Ionic Bonding and Magnetic Model

Problem Oppositely charged ions are attracted in rock salt crystal (Na+ and Cl-), similarly charged ions repel each other (Na+ and Na+, Cl- and Cl-). The attraction of all ions in salt crystals can be explained by the balance of attraction and repulsion forces. It is difficult to create such a model showing electric forces. It is, however, possible to implement a model for demonstration purposes with a balance of magnetic attraction and repulsion forces which thereby simulates a two-dimensional crystal. 

Material Round permanent magnets (10 mm), synthetic cover (5 mm for large discs and 2 mm for small discs), flat wooden box with see-through plexiglas. 

Procedure Place the large discs with their north pole facing upwards, they repel each other. Place the small discs with their north pole facing downwards, they also repel each other. Shake all discs in the closed box on the overhead projector, observe their arrangement. 

Observation Large and small discs attract each other. In the arrangement each large disc is surrounded by four small discs and each small disc surrounded by four large ones (see Fig. 5.19). This structural model can be compared to one layer of the sodium chloride structure. Similarly, salt structures gain stability from the balance of electric attraction and repulsion forces, in relation to the magnets there are magnetic forces. 

Tip If possible, separate the small and large magnets from each other before every new experiment one kind of magnet on one side of the box and the other kind on the opposite side. After separating them, the experiment can be repeated with the same observation. 

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