RHYS LEWIS, AHS, DECD, UNISA / ANIMATE4.COM / SCIENCE PHOTO LIBRARY RHYS LEWIS, AHS, DECD, UNISA / ANIMATE4.COM / SCIENCE PHOTO LIBRARY
Triads in the periodic table. Animation showing examples of triads, sets of three elements within a group in the periodic table. The historic definition of a triad, as discovered from 1829 by German chemist Johann Wolfgang Dobereiner (1780-1849), was that for a particular property the middle element of the three would have a value that was the average of the other two elements. This early discovery of trends in chemical properties laid the groundwork for the development of the modern periodic table. The five triads shown in this animation are atomic weight triads: Li-Na-K (lithium, sodium, potassium); Ca-Sr-Ba (calcium, strontium, barium); P-As-Sb (phosphorus, arsenic, antimony); S-Se-Te (sulphur, selenium, tellurium); and Cl-Br-I (chlorine, bromine, iodine).
Model release not required. Property release not required.