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  • 1. SECTION 2.1: ATOMS FIRST <br />Review Questions <br /> 2.1Define the terms atom and element. 2.2Use a familiar macroscopic example as an analogy to describe Dalton's atomic theory. Explain why a substance such as clay or oil is not useful for an analogy of this type.<br />SECTION 2.2: SUBATOMIC PARTICLES <br />AND ATOMIC STRUCTURE <br />Review Questions <br /> 2.3Define the following terms: (a) α particle, (b) β particle, (c) γ ray, (d) X ray. 2.4Name the types of radiation known to be emitted by radioactive elements. 2.5Compare the properties of the following: α particles, cathode rays, protons, neutrons, and electrons. 2.6Describe the contributions of the following scientists to our knowledge of atomic structure: J. J. Thomson, R. A. Millikan, Ernest Rutherford, and James Chadwick. 2.7Describe the experimental basis for believing that the nucleus occupies a very small fraction of the volume of the atom.<br />Problems <br /> 2.8The diameter of an argon atom is about 2 × 102 pm. If we could line up argon atoms side by side in contact with one another, how many atoms would it take to span a distance of 1 cm? 2.9The radius of an atom is on the order of 10,000 times as large as its nucleus. If the atom were enlarged such that the radius of its nucleus were 1.0 cm, what would be the radius of the atom in meters, and in miles (1 mi = 1609 m)?<br />SECTION 2.3: ATOMIC NUMBER, MASS NUMBER, <br />AND ISOTOPES <br />Review Questions <br /> 2.10Use the argon-40 isotope to define atomic number and mass number. Why does knowledge of the atomic number enable us to deduce the number of electrons present in an atom? 2.11Why do all atoms of an element have the same atomic number, although they may have different mass numbers? 2.12What do we call atoms of the same elements with different mass numbers? 2.13Explain the meaning of each term in the symbol AZX.<br />Problems <br /> 2.14What is the mass number of an iron atom that has 31 neutrons? 2.15Calculate the number of neutrons of 243Pu. 2.16For each of the following species, determine the number of protons and the number of neutrons in the nucleus: 63Li, 2813Al, 2913Al, 5023V, 7734Se, 19377Ir. 2.17Indicate the number of protons, neutrons, and electrons in each of the following species: 178O, 2914Si, 5828Ni, 8939Y, 18073Ta, 20381Tl. 2.18Write the appropriate symbol for each of the following isotopes: (a) Z = 11, A = 23; (b) Z = 28, A = 64; (c) Z = 50, A = 115; (d) Z = 20, A = 42. 2.19Write the appropriate symbol for each of the following isotopes: (a) Z = 75, A = 187; (b) Z = 83, A = 209; (c) Z = 33, A = 75; (d) Z = 93, A = 236. 2.20Determine the mass number of (a) a beryllium atom with 5 neutrons, (b) a sodium atom with 12 neutrons, (c) a selenium atom with 44 neutrons, and (d) a gold atom with 118 neutrons. 2.21Determine the mass number of (a) a chlorine atom with 18 neutrons, (b) a phosphorus atom with 17 neutrons, (c) an antimony atom with 70 neutrons, and (d) a palladium atom with 59 neutrons. 2.22The following radioactive isotopes are used in medicine for things such as imaging organs, studying blood circulation, and treating cancer. Give the number of neutrons present in each isotope: 198Au, 47Ca, 60Co, 18F, 125I, 131I, 42K, 43K, 24Na, 32P, 85Sr, 99Tc.<br />Page 51<br />SECTION 2.4: AVERAGE ATOMIC MASS <br />Review Questions <br /> 2.23What is the mass (in amu) of a carbon-12 atom? Why is the atomic mass of carbon listed as 12.01 amu in the table on the inside front cover of this book? 2.24Explain clearly what is meant by the statement “The atomic mass of gold is 197.0 amu.” 2.25What information would you need to calculate the average atomic mass of an element?<br />Problems <br /> 2.26The atomic masses of 3517Cl (75.78 percent) and 3717Cl (24.22 percent) are 34.969 and 36.966 amu, respectively. Calculate the average atomic mass of chlorine. The percentages in parentheses denote the relative abundances. 2.27The atomic masses of 204Pb (1.4 percent), 206Pb (24.1 percent),207Pb (22.1 percent), and 208Pb (52.4 percent) are 203.973020, 205.974440, 206.975872, and 207.976627 amu, respectively. Calculate the average atomic mass of lead. The percentages in parentheses denote the relative abundances. 2.28The atomic masses of 203Tl and 205Tl are 202.972320 and 204.974401 amu, respectively. Calculate the natural abundances of these two isotopes. To seven significant figures, the average atomic mass of thallium is 204.3833 amu.2.29The atomic masses of 6Li and 7Li are 6.0151 amu and 7.0160 amu, respectively. Calculate the natural abundances of these two isotopes. The average atomic mass of Li is 6.941 amu.2.30The element rubidium has two naturally occurring isotopes. The atomic mass of 85Rb (72.17 percent abundant) is 84.911794 amu. Determine the atomic mass of 87Rb (27.83 percent abundant). The average atomic mass of Rb is 85.4678 amu. 2.31There are three naturally occurring isotopes of the element magnesium. The atomic masses of 25Mg (10.00 percent abundant) and 26Mg (11.01 percent abundant) are 24.9858374 and 25.9825937 amu, respectively. What is the atomic mass of 24Mg (78.99 percent abundant) given the average atomic mass of Mg is 24.3050 amu?<br />SECTION 2.5: THE PERIODIC TABLE <br />Review Questions <br /> 2.32What is the periodic table, and what is its significance in the study of chemistry? 