Editing Periodic table (section)

== Historical Development ==

=== Early Attempts ===
The first systematic organization of elements began in the early 19th century:

* 1817: Johann Döbereiner identified chemical triads
* 1863: John Newlands proposed the Law of Octaves
* 1864: Lothar Meyer developed an early version based on atomic volumes

=== Mendeleev's Breakthrough ===
Dmitri Mendeleev published his first periodic table in 1869, making several crucial innovations:

* Arranged elements by atomic weight
* Left gaps for undiscovered elements
* Successfully predicted properties of unknown elements
* Focused on chemical properties rather than physical properties

=== Modern Developments ===
The periodic table continued to evolve through the 20th century:

* 1913: Henry Moseley established atomic number as the fundamental organizing principle
* 1940s: Glenn Seaborg's work on transuranium elements led to the actinide concept
* 1945: Development of the modern form with separate f-block
* 2016: Completion of the seventh period with elements 113, 115, 117, and 118