What constant is approximately 6.022 × 10^23 per mole?

The constant that is approximately 6.022 × 10^23 per mole is the Avogadro constant. Its exact SI value is 6.02214076 × 10^23 mol⁻¹, representing the number of specified elementary entities associated with one mole. Those entities may be atoms, molecules, ions, electrons, or other specified particles.

The constant connects the microscopic world of individual particles with laboratory-scale amounts of substance. One mole of water contains approximately 6.022 × 10^23 water molecules, while one mole of carbon contains the same number of carbon atoms. The particles differ in mass, but the count is the same.

The constant is named after Italian scientist Amedeo Avogadro, who proposed in 1811 that equal volumes of gases under the same conditions contain equal numbers of molecules. The mole was redefined in the SI system effective 20 May 2019, making the numerical value exact rather than experimentally determined. A common mix-up is the gas constant, which relates pressure, volume, temperature, and amount of gas, while the Planck and Boltzmann constants belong to quantum physics and statistical mechanics.