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Development of the Periodic Table
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Dobereiners Law of Traids
Johann Dobereiner, a German Chemist (1780-1849) grouped elements based on similarities. In 1829 Dobereiner proposed the Law of Triads which was the middle element in the triad had atomic weight that was the average of the other two members. -
First Periodic Table
Alexandre Beguyer de Chancourtois (1820-1886), professor of geology at the School of Mines in Paris, published in 1862 a list of all the known elements. -
Law of Octaves
English chemist John Newlands (1837-1898), having arranged the 62 known elements in order of increasing atomic weights, noted that after interval of eight elements similar physical/chemical properties reappeared. Newlands was the first to formulate the concept of periodicity in the properties of the chemical elements. In 1863 he wrote a paper proposing the Law of Octaves: Elements exhibit similar behavior to the eighth element following it in the table. -
Mendeleev's Periodic Table
Then in 1869, Russian chemist Dimitri Mendeleev (1834-1907) proposed arranging elements by atomic weights and properties (Lothar Meyer independently reached similar conclusion but published results after Mendeleev). Mendeleev's periodic table of 1869 contained 17 columns with two partial periods of seven elements each (Li-F & Na-Cl) followed by two nearly complete periods (K-Br & Rb-I). -
Mendeleev's Periodic Table
In 1871 Mendeleev revised the 17-group table with eight columns (the eighth group consisted of transition elements). This table exhibited similarities not only in small units such as the triads, but showed similarities in an entire network of vertical, horizontal, and diagonal relationships. The table contained gaps but Mendeleev predicted the discovery of new elements. -
Rayleigh and Ramsey
Lord Rayleigh (1842-1919) and William Ramsey (1852-1916) greatly enhanced the periodic table by discovering the "inert gases." In 1895 Rayleigh reported the discovery of a new gaseous element named argon. This element was chemically inert and did not fit any of the known periodic groups. -
Ramsey and Rayleigh
Ramsey followed by discovering the remainder of the inert gases and positioning them in the periodic table. So by 1900, the periodic table was taking shape with elements were arranged by atomic weight. -
Raylaigh and Ramsey Nobel Prizes
Rayleigh (physics) and Ramsey (chemistry) were awarded Nobel prizes in 1904. -
Mendeleev's Periodic Table
In 1906, Mendeleev came within one vote of receiving the Nobel Prize in chemistry. -
Rutherfords Experiment
Ernest Rutherford's landmark experiment of discovering the proton in 1911. -
Henry Moseley
Henry Moseley (1887-1915) subjected known elements to x-rays. When Moseley arranged the elements according to increasing atomic numbers and not atomic masses, some of the inconsistencies associated with Mendeleev's table were eliminated. At age 28, Moseley was killed in action during World War I and as a direct result Britain adopted the policy of exempting scientists from fighting in wars. Shown below is a periodic table from 1930. -
Seaborg
Starting with plutonium in 1940, Seaborg discovered transuranium elements 94 to 102 and reconfigured the periodic table by placing the lanthanide/actinide series at the bottom of the table. -
Seaborg
In 1951 Seaborg was awarded the Nobel Prize in chemistry and element 106 was later named seaborgium (Sg) in his honor. -
The Modern Periodic Table
The last major change to the periodic table resulted from Glenn Seaborg's work in the middle of the 20th century. New additions to the periodic table are WOMANIUM (WO) and MANIUM (XY).