Chemistry Regents Practice Test

The arrangement of elements on the Periodic Table is based on what property?

1. Molar mass

2. Mass number

3. Atomic number

4. Density

The correct answer is: Atomic number

The arrangement of elements on the Periodic Table is primarily based on atomic number, which is the number of protons found in the nucleus of an atom of an element. Each element has a unique atomic number that determines its identity and position in the table. As you move across the Periodic Table from left to right, the atomic number increases sequentially, which correlates with the increase in the number of protons and typically reflects the arrangement of electrons in shells around the nucleus. This is essential for understanding the chemical behavior and properties of the elements, as the electron configuration is fundamental to chemical bonding and reactivity. While molar mass, mass number, and density can provide useful information about elements and their isotopes, they do not dictate the organization of the periodic table. Instead, the periodic table is structured in a way that highlights trends in chemical properties, which are more closely related to atomic number than to any of the other properties listed.