Ions are formed when atoms lose or gain electrons in order to achieve a stable electron configuration, often resembling that of noble gases.

Atoms consist of protons, neutrons, and electrons. The protons and neutrons reside in the nucleus of the atom, while electrons orbit the nucleus in defined energy levels. The stability of an atom is primarily influenced by its electron configuration. Atoms aim to fill their outermost energy level, which leads to the most stable configuration. This stable state is typically reached when there are eight electrons in the outermost energy level, a condition referred to as the octet rule.

To achieve this stable configuration, atoms can either gain or lose electrons, resulting in the formation of ions. When an atom loses one or more electrons, it becomes a positively charged ion, known as a cation, because it then has more protons than electrons. Conversely, when an atom gains one or more electrons, it becomes a negatively charged ion, called an anion, as it now possesses more electrons than protons.

The likelihood of an atom gaining or losing electrons is significantly influenced by its position in the periodic table. Elements located on the left side, such as sodium ($Na$) and potassium ($K$), typically lose electrons and form cations. This tendency arises because they have fewer electrons in their outer energy level, making it easier to lose these electrons than to gain enough to fill the level. In contrast, elements on the right side of the periodic table, such as chlorine ($Cl$) and oxygen ($O$), are more inclined to gain electrons and form anions. These elements have nearly full outer energy levels, so it is more advantageous for them to acquire a few additional electrons to achieve a complete energy level.

In summary, ions are created through the loss or gain of electrons as atoms endeavor to achieve a stable electron configuration. This process is guided by the octet rule and the atom’s position within the periodic table.