The Periodic Table
The History of the Periodic Table 1789: Lavoisier published a list of 33 chemical elements, grouping them into gases, metals, nonmetals, and earths 1829: Johann Wolfgang Döbereiner observed that many of the elements could be grouped into triads based on their chemical properties. Lithium, sodium, and potassium, for example, were grouped together in a triad as soft, reactive metals.
Classification of Elements 1858: August Kekulé observed that carbon often has four other atoms bonded to it. Methane, for example, has one carbon atom and four hydrogen atoms. This concept eventually became known as valency; different elements bond with different numbers of atoms. 1864: Julius Lothar Meyer published a table of the 49 known elements arranged by valency. The table revealed that elements with similar properties often shared the same valency. [ [
1865: John Newlands listed elements in order of increasing atomic weight, and noted that similar physical and chemical properties recurred at intervals of eight. His Law of Octaves was ridiculed by Newlands' contemporaries, and the Chemical Society refused to publish his work. Newlands able to draft a table of the elements and used it to predict the existence of missing elements, such as germanium.
The First Periodic Tables 1869: Dmitri Mendeleev and Lothar Meyer independently published their periodic tables. They both constructed their tables by listing the elements in rows or columns in order of atomic weight. Both started a new row or column when the characteristics of the elements began to repeat.
Meyer Table (1870) IIIIIIIVVVIVIIVIIIIX BAlIn(?)Tl CSi TiZr SnPb NP V As Nb Sb Ta Bi OS Cr Se Mo Те W FCl Mn Fe Co Ni Br Ru Rh Pd I Os Ir Pt LiNaK Cu Rb Ag Cs Au BeMgCa Zn Sr Cd Ba Hg
Elements Arranged by Valency
Why Does Mendeleev Get The Credit? The success of Mendeleev's table came from two decisions: He left gaps in the table when it seemed that the corresponding element had not yet been discovered. The second decision was to occasionally ignore the order suggested by the atomic weights and switch adjacent elements, such as cobalt and nickel. With the development of theories of atomic structure, it became apparent that Mendeleev had unintentionally listed the elements in order of increasing atomic number or nuclear charge.
The Modern Periodic Table 1923: Horace Groves Deming published the 18-column periodic table. 1928: Deming’s table was widely circulated in American schools
The Structure of the Periodic Table The rows (periods) correspond to the princpal energy levels of the outer electrons The columns contain elements with the same number of outermost electrons in the same sublevel
All Periodic Tables Have The Following: The symbol of each element The atomic number of each element The atomic mass of each element
Other Periodic Table Variations
Janet Periodic Table
Circular Periodic Tables