PART_6 WHAT IS ATOMIC MASS AND ISOTOPES?Isotope and atomic massIsotopes are atoms that have the same atomic number but different mass numbers due to a change in the number of neutrons.What is the difference between an atom and an isotope?Atoms with the same number of protons but different numbers of neutrons are called isotopes.What is the difference between atomic number mass number and isotopes?Key Terms. mass number: The sum of the number of protons and the number of neutrons in an atom. atomic number: The number of protons in an atom. atomic mass: The average mass of an atom, taking into account all its naturally occurring isotopes.What is an example of an isotope?For example, carbon has six protons and is atomic number 6. Carbon occurs naturally in three isotopes: carbon 12, which has 6 neutrons (plus 6 protons equals 12), carbon 13, which has 7 neutrons, and carbon 14, which has 8 neutrons.