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.


Valence (chemistry), in chemistry, a number representing the capacity of a single atom or radical to combine with other atoms or radicals. The value is an expression of the number of electrons that an atom can give to or accept from another atom or radical during a chemical reaction.