This simulation shows how regular structures are spontaneously created by mutual interaction between particles. Here, positively and negatively charged particles are moving on a two dimensional surface. Over short distances they repel each other; over longer distances, coulomb's force attracts the particles to one another (similarly charged particles repel, unequally charged particles attract one another). This interdependency alone creates numerous different structures. Although this model is only a simplification of nature, the behaviour is virtually prototypical for many chemical reactions.
In the animation one can change the parameters, such as the charges and the proximity rejection forces. A small chemical laboratory!