Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Conduction in Liquid Solutions

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Many substances become ionized when they dissolve in water or in some other liquid. An example is ordinary table salt, sodium chloride (NaCl). When sodium chloride dissolves in water, it separates into positive sodium ions, Na+, and negative chlorine ions, Cl-. If two points in the solution are at different potentials, the negative ions drift toward the positive point, while the positive ions drift toward the negative point. As in gases, the electric current is composed of these flows of opposite charges. Thus, while water that is absolutely pure is an insulator, water that contains even a slight impurity of an ionized substance is a conductor.

Since the positive and negative ions of a dissolved substance migrate to different points when an electric current flows, the substance is gradually separated into two parts. This separation is called electrolysis.