Isotope …, "m" are the atomic masses of each individual isotope, and "x", …, "x" are the relative abundances of these isotopes. Several applications exist that capitalize on properties of the various isotopes of a given element. Isotope separation is a significant technological challenge, particularly with heavy elements such as uranium or plutonium. Lighter elements such as lithium, carbon, nitrogen, and oxygen are commonly separated by gas diffusion of their compounds such as CO and NO. The separation of hydrogen and deuterium is unusual because it is based on chemical rather than physical properties, for example in the Girdler sulfide process.
Standard atomic weight major source of argon is the decay of in rocks, will be the dominant isotope. Such locations include the planets Mercury and Mars, and the moon Titan. On Earth the ratios of the three isotopes Ar : Ar : Ar are approximately 5 : 1 : 1600, giving terrestrial argon a standard atomic weight of 39.948(1). This atomic weight is larger than that of the next element potassium, causing confusion in the days when the places of elements in the periodic table was largely determined according to atomic weight. However, such is not the case in the rest of the