**Avogadro's number, also called Avogadro's law, creates a constant value for different gases, regardless of weight and structure, which makes it a foundational law in chemistry.** Italian scientist Amedeo Avogadro created his theory after observing that gases have equal volumes at given temperatures and pressures, and therefore contain the same number of molecules. Avogadro's number, written mathematically as 6.022 x 10^{23}, demonstrates the number of molecules present in any gas within the fixed volume of 22.41L.

Avogadro proposed his theory in 1811, although his law did not gain widespread attention until the late 1850s, when Stanislao Cannizzaro, another Italian chemist, used Avogadro's law as a foundational base to demonstrate a complete and rational system of chemistry.

In addition to existing as a mathematical equation, Avogadro's law contains a written statement with a theory and rationale. The statement asserts that different gases, regardless of weight, have an equal number of molecules in a given fixed volume. Avogadro explains this phenomenon through the theory of kinetic gases, which bases its principles on the assumption of an ideal gas.

Avogadro's law holds true throughout the field of chemistry, provided equations use real gases with relatively low pressures and high temperatures. Avogadro's law also explains the volume occupied by gases, which is the same for all real gases based on a fixed temperature and pressure.