The Logic Behind the Periodic Table’s Design

Today, the modern periodic table is as instantly recognizable as a map of the world—but this intuitive layout was once a radical idea. In 1869, Dmitri Mendeleev began organizing the known chemical elements during a train journey, treating it almost like a puzzle. He grouped elements by similar properties but quickly noticed anomalies that disrupted the emerging patterns.

Rather than abandoning his idea, Mendeleev boldly adjusted the measured values of certain properties to make the patterns fit more logically. Even more impressively, he predicted the existence of undiscovered elements, leaving blank spaces where he believed they would eventually be found.

His work initially faced skepticism, but when elements were later discovered that matched his predictions, his model gained widespread acceptance. Remarkably, several of the property values he had “corrected” were later confirmed by more accurate measurements to be closer to his estimates than to the original data.

How the Periodic Table Evolves—and Who Updates It

Yes, the periodic table continues to evolve—and those changes are overseen by the International Union of Pure and Applied Chemistry (IUPAC), pronounced "eye-you-pack".

While most of the table remains stable, IUPAC sets rigorous criteria for the discovery of new elements and is responsible for updating the table accordingly. New elements are first given provisional names and symbols. Once confirmed, they receive official names—such as when elements 113, 115, 117, and 118 were validated and renamed (farewell, ununseptium; hello, tennessine).

Even atomic weights, which may seem fixed, are subject to revision. Since 1899, IUPAC’s Commission on Isotopic Abundances and Atomic Weights (CIAAW) has refined these values. For instance, carbon’s atomic weight was listed as exactly 12.00 in 1902—today it’s a range: [12.0096, 12.0116]. These changes reflect improved measurement techniques and natural variations in isotopic abundance across different sample sources.

IUPAC also defines group numbering (1–18), assigns collective names like lanthanoids and actinoids, and continues to study the membership of elements within Group 3.

Aladdin’s Portal to Chemical Element Information

This periodic table page is designed as a gateway into the extensive chemical element data curated by Aladdin. Whether viewing the table or list format, you’ll find links to dedicated summary pages for each element.

Each element’s page offers detailed information, sources, and references—essential for understanding the context and accuracy of its properties.

How Element Properties Vary Across the Periodic Table

At the top of this page, the Display Property feature lets you examine trends in various elemental properties. For many of these, Aladdin provides interactive visualizations and links to dedicated data pages—offering a deeper dive into how properties vary across the periodic table.

• Chemical Group Block
• Plot Atomic Mass
• Standard State
• Electron Configuration
• Oxidation States
• Plot Electronegativity (Pauling Scale)
• Plot Atomic Radius (van der Waals)
• Plot Ionization Energy
• Plot Electron Affinity
• Plot Melting Point
• Plot Boiling Point
• Plot Density
• Year Discovered