Why might scientists who study changes of state build models showing the arrangement of particles in a substance?

Building models showing the particle arrangement of the substance would help clearly understand the characteristics and behaviors of certain substance at a specific state. Also, this would help ascertain the state/nature of a substance. For example, particles in a solid state are arranged in a tightly packed manner normally with a distinct regular pattern while substances in a liquid and gaseous states doesn't have any particular arrangement at all.

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