Ionic Bond

Ionic Bonding: Salt

The bond (left) between the atoms in ordinary table salt (sodium chloride) is a typical ionic bond. In forming the bond, sodium becomes a cation (a positively charged ion) by “giving up” its valence electron to chlorine, which then becomes an anion (a negatively charged ion). This electron exchange is reflected in the size difference between the atoms before and after bonding. Attracted by electrostatic forces (right), the ions arrange themselves in a crystalline structure in which each is strongly attracted to a set of oppositely charged “nearest neighbors” and, to a lesser extent, all the other oppositely charged ions throughout the entire crystal.

Oppositely charged ions have a strong mutual electrostatic attraction when brought together, but, if brought too close, the electron clouds repel each other. Thus, a pair of mutually attracted ions will maintain a certain distance from each other. This distance is called the bond length, and the electrostatic attraction of the ions constitutes an ionic (or electrovalent) bond. Ionic bonds are very common and are exemplified by table salt, in which a sodium ion attracts a chloride ion to form Na⁺Cl^- or, as usually written, NaCl. Calcium ions (Ca²⁺) and chloride ions (Cl^- ) combine in a one-to-two ratio to form calcium chloride, CaCl₂. The total charge on each combination of ions, NaCl and CaCl₂, is neutral, or zero.