一個問題....................

Nitrogen
Atomic Number is 7
Molar mass is 14grams
In an atom of nitrogen, there is 7 protons and 7 neutrons (and 7 electrons),
so the relative mass of the atom of nitrogen can be taken as 14.
In an isotope of nitrogen, there is 7 protons and 8 neutrons (and 7 electrons),
so the relative mass of the atom of nitrogen can be taken as 15.
But in our atmosphere, N14 is more abundant than N15, N14 (99.63%), N15 (0.37%),
so the atomic weight of nitrogen is taken as 14.0067