What is a periodic trend?

A periodic trend refers to a consistent and predictable pattern observed in the properties of elements as you move across a period or down a group in the periodic table. This can include trends in atomic radius, ionization energy, electronegativity, and other physical and chemical properties. For example, as you move from left to right across a period, the atomic radius typically decreases while ionization energy increases due to the increasing effective nuclear charge. Such trends are fundamental to understanding the behavior of elements and predicting how they will react in chemical processes. This predictable nature is what defines a periodic trend, making it a crucial concept in chemistry.