A Nitrogen atom with 7 protons and 8 neutrons has a mass number of 15 amu. However on the periodic table, the atomic mass for Nitrogen is 14.01. How is this possible?
Because there exist nuclei with with 7 protons and MORE OR LESS than 7 neutrons; that is nitrogen possesses a number of ISOTOPES.
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