1. Same Element Different Atom- Isotopes All atoms of a particular element are not exactly alike. Some elements have atoms with different masses (isotopes)

2. Learning Objectives You will know what isotopes are You will be able to figure out the number of neutrons for each isotope You will be able to calculate the atomic mass of an element that has different isotopes.

3. Isotope Example 35 Cl 37 Cl17 chlorine - 35 chlorine - 37

4. Isotopes of Carbon Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12 C 13 C 14 C 6 6 6 #P _______ _______ _______ #N _______ _______ _______ #E _______ _______ _______

5. Solution 12 C 13 C 14 C 6 6 6 #P __6___ _ 6___ ___6___ #N __6___ _ _7___ ___8___ #E __6___ _ 6___ ___6___

6. Zinc problem An atom of zinc has a mass number of 65. A.Number of protons in the zinc atom 1) 302) 353) 65 B.Number of neutrons in the zinc atom 1) 302) 353) 65 C. What is the mass number of a zinc isotope with 37 neutrons? 1) 372) 653) 67

7. Solution to Zinc Problem An atom of zinc has a mass number of 65. A. Number of protons in the zinc atom 1) 30 B. Number of neutrons in the zinc atom 2) 35 C. What is the mass number of a zinc isotope with 37 neutrons? 3) 67

8. Atomic Mass Listed on the periodic table Gives the mass of “average” atom of each element compared to 12 C Average atom based on all the isotopes and their abundance % Atomic mass is not a whole number … mass number is a whole number Na 22.99

9. Calculating Atomic Mass Percent(%) abundance of isotopes Mass of each isotope of that element Weighted average = mass isotope 1 (%) + mass isotope 2 (%) + … 100 100

10. Atomic Mass of Magnesium Isotopes Mass of Isotope Abundance 24 Mg =24.0 amu 78.70% 25 Mg = 25.0 amu 10.13% 26 Mg = 26.0 amu 11.17% (24)(.787) + (25)(.1013) + 26(.1117) = 18.888 + 2.5325 + 2.9042 = 24.3 amu