- You may be looking for atomic weight.
Atomic mass was a property of elements.
An Entity altered the atomic mass of hydrogen within the Iarcho's star, killing the species. (PROSE: From Eternity)
Silver had an atomic mass of 107.870. (PROSE: Wolfsbane)
When Martin Stowe asked for Romana I's number, she did not understand which number and asked if he meant atomic mass. (PROSE: The Glarn Strategy)
The Void Ship had no measurable heat, radiation or atomic mass. (TV: Army of Ghosts)