Ionization Definition - When one atom loses or gains an electron, the process is called ionization. This process involves a complete transfer of electrons between atoms. A classic example of ionization is that of sodium (Na) and chlorine (C1).
First, in order to visualize the changes that take place in a sodium atom, you must understand its structure. Sodium has an atomic number of 11 (in other words, it has 11 protons). It also has 11 electrons, so it has a net charge of 0. According to what we have learned so far, its first energy level will contain 2 electrons, and there will be 8 in the second. The third energy level, then, will contain only 1 electron. In order to have a stable structure, with an outermost energy level containing 8 electrons, would it be easier to lose 1 electron or to gain 7? Obviously, it is easier to lose 1, and that is what sodium does. As a result, it now becomes an ion having 11 positive charges and only 10 negative charges. The atom's net charge (protons minus electrons) is plus 1, so in chemical shorthand the notation for this charged atom is now Na+, since it is an ion.
Chlorine, on the other hand, has 17 protons and 17 electrons. Like sodium, it has a net charge of 0. There are 2 electrons in its first energy level, 8 in its second, and 7 in its third. Chlorine too requires an outer energy level containing 8 electrons, and thus it must gain 1 electron or lose 7. It most often gains 1, so it also becomes an ion. When it gains that extra electron to fill its valence orbital, it has 17 (+) charges in its nucleus, but it has 18 electrons for 18 (-) charges. The atom, now an ion, has a net charge of minus 1, written as C1- and called a chloride ion.
Thus sodium's electron is transferred to chlorine. Because these two ions now have opposite charges, they are electrostatically attracted to one another. This attraction is called an ionic bond and the result is the compound NaC1, which is common table salt.
Ionic bonds are relatively weak. As a result they can be broken when placed in water, because water pushes the atoms apart. When the atoms are separated, they are said to dissociate to become freeions. The relative ease with which ionic bonds dissociate is important in living things, because an ionic solution (a uniform mixture of two or more
| types of molecules), often called an electrolytic solution, conducts electric current. What is more, as we will see in later chapters, the movement of ions into and out of cells is a very necessary process in sustaining life. (Source: Avila, Vernon L. Biology : Investigating Life On Earth Jones and Bartlett/Bookmark Series in Biology) |
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