Clarke Earley, Ph.D.
Department of Chemistry
Kent State University Stark Campus
North Canton, OH 44720
Ionic compounds are formed due to the electrostatic attraction between oppositely charged ion. Ionic compounds consist of
The charge of many elements can be predicted based on their position on the periodic table.
Ionic compounds differ from molecular compounds in several important ways. For example,
Many of the most important features of ionic compounds can be illustrated using NaCl as an example. This compound contains the metal sodium (Na) and the non-metal chlorine (Cl). In ionic compounds, the charges of Na and Cl can be determined by referring to the periodic table (see above), giving:
Atoms are incredibly small. In order for a compound to exist as a stable solid, the total charge must be zero. (Otherwise, the incredible number of charges would give rise to a huge electrostatic repulsive force, which would tear the material apart). In sodium chloride, the +1 charge on the sodium ion is exactly balanced by the -1 charge on the chloride.
The simplest picture of NaCl is a single pair of Na+1 and Cl-1 ions as shown below. However, this diagram suggests that each Na ion is only attached to or surrounded by a single chloride (and vice versa), which is not correct.
A more realistic picture of NaCl can be drawn be imagining that a sodium ion is placed on a flat surface. This ion can then be surrounded by four (4) chloride ions. In turn, each of these chloride ions, is surrounded by four sodium ions. This process can be repeated in two-dimensions as long as ions remain. A small sample of this could look like is shown in the two-dimensional drawing shown below.
However, molecules are not really 'flat' but instead exist in three-dimensions. In ions are placed above and below the layers shown above, a 'three-dimensional' image can be drawn. This image reflects that crystalline structure of sodium chloride.
Note that each layer is 'offset' so that Na+1 ions are not placed on top of each other, but are placed over (or below) Cl-1 ions.