Elements include ions because ions are formed when atoms gain or lose electrons, resulting in a net electrical charge. This process is crucial for the stability and reactivity of elements in chemical reactions. According to the American Chemical Society, approximately 99% of all atoms in the universe are ions, either as free ions or as part of ionic compounds. The formation of ions is driven by the desire of atoms to achieve a stable electron configuration, typically the electron configuration of the nearest noble gas. For instance, sodium (Na) loses one electron to become a sodium ion (Na+), while chlorine (Cl) gains one electron to become a chloride ion (Cl-). This electron transfer allows both elements to achieve a full valence shell, which is more energetically favorable and stable. The periodic table provides a clear pattern of ion formation, with metals generally losing electrons to form cations and non-metals gaining electrons to form anions. This behavior is a fundamental aspect of chemical bonding and is essential for the structure and properties of matter.