BACK TO atomic-number

atomic mass vs. atomic number

atomic mass

[ uh-tom-ik mas ]
noun
  1. the mass of an isotope of an element measured in units formerly based on the mass of one hydrogen atom taken as a unit or on 1/16 (0.0625) the mass of one oxygen atom, but after 1961 based on 1/12 (0.0833) the mass of the carbon-12 atom.

atomic number

[ uh-tom-ik nuhm-ber ]
noun
  1. the number of positive charges or protons in the nucleus of an atom of a given element, and therefore also the number of electrons normally surrounding the nucleus. Abbreviation: at. no.; Symbol: Z