1. Chapter 3 Atoms and Elements 3.5 Isotopes and Atomic Mass 1 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

2. Isotopes are atoms of the same element have different mass numbers have same number of protons but different numbers of neutrons 2 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

3. Atomic Symbols and Subatomic Particles 3 Examples of number of subatomic particles for atoms: Atomic symbol 16 31 65 O P Zn 8 15 30 8 p + 15 p + 30 p + 8 n16 n 35 n 8 e - 15 e - 30 e - Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

4. Atomic Symbols for Isotopes of Magnesium 4 Mass Numbers Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

5. Atomic Symbols for Isotopes of Magnesium 5 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

6. Learning Check 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 the following: 6 Isotope 12 C 13 C 14 C protons neutrons electrons Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

7. Solution 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 the following: 7 Isotope 12 C 13 C 14 C protons666 neutrons678 electrons666 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

8. Learning Check Write the atomic symbols for atoms with the following subatomic particles: A. 8 protons 8 neutrons 8 electrons B. 17 protons 20 neutrons 17 electrons C. 47 protons 60 neutrons 47 electrons 8 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

9. Solution Write the atomic symbols for atoms with the following subatomic particles: A. 8 protons 8 neutrons 8 electrons B. 17 protons 20 neutrons 17 electrons C. 47 protons 60 neutrons 47 electrons 9 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

10. Learning Check 1. Which of the pairs are isotopes of the same element? 2. In which of the pairs do both atoms have 8 neutrons? A. B. C. 10 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

11. Learning Check 1. Which of the pairs are isotopes of the same element? B. 2. In which of the pairs do both atoms have 8 neutrons? C. 11 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

12. Atomic Mass Atomic mass is the weighted average of all naturally occurring isotopes of that element number on the periodic table below the chemical symbol with two decimal places 12 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

13. Calculating Atomic Mass To calculate atomic mass, use an experimental percent abundance of each isotope of the element multiply the percent abundance by the atomic mass of that isotope sum the total mass of each isotope 13 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

14. Calculating Atomic Mass To calculate atomic mass of Cl, use experimental data for both isotopes of Cl: Isotope atomic mass x % abundance 35 Cl 34.97 amu x 75.76 = 26.49 amu 100 37 Cl 36.97 amu x 24.24 = 8.962 amu 100 Atomic mass of Cl = 35.45 amu 14 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

15. The Atomic Mass of Some Elements 15 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

16. Learning Check Lithium consists of two naturally occurring isotopes, 6 Li and 7 Li. Use the periodic table to predict which isotope is the most prevalent one. Periodic table atomic mass of lithium is 6.941 amu. 16 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

17. Solution Lithium consists of two naturally occurring isotopes, 6 Li and 7 Li. Use the periodic table to predict which isotope is the most prevalent one. Periodic table atomic mass of lithium is 6.941 amu. 6 Li and 7 Li Since the total atomic mass of 7 Li is closer to 7, the mass number of 7 Li, the most prevalent isotope is 7 Li. 17 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

18. Learning Check Gallium is an element found in lasers used in compact disc players. In a sample of gallium, there is 60.10% of 69 Ga (atomic mass 68.926) atoms and 39.90% of 71 Ga (atomic mass 70.925) atoms. What is the atomic mass of gallium? 18 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

19. Solution 69 Ga 68.926 amu x 60.10 = 41.42 amu (from 69 Ga) 100 71 Ga 70.925 amu x 39.90 = 28.30 amu (from 71 Ga) 100 Atomic mass Ga = 69.72 amu 19 31 Ga 69.72 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.