1. Isotope Atoms that have the same number of p +, but different numbers of n o

3. Atomic Mass Carbon – 12 is reference isotope Assigned a mass of exactly 12 amu amu = atomic mass unit Atomic mass is not a whole number (mass number is a whole number mass number = p + + n o ) Atomic mass is seen on the Periodic Table

4. Why is atomic mass not a whole number? In nature most elements occur as a mixture of 2 or more isotopes. Each isotope has a fixed mass and a natural percent abundance Atomic mass – a weighted average mass of the atoms in a naturally occurring sample of an element.

5. Hydrogen- 3 isotopes Hydrogen – 1 99.985% Hydrogen – 2 (deuterium) Trace amounts Hydrogen – 3 (tritium) Trace amounts Weighted average mass of these isotopes gives a atomic mass of 1.008 amu.

7. Calculating Atomic Mass Information needed: 1.Number of stable isotopes 2.Atomic mass of each isotope 3.The natural percent abundance expressed in decimal form.

8. Steps for Calculating Atomic Mass 1.Multiply the atomic mass of each isotope by its percent abundance changed to decimal form. 2.Add the products of each calculation together for the final answer.

9. Practice problem 1 Calculate the atomic mass of Gallium using the following information. Isotope Atomic Mass Percent Abundance Gallium – 69 68.926 amu 60.108 % Gallium – 71 70.925 amu 39.892%

10. Practice problem 2 Calculate the atomic mass for Argon: Isotope Atomic Mass Percent Abundance Argon – 36 35.978 amu 0.337% Argon – 38 37.963 amu 0.63% Argon – 40 39.962 amu 99.066%

11. Uses of Isotopes Carbon – 14 archeological dating Iodine – 131 treatment of thyroid disease Cobalt – 60 treatment of cancer

12. assignment Read pg 114-116 Complete questions 25-33 on page 119 Video clip http://app.discoveryeducation.com/search #Ntt=isotopes&Ntk=Allhttp://app.discoveryeducation.com/search #Ntt=isotopes&Ntk=All