Construction of the Periodic Table

Before the construction of the periodic table could ever come to fruition, the individual elements of which it is made had to be discovered. To be sure, elements such as copper, gold, mercury and silver have been commonly known since ancient times. However, according to Western Oregon University (WOU), German chemist Hennig Brand was the first to scientifically target an element. He discovered phosphorus. Two hundred years and 62 other elemental unearthings later, Russian chemist Dimitri Mendeleev revolutionized atomic thought by plugging this growing list of chemical constituents into the periodic table of the elements.

Significance

• Dimitri Mendeleev's table appeared in the year 1869. A student of Robert Wilhelm Bunsen, the renowned St. Petersburg University lecturer arranged the elements in his table according to similarities in their properties and in ascending order by atomic weight. The beauty of Mendeleev's scheme was that he left holes in the table, anticipating elements that would be found in years to come.

Features

• As soon as the 1880s, the gaps in Mendeleev's table were beginning to get filled in, serving to substantiate his approach and gaining him fame not just in Russia but worldwide. It must be said, however, that it seems French geologist A.E. Beguyer de Chancourtois technically beat Mendeleev to the punch. In 1862, he published a table showing weights and periodicity--of chemical and physical properties--in the way that Mendeleev did. However, he muddied his chart with compounds and ions.

  Then there was Lothar Meyer. Unlike de Chancourtois, Meyer achieved amazingly similar results to Mendeleev. An abbreviated version of a periodic chart--with half of the known elements along with atomic weights and valence charges--appeared in Meyer's 1864 textbook. Meyer constructed a longer table in 1868. Mendeleev simply beat Meyer's publication date of 1870, according to WOU.

Noble Gases

• Lord Rayleigh (born John William Strutt) discovered argon, a new gaseous element, in 1895. It was a group unto itself and was to become one of the six noble gases. The other gases are helium, krypton, neon, radon and xenon. These colorless and odorless elemental gases were deemed inert (slow to react) because their oxidation number of 0 prevented them from easily forming compounds. However, scientists in the early 1960s began successfully creating gaseous compounds with them. The discovery of and experimentation with noble gases significantly contributed to an understanding of atomic structure.

Atomic Structure

• Why did the properties of the elements recur periodically? Mendeleev's chart demonstrated the periodic nature of the elements, but it was up to the science minds of the 20th century to explain the reasons for this intermittency.

  With the discovery of isotopes--atoms of the same element with different numbers of neutrons--it became apparent that atomic weight was not necessarily key in periodic law, as Mendeleev and Meyers had suggested. Instead, the properties of the elements varied periodically with atomic number.

Twentieth Century

• With Niels Bohr's investigations into the organization of electrons into shells in 1913, the question of why periodic law exists was answered as the electronic structure of the elements came into focus.

  Glenn Seaborg's studies in the middle of the 1900s represented the last major alterations to the periodic table. He founded all the transuranic elements--those elements heavier than uranium--from 94 to 102, beginning with his discovery of plutonium in 1940. Seaborg reordered the periodic table by placing the actinide series below the lanthanide series. Seaborg won the Nobel Prize in chemistry in 1951. Element 106 is named seaborgium (Sg) in recognition of his achievements.