Final answer:
Chemists sort elements into groups on the periodic table based on electron configuration and atomic number, which determine the elements' chemical reactivity and properties.
Step-by-step explanation:
Chemists used electron configuration, among other characteristics, to sort elements into groups on the periodic table. Dmitri Mendeleev, the creator of the periodic table, organized elements based on their atomic number, which is directly linked to an element's electron configuration. The configuration of electrons impacts an element's chemical properties, including its chemical reactivity. While Mendeleev initially considered atomic mass in arranging the elements, the modern periodic table is primarily ordered by atomic number, revealing a periodic recurrence of elements with similar chemical properties in defined groups.
The periodic table allows scientists to predict the behavior of elements and their potential to bond and interact with other elements. Elements in the same group have similar valence electron configurations, which is why they exhibit similar chemical reactivity, making the periodic table an invaluable tool for chemists.