A mass number is the sum of numbers of protons and neutrons in an atom. Therefore, an element with a mass number of 65 and 36 neutrons contains (65 - 36) or 29 protons and is therefore an atom of copper. read more
Isotopes of an element have the same atomic number (number of protons), but different numbers of neutrons. An isotope is named for its mass number. Copper has two stable isotopes found in nature, copper-63 and copper-65. Copper is the only element that has a stable isotope with a mass number of 65. read more