Isotopes

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