Chemistry Regents Practice Test 2025 – Complete Prep Resource

The periodic table organizes elements by increasing atomic number, which is the number of protons found in the nucleus of an atom of that element. This property is fundamental because it determines the chemical identity of an element and its place in the periodic table. Elements are arranged in such a way that those with similar properties are grouped together in columns, or groups; this organization reflects the periodic nature of their chemical properties as they change with increasing atomic number.

Atomic weight and mass number are related concepts, but they do not provide the same systematic organization as atomic number does. Atomic weight can vary due to isotopes, and mass number is not as consistent across elements for ordering them effectively. While chemical reactivity is an important property, it is not the primary factor for arranging the periodic table; rather, it is a consequence of the atomic structure defined by atomic number. Overall, the arrangement by increasing atomic number ensures that the trends in elemental properties, such as electronegativity and ionization energy, can be observed clearly.