Most nitrogen atoms have seven protons and seven neutrons, so their atomic mass is 7 + 7 = 14.
The fact that it has seven protons is what makes it nitrogen.
To the left side of each C (C is the symbol for Carbon) are two numbers, the bottom number indicates the Atomic Number or the number of protons in the nucleus.
Since all the atoms are carbon, they should all have an Atomic Number of 6.
To understand this process we must first understand a little bit about the atoms themselves and how they get their names.Most carbon atoms have six positively charged protons and six uncharged neutrons.Three of the Carbon isotopes (C) are found in nature.The rest of the carbon isotopes are only of laboratory interest.
The top number is the Mass Number for each isotope.The Mass Number for any isotope is the addition of all the protons and neutrons in the nucleus.