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Name Date Properties of Atoms and the Periodic Table Section 2 Masses of Atoms Preview Section 2 of your book, using the checklist below. • Read all section titles. • Read all boldfaced words. • Read all charts and graphs. • Look at all the pictures and read their captions. • Think about what you already know about masses of atoms. Write three facts you learned. 1. Accept all reasonable answers. Protons identify an element. 2. Radioactive isotopes are used to measure the age of fossils. 3. An electron’s mass is negligible. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Review Vocabulary Define mass to show its scientific meaning. mass amount of matter in an object New Vocabulary Use your book or dictionary to define the following key terms. atomic number mass number isotope average atomic mass a number equal to the number of protons in an atom’s nucleus sum of the number of protons and neutrons in an atom atoms of the same element with different numbers of neutrons the average mass of the mixture of isotopes of an element Academic Vocabulary Use a dictionary to find the scientific meaning of define. define to determine or identify the essential qualities or meaning of something Properties of Atoms and the Periodic Table 195 Name Date Section 2 Masses of Atoms Atomic Mass I found this information on page . SE, pp. 494–495 RE, p. 284 (continued) Organize the information on atomic mass to complete the outline. Atomic Mass A. Nucleus of atom 1. contains most of the mass of an atom 2. masses of protons and neutrons in a nucleus are nearly identical 3. electron’s mass is so small it is not included in atomic mass B. Atomic mass unit 1. amu appropriate unit for measuring the size of a particle 2. equals one-twelfth the mass of a carbon atom C. Protons 1. number of protons is used to identify elements 2. each element has different number of protons 3. number of electrons equals the number of protons in an element 4. number of protons equals the atomic number of the element D. Mass number 1. equals the sum of the number of protons plus neutrons of an atom 2. atoms of the same element can have different number of neutrons and a different mass number 196 Properties of Atoms and the Periodic Table Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 3. each proton and each neutron has a mass of about 1 amu Name Date Section 2 Masses of Atoms Isotopes I found this information on page . SE, pp. 496–497 RE, p. 286 (continued) Model carbon-12 and carbon-14 by sketching each atom. • Remember that carbon’s atomic number is 6. • Label each atom’s protons, neutrons, and electrons. • Show the charges of the particles. Student drawings should resemble figure on SE p. 515 or RE p. 291, but with 6 protons, and 6 neutrons. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Carbon-12 Student drawings should resemble figure on SE p. 515 or RE p. 291, but with 6 protons, and 8 neutrons. Carbon-14 Analyze how you would determine which isotope of an element is the most abundant if you know the element’s average atomic mass. Accept all reasonable answers. Round the average atomic mass to the nearest whole number to find the most abundant isotope. CONNECT IT While exploring on your grandfather’s farm, you come across what appears to be ancient Native American artifacts, arrowheads, and tools. Explain how you could find out the age of these pieces and if they are, in fact, an archeological find. Accept all reasonable answers. Student answers should describe the use of carbon-14, explanation of half-life, and radioactivity to identify organic parts of the artifacts. Properties of Atoms and the Periodic Table 197