Ionic bonding in sodium chloride

NaCl in a 3-dimensional crystal

The thumbnail image to the right depicts a ball and stick modelof sodium chloride, NaCl.

= Na⁺ = Cl^-

We observe that each Na⁺ ion is surrounded by 6 Cl^- ions. Similarly, each Cl^- ion has 6 Na⁺ ions as its nearest neighbour. The electrostatic forces of attraction between ions of opposite charge are the ionic bonds.

If we inspect the ball and stick model closely, in a repeating unit of the structure, the ratio of Na+ ion to Cl- ion is 1:1. Therefore, the simplest unit of this ionic compound is NaCl.

In the sodium chloride crystal structure, every cation has anions around it, and every anion is surrounded by cations. Click on the thumbnail image to view an animation of the formation of a NaCl crystal. The small circles are the sodium ions in solution. The larger circles are the chlorine ions in solution.

Click to view an animation of sodium and chlorine ions in solution forming a seed crystal, which gradually grows as more atoms are removed from solution and bonded to its surface.

Lewis electron dot symbol to describe ionic bonding in sodium chloride

The formation of sodium chloride involves sodium metal, Na and chlorine gas, Cl₂. The reaction can be thought of involving the following simultaneous processes:

1. The oxidation of sodium metal

Sodium atoms lose its outer-shell electron to become a sodium ion, (i.e. cation). The sodium metal is said to be oxidized. The diagram below shows two sodium atoms undergoing oxidation.

Sodium ion 1:

Sodium ion 2:

1. The Reduction of Chlorine Gas

Chlorine is a diatomic element. The covalently bonded Cl₂ molecule gains two electrons to become two chloride ions, (i.e. anions). Chlorine is said to be reduced.

Combining the above oxidation and reduction processess, the overall effect is the transfer of ONE electron from sodium to chlorine.

The oppositely charged sodium and chloride ions attract each other and ionic bonds are formed. In the solid state, each cation is surrounded by anions, and each anion is surrounded by cations. These ions arrange themselves in a 3-dimensional crystal. The simplest ratio of Na⁺ : Cl^- is 1:1. The simplest formula for this ionic compound is NaCl.