Which term describes the horizontal rows on the periodic table?

The term that describes the horizontal rows on the periodic table is "periods." In the context of the periodic table, each period corresponds to the principal energy levels of the electrons in an atom. As you move from left to right across a period, the atomic number increases, and elements generally show a progression in properties. This organization helps illustrate periodic trends, such as electronegativity and atomic radius, throughout the table. Understanding periods is essential for grasping how elements behave and are categorized based on their electron configurations. This knowledge can be particularly useful when predicting chemical behavior and reactivity among the different elements listed in each row.