isotopes to various elements also continued. In 1931 Harold Urey was able to isolate an isotope of hydrogen with one proton and one neutron, which was named deuterium. In 1935 physicist Arthur Jeffrey Dempster showed that uranium has one isotope occurring in one out of 140 atoms, uranium 235. This substance would become essential to the manufacture of the first atomic bomb.

Vitamins.

Several...