Atoms or molecules that lose two electrons usually have a low ionization energy, which means that it takes less energy to remove the second electron compared to the first. For example, elements in Group 2 of the periodic table, such as magnesium (Mg) and calcium (Ca), have a low second ionization energy. When these elements lose their first two electrons, they form ions with a charge of 2+, such as Mg2+ and Ca2+.
On the other hand, gaining two electrons to form a 2- charge is more common in nonmetallic elements, particularly those in Group 16 (also known as the chalcogens), such as oxygen (O) and sulfur (S). When these elements gain two electrons, they form ions with a charge of 2-, such as O2- and S2-.
It's worth noting that the formation of ions with a charge of 2 is not limited to elements. Some polyatomic ions, which are molecules that carry an electric charge, can also have a charge of 2-. A well-known example is the carbonate ion (CO32-), which consists of one carbon atom bonded to three oxygen atoms.
In summary, an ion with a charge of 2 can form when an atom or molecule loses or gains two electrons. The specific elements and circumstances involved determine whether an ion will have a positive or negative charge of 2.
