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.

Avogadro’s Law

Avogadro’s Law, fundamental law of chemistry stating that under identical conditions of temperature and pressure, equal volumes of gases contain an equal number of molecules. The law was first proposed as a hypothesis by the Italian physicist Amedeo Avogadro in 1811. Italian chemists and physicists continued to develop this hypothesis, and in the 1850s, largely through the efforts of the Italian chemist Stanislao Cannizzaro, Avogadro's law was universally accepted.