An ionic bond is an electrostatic attraction between charged particles. Recall from Chapter 2 that protons, which are positive, and electrons, which are negative, are attracted to one another. Larger charged particles, which are called ions, behave analogously. In order to ionize, or become charged, an atom must gain or lose valence electrons, thereby creating an imbalance between the number of positively-charged protons and negatively-charged electrons that it contains. The ionization process will be explained in greater detail in the next section of this chapter. Cations are positively-charged ions that are most often formed when metals lose valence electrons. Non-metals gain valence electrons to form anions, which are negatively-charged ions. Metalloids are unable to gain or lose valence electrons and, therefore, cannot form ions or form an ionic bond. Ions can also exist in a polyatomic, or multi-atom, form, as will be discussed in a later section of this chapter.
An ionic bond is produced when a cation exists in close physical proximity to an anion, creating an electrostatic attractive force. Therefore, based on the information in the previous paragraph, ionic bonds can be formed by combining
- a metal, which will ionize to form a cation, and a non-metal, which will ionize to form an anion,
- a metal, which will ionize to form a cation, and a polyatomic anion,
- a polyatomic cation and a non-metal, which will ionize to form an anion, or
- a polyatomic cation and a polyatomic anion.
The next several sections of this chapter will explain how atoms ionize, as well as how the resultant ions interact to form ionic compounds, and will present the processes for determining the chemical formulas and the chemical names of these ionic compounds.