Periodic table - Wikipedia
https://en.wikipedia.org/wiki/Periodic_tableIn 1817, German physicist Johann Wolfgang Döbereiner began to formulate one of the earliest attempts to classify the elements. In 1829, he found that he could form some of the elements into groups of three, with the members of each group having related properties. He termed these groups triads. Chlorine, bromine, and iodine formed a triad; as did calcium, strontium, and barium; lithi…
Periodic Table - Ptable
ptable.comInteractive periodic table showing names, electrons, and oxidation states. Visualize trends, 3D orbitals, isotopes, and mix compounds. Fully descriptive writeups.
Periodic table - Wikipedia
en.wikipedia.org › wiki › Periodic_tableThe periodic table, also known as the periodic table of ( the) ( chemical) elements, is a tabular display of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of chemistry. It is a graphic formulation of the periodic law, which states that the properties of the chemical elements ...