Chemistry 20 Name: _____________ Unit II: Atoms and Elements 4.3 How Atoms Differ I. Skim pages 98 - 104 of the textbook. After reading the headlines and looking at the pictures predict 3 things that you think that you will be reading about in this section. 1. _______________________________________________________ 2. _______________________________________________________ 3. _______________________________________________________ II. The learning objectives for this section are: 1. Define and give an example of: atomic number, isotope, mass number, atomic mass unit (amu), and atomic mass. 2. Explain the role of atomic number in determining the identity of an atom. 3. Explain why atomic mass are not whole numbers. 4. Calculate the number of electrons, protons, and neutrons in an atom given its mass number and atomic number. 5. Calculate atomic mass values when given the percentage of each isotope of an element. III. The following questions will help to cover these objectives as you read through the section. 1. What identifies an atom as belonging to a particular element? 2. What can be determined by knowing an element’s atomic number? 3. Read over the example problem on page 99 and work through practice problems 11 – 13 on the same page (use the back of the book for to check your answers. Complete the following: a) How many protons and electrons are contained in an atom of element 44? b) For each of the following chemical symbols, determine the element name and the number of protons and electrons an atom contains. Chemical symbol V Ir Mn S 4. Element name # of protons # of electrons Why was Dalton’s Atomic Theory point about all atoms of a particular element are identical slightly incorrect? 5. How do isotopes differ from each other in a particular element? 6. Explain why isotopes of a particular element still have the same chemical behaviours? 7. How are the number of neutrons, the mass number, and the atomic number of a particular element all related to one another? 8. Draw and explain the notation you see in Figure 4-15 on page 100. 9. Read over the example problem on page 101 and work through practice problem 14 on the same page (use the back of the book for to check your answers. Complete the following: a) A carbon atom has a mass number of 12 and an atomic number of 6. How many neutrons does it have? b) An isotope of mercury has 80 protons and 120 neutrons. What is the mass number of this isotope? c) An isotope of xenon has an atomic number of 54 and contains 77 neutrons. What is the xenon isotope’s mass number? d) Complete the following table. The number after the element name refers to the atomic mass. Isotope 132 55Cs 59 27Co 163 69Tm 70 30Zn gallium-64 fluorine-23 titanium-48 helium-8 10. # of electrons # of protons # of neutrons Why are atomic masses not whole numbers on the periodic table? 11. Read over the example problem on page 103-104 and work through practice problems 15-17 on the same page (use the back of the book for to check your answers. Complete the following: a) In your own words list the steps in the process of calculating average atomic mass given data about the isotopes of an element. b) Chlorine, which has an atomic mass of 35.453 amu, has two naturally isotopes, Cl-35 and Cl-37. Which isotope occurs in greater abundance? Explain. c) Silver has two isotopes, 109 47Ag silver? 107 47Ag has a mass of 106.905 amu (52.00%), and has a mass of 108.905 amu (48.00%). What is the atomic mass of d) Data for chromium’s four naturally occurring isotopes is provided in the table below. Calculate chromium’s atomic mass. Isotope Cr-50 Cr-52 Cr-53 Cr-54 Percent abundance 4.35% 83.79% 9.50% 2.36% Mass (amu) 49.946 51.941 52.941 53.939