Chapter 4 Lecture Basic Chemistry Fourth Edition Chapter 4 Atoms and Elements 4.5 Isotopes and Atomic Mass Learning Goal Give the number of protons, electrons, and neutrons in one or more of the isotopes of an element; calculate the atomic mass of an element using the percent abundance and mass of its naturally occurring isotopes. © 2014 Pearson Education, Inc.

Isotopes are atoms of the same element that have different mass numbers have the same number of protons, but different numbers of neutrons © 2014 Pearson Education, Inc. Isotopes

© 2014 Pearson Education, Inc. An atomic symbol represents a particular isotope of an element gives the mass number in the upper left corner and the atomic number in the lower left corner mass number Atomic Symbols Chemical Symbol atomic number

© 2014 Pearson Education, Inc. Atomic Symbols, Subatomic Particles The atomic symbol indicates the number of protons, neutrons and, electrons in a specific isotope of an element. 8 protons15 protons30 protons 8 neutrons16 neutrons35 neutrons 8 electrons15 electrons30 electrons

© 2014 Pearson Education, Inc. Carbon consists of three naturally occurring isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these isotopes. Learning Check

© 2014 Pearson Education, Inc. 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 isotopes. Solution 6 protons 6 neutrons7 neutrons8 neutrons 6 electrons

© 2014 Pearson Education, Inc. 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 ____ Learning Check

© 2014 Pearson Education, Inc. 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 electron Solution

© 2014 Pearson Education, Inc. 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. Learning Check

© 2014 Pearson Education, Inc. 1. Which of the following pairs are isotopes of the same element? B. Each has 6 protons and, the element is carbon. Different mass numbers indicate that each species has a different number of neutrons. These are isotopes. Solution

© 2014 Pearson Education, Inc. Solution 2. In which of the following pairs do both atoms have 8 neutrons? C. The number of neutrons is calculated. mass number – atomic number = number neutrons 15 (mass number) – 7 (atomic number) = 8 neutrons mass number – atomic number = number neutrons 16 (mass number) – 8 (atomic number) = 8 neutrons

© 2014 Pearson Education, Inc. The atomic mass of an element is listed below the symbol of each element on the periodic table calculated based on the weighted average of all naturally occurring isotopes based on its comparison to the mass of 12 C not the same as the mass number Atomic Mass 11 Na Atomic Mass

© 2014 Pearson Education, Inc. Most elements have two or more isotopes that contribute to the atomic mass of that element. Isotopes and Atomic Mass

© 2014 Pearson Education, Inc. Magnesium has three naturally occurring isotopes. Isotopes of Magnesium

© 2014 Pearson Education, Inc. Calculating Atomic Mass The calculation for the atomic mass requires the percent(%) abundance of each isotope atomic mass of each isotope of that element To calculate atomic mass of an element with 2 isotopes: mass isotope(1) × (%)/100 + mass isotope(2) × (%)/100 Atomic mass of element

© 2014 Pearson Education, Inc. The atomic mass of Mg is a weighted average from all the Mg isotopes is not a whole number Calculating Atomic Mass

© 2014 Pearson Education, Inc. Isotope Mass Abundance 24 Mg = amu × 78.70/100 = amu 25 Mg = amu × 10.13/100 = amu 26 Mg = amu × 11.17/100 = amu Atomic mass of Mg = amu Calculating Atomic Mass 12 Mg 24.31

© 2014 Pearson Education, Inc. Using the periodic table, specify the atomic mass of each element: A. calcium__________ B. aluminum__________ C. lead__________ D. barium__________ E. iron__________ Learning Check

© 2014 Pearson Education, Inc. Using the periodic table, specify the atomic mass of each element: A. calcium amu B. aluminum amu C. lead207.2 amu D. barium137.3 amu E. iron55.85 amu Solution

© 2014 Pearson Education, Inc. The atomic mass of chlorine is the weighted average of two isotopes 35 Cl and 37 Cl. Atomic Mass Chlorine Chlorine, with two naturally occurring isotopes, has an atomic mass of

© 2014 Pearson Education, Inc. Calculating Atomic Mass of Chlorine 35 Cl has a mass of amu (75.76%), and 37 C has a mass of amu (24.24%). Use the atomic mass and percent of each isotope to calculate the weighted average amu × 75.76/100 = amu amu × 24.24/100 = amu Atomic mass of Cl amu

© 2014 Pearson Education, Inc. Learning Check Gallium is an element found in lasers used in compact disc players. In a sample of gallium, there is 60.11% of 69 Ga (68.93 amu) atoms and 39.89% of 71 Ga (70.92 amu) atoms. Given the abundance and mass of these isotopes, calculate the atomic mass of gallium.

© 2014 Pearson Education, Inc. Solution Given the abundance and mass of these isotopes, calculate the atomic mass of gallium. 69 Ga amu × 60.11/100 = amu 71 Ga70.92 amu × 39.89/100 = amu Atomic mass Ga = amu

© 2014 Pearson Education, Inc. Concept Map