The Avogadro constant, also known as Avogadro's number, is a fundamental value in chemistry that represents the number of particles, usually atoms or molecules, in one mole of a substance. Its approximate value is 6.022 \times 10^23. This constant allows scientists to convert between the mass of a substance and the number of particles it contains, facilitating calculations in chemical reactions. Named after the Italian scientist Amedeo Avogadro, this constant is crucial for understanding the relationships between the amount of a substance and its properties. It plays a key role in the ideal gas law and stoichiometry, helping to predict how substances interact in chemical processes.