The Atom 

 Atoms are the building blocks of matter. They are the smallest particles of an element that still have the element’s properties. Elements, in turn, are pure substances—such as nickel, hydrogen, and helium—that make up all kinds of matter. All the atoms of a given element are identical. They are also different from the atoms of all other elements.

 Although atoms are very tiny, they consist of even smaller particles. Three main types of particles that make up all atoms are:

Proton:

  A positively charged particle located in the nucleus.  The charge of a proton is 1.6E-19 coulombs and a mass of 1.673E-27 kg.   The atomic number of an atom is equal to the number of protons located in nucleus.  

Neutron:  

   A neutrally  charged particle located in the nucleus.  The charge of a neutron is 0 coulombs and a mass of 1.674E-27 kg.  Neutrons are unstable particles that survive about 15 minutes if it isn't bounded to proton. 

Electrons: 

  A negatively charged elementary particle normally not located in the nucleus.  The charge of an electron is -1.6E-19 and a mass of 9.109E-31 kg.  Electrons are normally not considered when solving nuclear physics problems.

Stable Carbon 

For stable carbon (carbon 12) we would express it like this  

 And if we needed to determine the number of neutrons in carbon we subtract the atomic number from the atomic mass number

12 nucleons - 6 protons = 6 neutrons 

Unstable (radioactive) Carbon 

for unstable radioactive carbon (carbon 14) we express it like this 

And if we needed to determine the number of protons in carbon 14  we subtract the atomic number from the atomic number 

14 nucleons - 6 protons = 8 neutrons

an isotope