I. Isotopes: Atoms with the same number of protons but different numbers of neutrons -Written with the atomic # on the top left, atomic mass # on the top right II. Example: Carbon -Carbon-12: 6p+, 6e-, 6n -Carbon-13: 6p+, 6e-, 7n -Carbon-14: 6p+, 6e-, 8n (used for carbon dating) III. Calculating Atomic Mass Numbers -The atomic mass number of carbon is 12.0107 -The abundance of Carbon-12 on Earth is 98.9% -The abundance of Carbon-13 on Earth is 1.1% -The abundance of Carbon-14 on Earth is 0% -(12 AMU x .989) + (13 AMU x .011) + (14 AMU x 0) = 12.011 (about 12.0107) IV. Bottom Line -If you change the protons, you change the element -If you change the electrons, you change the ionic charge -If you change the neutrons, you change the isotope |