The atomic mass of argon is 39.948 u.
The atomic mass of an element is the average mass of its atoms. It is expressed in atomic mass units (amu), which are defined as one-twelfth of the mass of a carbon-12 atom.
Argon has three naturally occurring isotopes: argon-36, argon-38, and argon-40. The atomic masses of these isotopes are 35.96754 u, 37.96272 u, and 39.96249 u, respectively. The abundance of each isotope in nature is as follows:
- Argon-36: 0.00337
- Argon-38: 0.00632
- Argon-40: 0.99031
The atomic mass of argon is calculated by averaging the atomic masses of its isotopes, weighted by their natural abundances. This gives a value of 39.948 u.