Then there is the atomic number atomic mass number.

As for Dalton, his name lives on as alternate designation for the atomic mass unit or amu.

He soon had a table of 21 elements arranged by atomic mass, which he presented in a scientific paper the following month.

With a relative uncertainty of eight parts per trillion, this is the most precise mass value measured directly in atomic mass units.

All units of mass-thekilogram, the atomic mass unit, and even America's sweetheart, the pound-canbe calculated from that value of Planck's constant.

Alas, Mendeleev's table was based on atomic mass rather than atomic number, so details like the placement of tellurium and iodine didn't work out.

To separate tiny atomic masses requires something that can spin at tens of thousands of rotations per minute.