1. …AND THE AVERAGE ATOMIC MASS Isotopes

2. PG 88 GENERAL- ATOMS OF THE SAME ELEMENT BUT HAVE DIFFERENT AMOUNTS OF NEUTRONS IN THE NUCLEUS PAGE 54 PRE AP ATOMS WITH SAME NUMBER OF PROTONS BUT DIFFERENT NUMBERS OF NEUTRONS Isotopes

3. EACH ISOTOPE HAS A DIFFERENT MASS DUE TO THE DIFFERENT AMOUNTS OF NEUTRONS IN THE NUCLEUS. WE CAN NOT LIST EVERY ISOTOPE ON THE PERIODIC TABLE SO WE HAVE HAD TO TAKE THE AVERAGE WEIGHTED MASS TO DISPLAY Mass is affected.

4. TO FIGURE THE AVERAGE MASS THAT IS LOCATED ON THE PERIODIC TABLE ONE MUST - LIST THE ISOTOPES AND THEIR PERCENTAGE OF ABUNDANCE - MULTIPLY EACH % BY THAT ISOTOPES MASS AND DIVIDE BY 100 TO GET THAT ISOTOPES RELATIVE MASS - FINALLY ADD THE RELATIVE MASSES FROM ALL ISOTOPES TOGETHER TO GET THE AVERAGE WEIGHTED MASS FOR THAT ELEMENT How is average weighted mass figured?

5. PURE CARBON CARBON-12 IS 98% CARBON-13 IS 1.11% THE MASS OF CARBON 12 IS 12.000AMU THE MASS OF CARBON 13 IS 13.004 C12=(12.000X98%)/100 + C13 (13.004X 1.11%)/100 =11.76 +.1443=11.90 (12) Example