Othmer Library of Chemical History
Science History Institute
315 Chestnut Street
Philadelphia, PA 19106
Monday - Friday
10:00 a.m. - 4:00 p.m.
The Periodic table is a graphic layout that demonstrates the relationship among the elements in order of increasing atomic number. The table illustrates periodic law in the groups of elements with similar properties. The quick buildup of chemical and elemental knowledge during the 19th century meant that a classification was necessary.
There have been and continue to be many different graphic representations of the elements and periodic law but the one based on Mendeleev’s has become standard with its simplistic layout. It is easy to recognize and easy to memorize making it the go to for educators and professionals. Some of the other tables have been round, triangle, swirling and even 3-dimensional.
Periodic Law is the idea that chemical and physical properties of the elements recur periodically when the elements are arranged in the order of their atomic weights. Within the periodic table there are 7 horizontal rows called Periods and 18 vertical columns called Groups. The periodic law has been found to display relationships of many different properties of the elements within these periods and groups. Some of these are physical properties such as melting and boiling points, densities, crystal structures, hardness, electrical conductivity, heat capacity and thermal conductivity, and chemical properties such as reactivity, acidity or basicity, valence, polarity and solubility.