What two elements have lower average atomic masses than atomic numbers?

Atomic masses tend to rise in the same order as atomic numbers. Elements with multiple isotopes can violate this trend.





Robert is on the right track in interpreting your flawed question.





Elements in violation are:





Potassium (39.10) lower than Argon (39.96) before it.





Nickel (58.70) lower than Cobalt (58.93) before it.





Tellurium (127.60) HIGHER than Iodine (126.90) after it.





The two elements you seek are Potassium and Nickel.





Tellurium does not qualify because it is out of place to the heavier side, not the lighter side. In this case Iodine is the ';anchor';, because it has only one isotope. It is in the correct order. It is the Tellurium that has a higher percentage of its heavier isotopes than would be expected.What two elements have lower average atomic masses than atomic numbers?
Since the atomic number counts the protons in the nucleus and the atomic mass counts the number of protons and neutrons, no elements have lower atomic masses than atomic numbers. I think the question you want answered is ';what two elements have lower atomic masses than the elements just after them (with higher atomic numbers)? These are potassium and tellurium.What two elements have lower average atomic masses than atomic numbers?
I think this may be a trick question. The atomic number is the number of protons in an atom. The weight is the number of protons plus the number of neutrons. Thus the atomic mass can never be lower than the atomic number (just the same if there are no neutrons).
herm i may be going insane but your question may be false,
none that i know of, most elements on the periodic table should have twice or more atomic mass than number