1. The fundamental subatomic particles which make up the atom are: , and 2. The nucleus is composed of the particles and 3. The mass of an electron is approximately what fraction the mass of a proton? 4. The atomic number is equal to the number of in the nucleus. 5. Since the mass of the electron is so small as to be negligible, almost the entire mass of the atom is found in the of the atom. 6. Two atoms of the same element which have different masses are called 7. The mass of the atom is the sum of the number of and in the nucleus. 8. The difference between the mass number and the atomic number of a particular atom gives the number of in the nucleus of that atom