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Atomic Masses of Elements

The atomic mass of different elements is not a whole number because it's the *average* of the masses of different "isotopes" of that element. "Isotopes" are different versions of the element, with different number of neutrons but the same number of protons. If a proton is added or removed from an atom, it becomes a different element!

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The TED project was funded in part by the Institute of Education Science (IES), Grant R305H060034, and in part by the National Science Foundation, Grant SBE035442. The ISP Tutor project was funded by IES, Grant R305A170176.

The research reported here was supported by the Institute of Education Sciences, U.S. Department of Education, through Grant R305A170176 to Carnegie Mellon University (Klahr Lab). The opinions expressed are those of the authors and do not represent views of the Institute or the U.S. Department of Education.