What is the periodic table organized by?

The periodic table is organized by increasing atomic number, which represents the number of protons in an atom's nucleus. This arrangement not only helps in categorizing the elements but also reflects the periodic trends and properties of the elements.

As you move across a period in the periodic table from left to right, the atomic number increases, which results in a systematic change in properties such as electronegativity, atomic radius, and ionization energy. The organization by atomic number rather than atomic mass resolves discrepancies that were present in early periodic tables, where some elements were improperly categorized based on mass rather than their actual atomic structure.

This systematic organization allows for a deeper understanding of how different elements interact chemically and physically, which is essential for studying chemistry.