A pattern of repeating order is called periodicity. Since the 1830s chemists explored the repeating patterns of properties associated with the chemical elements and their compounds, and from these studies the modern 'medium form' periodic table emerged.

Which IsThe Best Periodic Table Formulation To Use?

There are many, many formulations of the periodic table – just see the previous page of this web book – but the formulation that most clearly exhibits and displays periodicity is the conventional medium form periodic table, as displayed by WebElements:


The medium form PT is derived from the long form periodic table (the transformation is explained in more detail in two place, an entry in the PT database and more fully in a paper, published in Foundation of Chemistry:

Likewise, the medium form periodic table can be reduced to a short form PT, showing just the main group elements:

In different situations, periodicity is can be mapped to the long form periodic table, at other times medium or short form periodic tables are employed.



Wikipedia periodicity


Atomic Number:

atomic number









Database of Periodic Tables
Binary Compounds

© Mark R. Leach 1999-

Queries, Suggestions, Bugs, Errors, Typos...

If you have any:

Suggestions for links
Bug, typo or grammatical error reports about this page,

please contact Mark R. Leach, the author, using

This free, open access web book is an ongoing project and your input is appreciated.