The Beginnings of the Periodic Table
Before written history, people were aware of some of the elements in the periodic table. Elements such as gold (Au), silver (Ag), copper (Cu), lead (Pb), tin (Sn), and mercury (Hg).
It wasn't until 1649, however, until the first element was discovered through scientific inquiry by Hennig Brand . That element was phosphorous (P).
By 1869, 63 elements had been discovered.
Creating Some Early Blocks for the Periodic Table
Between 1817-1829, Johann Dobereiner began to group elements with similar properties in to groups of three or triads. This began in 1817 when he noticed that the atomic weights of strontium, Sr, was halfway between the weights of calcium and barium. These elements possessed similar chemical properties. By 1829, he had discovered the a halogen triad made up of chlorine, bromine, and iodine and a alkali metal triad of lithium, sodium and potassium. He postulated that nature contained triads of elements in which the middle element had properties that were an average of the other two elements. Later, other scientists found other triads and recognized that elements could be grouped into set large than three. The poor accuracy of measurements such as that of atomic weights hindered grouping more elements.
Precursors to the Periodic Table
In 1862, A.E.Beguyer de Chancourtois was the first person to make use of atomic weights to reveal that the elements were arranged according to their atomic weights with similar elements occurring at regular intervals. He drew the elements as a continuous spiral around a cylinder divided into 16 parts. A list of elements was wrapped around a cylinder so that several sets of similar elements lined up, creating the first geometric representation of the periodic law
The musical analogy was ridiculed at the time, but was found to be insightful after the work of Mendeleev and Meyer were published.
The Fathers of the Periodic Table
Lothar Meyer and Dmitri Ivanovich Mendeleev independently produced remarkably similar versions of the periodic table of elements at the essentially the same time.
Meyer's 1864 textbook included a abbreviated version of a periodic table used to classify about half of the known elements. In 1868, Meyer constructed an extended table which he gave to a colleague for evaluation. This table unfortunately was not published until 1870, a year after Mendeleev's table was published.
Mendeleev predicted the existence and properties of unknown elements which he called eka-aluminum, eka-boron, and eka-silicon. The elements gallium, scandium and germanium were found later to fit his predictions quite well.
The Modern Periodic Table
Glenn Seaborg discovered the transuranium elements, atomic numbers 94 to 102. The completion of the actinide series allow Seaborg to redesign the periodic table into it current form. Both the lanthanide and actinide series of elements were placed under the rest of the periodic table. These elements technically should be placed between the alkaline earth metals and the transition metals, however, since this would make the periodic table too wide, they were placed below the rest of the elements.
Dr. Seaborg and his colleagues are also responsible for the identification of more than 100 isotopes of elements.
