The Development and Evolution of the Periodic Table

• Date of Origin: The periodic table was developed in $1869$ by Dmitri Mendeleev, originally consisting of $63$ elements.

• Organizational Principles: Mendeleev arranged elements into groups by similar properties and ordered them by increasing atomic mass.

• Predictive Gaps: He identified gaps for undiscovered elements, predicting their properties accurately.

Challenges to Mendeleev's Arrangement

• Some elements like Tellurium ($Te$) and Iodine ($I$) appeared in the wrong order based on atomic mass, so Mendeleev prioritized properties over mass when arranging them.

The Role of Henry Moseley and Atomic Number

• In $1913$, Henry Moseley rearranged Mendeleev's table by atomic number instead of atomic mass, resolving previous discrepancies.

Evolution of the Modern Periodic Table

• By $1913$, there were $81$ known elements; today there are $108$, based on Moseley's framework.