General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.1 Chapter 3 Atoms and Elements 3.5 Isotopes and Atomic Mass

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.2 Isotopes  are atoms of the same element that have different mass numbers  have the same number of protons but different numbers of neutrons Isotopes

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.3 A nuclear symbol  represents a particular atom of an element  gives the mass number in the upper left corner and the atomic number in the lower left corner Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol: mass number atomic number Nuclear Symbol Na

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.4 For an atom, the nuclear symbol gives the number of  protons (p + )  neutrons (n)  electrons (e – ) 8 p + 15 p + 30 p + 8 n16 n35 n 8 e – 15 e – 30 e – Nuclear Symbols 16 8 O P Zn

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.5 Naturally occurring carbon consists of three isotopes, C-12, C-13, and C-14. State the number of protons, neutrons, and electrons in each of the following. protons ______ ______ ______ neutrons ______ ______ ______ electrons______ ______ ______ Learning Check 12 6 C 13 6 C 14 6 C

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.6 protons 6 p + 6 p + 6 p + neutrons 6 n7 n 8 n electrons 6 e – 6 e – 6 e – Solution 12 6 C 13 6 C 14 6 C

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.7 Write the nuclear symbols for atoms with the following subatomic particles: A. 8p +, 8n, 8e – ___________ B. 17p +, 20n, 17e – ___________ C. 47p +, 60n, 47e – ___________ Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.8 A. 8p +, 8n, 8e – B. 17p +, 20n, 17e – C. 47p +, 60n, 47e – Solution 16 8 O Cl Ag

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.9 Learning Check 1. Which of the following pairs are isotopes of the same element? 2. In which of the following pairs do both atoms have 8 neutrons? A. B. C X 15 7 X 12 6 Z 14 6 Z 15 7 Z 16 8 Z

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.10 Solution 1. B Both nuclear symbols represent isotopes of carbon with six protons each, but one has 6 neutrons and the other has C An atom of nitrogen (atomic number 7) and an atom of oxygen (atomic number 8) each have 8 neutrons.

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.11 Isotopes of Magnesium In naturally occurring magnesium, there are 3 isotopes.

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.12 Atomic Mass for Mg The atomic mass of Mg is  based on all naturally occurring Mg isotopes  not a whole number  the weighted average of the Mg-24, Mg-25, and Mg-26 isotopes

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.13 Atomic Mass The atomic mass of an element  is listed below the symbol of each element on the periodic table  gives the mass of an “average” atom of each element compared to C-12  is not the same as the mass number Na 22.99

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.14 Some Elements and Their Atomic Mass Most elements have two or more isotopes that contribute to the atomic mass of that element.

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.15 Using the periodic table, give the atomic mass of each element. A. calcium__________ B. aluminum__________ C. lead__________ D. barium__________ E. iron__________ Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.16 Using the periodic table, give the atomic mass of each element. A. calcium40.08 amu B. aluminum26.98 amu C. lead207.2 amu D. barium137.3 amu E. iron55.85 amu Solution