Answer:
Because there exist nuclei with with 7 protons and MORE OR LESS than 7 neutrons; that is nitrogen possesses a number of ISOTOPES.
Explanation:
If a nucleus possesses 7 protons, 7 fundamental positive particles, it is by definition a nitrogen atom. The most abundant isotope (as they are called) is
14
N
, however, there exist isotopes where the nitrogen nucleus contains more than 7 neutrons. If there are 8 neutrons, fundamental neutral particles, we have the isotope
15
N
. This isotope is still nitrogen (why? because it has 7 protons) but it masses more than the regular isotope.) and its chemistry is still the same. The atomic mass of nitrogen is thus the weighted average of the individual isotope.
