Which of these is not a property that changes in periodic trends?

The property that does not change in periodic trends is ionic charge. Unlike atomic radius, electronegativity, and ionization energy, which exhibit distinct trends across periods and down groups in the periodic table, ionic charge remains generally constant for a given element.

Ionic charge is determined by the number of electrons an atom gains or loses during chemical reactions to achieve a stable electron configuration, typically resembling that of the nearest noble gas. For instance, alkali metals (such as sodium) will consistently form +1 ions, while alkaline earth metals (such as magnesium) will consistently form +2 ions. This consistency means that the ionic charge is more of a characteristic of an element rather than a property that varies with its position in the periodic table.

In contrast, atomic radius decreases across a period due to increasing nuclear charge, electronegativity generally increases across a period and decreases down a group, and ionization energy generally increases across a period and decreases down a group. Therefore, while the other properties show significant trends when observing the periodic table, ionic charge remains fixed and does not exhibit the same variation.