2.33Write the names and symbols for four elements in each of the following categories: (a) nonmetal, (b) metal, (c) metalloid. 2.34Give two examples of each of the following: (a) alkali metals, (b) alkaline earth metals, (c) halogens, (d) noble gases, (e) chalcogens, (f) transition metals. 2.35The explosion of an atomic bomb in the atmosphere releases many radioactive isotopes into the environment. One of the isotopes is 90Sr. Via a relatively short food chain, it can enter the human body. Considering the position of strontium in the periodic table, explain why it is particularly harmful to humans.<br />Problems <br /> 2.36Elements whose names end with -ium are usually metals; sodium is one example. Identify a nonmetal whose name also ends with -ium. 2.37Describe the changes in properties (from metals to nonmetals or from nonmetals to metals) as we move (a) down a periodic group and (b) across the periodic table from left to right. 2.38Consult the WebElements Periodic Table of the Elements ( to find (a) two metals less dense than water, (b) two metals more dense than mercury, (c) the densest known solid metallic element, and (d) the densest known solid nonmetallic element. 2.39Group the following elements in pairs that you would expect to show similar properties: K, F, P, Na, Cl, and N. 2.40Group the following elements in pairs that you would expect to show similar chemical properties: I, Ba, O, Br, S, and Ca. 2.41Write the symbol for each of the following biologically important elements in the given periodic table: iron (present in hemoglobin for transporting oxygen), iodine (present in the thyroid gland), sodium (present in intracellular and extracellular fluids), phosphorus (present in bones and teeth), sulfur (present in proteins), and magnesium (present in chlorophyll).<br />SECTION 2.6: THE MOLE AND MOLAR MASS <br />Review Questions <br /> 2.42Define the term mole. What is the unit for mole in calculations? What does the mole have in common with the dozen and the gross? What does Avogadro's number represent? 2.43What is the molar mass of an element? What units are commonly used for molar mass?<br />Problems <br /> 2.44Earth's population is about 6.8 billion. Suppose that every person on Earth participates in a process of counting identical particles at the rate of two particles per second. How many years would it take to count 6.0 × 1023 particles? Assume that there are 365 days in a year. 2.45The diameter of a human hair is 25.4 μm. If atoms with a diameter of 121 pm were aligned side by side across the hair, how many atoms would be required?Page 52 2.46How many atoms are there in 1.60 moles of selenium (Se)? 2.47How many moles of nickel (Ni) atoms are there in 5.00 × 109 (5 billion) Ni atoms? 2.48How many moles of strontium (Sr) atoms are in 93.7 g of Sr? 2.49How many grams of platinum (Pt) are there in 26.4 moles of Pt? 2.50What is the mass in grams of a single atom of each of the following elements: (a) Os, (b) Kr? 2.51What is the mass in grams of a single atom of each of the following elements: (a) Sb, (b) Pd? 2.52What is the mass in grams of 2.00 × 1012 tin (Sn) atoms? 2.53How many atoms are present in 4.09 g of scandium (Sc)? 2.54Which of the following has more atoms: 4.56 g of helium atoms or 2.36 g of manganese atoms? 2.55Which of the following has a greater mass: 173 atoms of gold or 7.5 × 10−22 mole of silver?<br />ADDITIONAL PROBLEMS <br /> 2.56A sample of uranium is found to be losing mass gradually. Explain what is happening to the sample. 2.57The element francium (Fr) was the last element of the periodic table discovered in nature. Because of its high radioactivity, it is estimated that no more than 30 g of francium exists at any given time throughout the Earth's crust. Assuming a molar mass of 223 g/mol for francium, what is the approximate number of francium atoms in the Earth's crust? 2.58One isotope of a metallic element has 35 neutrons in the nucleus. The neutral atom has 30 electrons. Write the symbol for this atom. 2.59An isotope of a nonmetallic element has mass number 131. An atom of this isotope contains 54 electrons. Write the symbol for this atom. 2.60Using the information provided in the table, write a symbol for each atom. If there is not enough information, state what additional information is needed to write a correct symbol for that atom. Atom of element ABCDNumber of electrons61129 Number of protons6 2936Number of neutrons67 47 2.61Using the information provided in the table, write a symbol for each atom. If there is not enough information, state what additional information is needed to write a correct symbol for that atom. Atom of element ABCDNumber of electrons10 2150Number of protons 752150Number of neutrons1211021  2.62Which of the following symbols provides more information about the atom: 23Na or 11Na? Explain. 2.63Discuss the significance of assigning an atomic mass of exactly 12 amu to the carbon-12 isotope. 2.64List the elements that exist as gases at room temperature. (Hint: Most of these elements can be found in Groups 5A, 6A, 7A, and 8A.) 2.65For the noble gases (the Group 8A elements) 42He, 2010Ne, 4018Ar, 8436Kr, 13254Xe (a) determine the number of protons and neutrons in the nucleus of each atom, and (b) determine the ratio of neutrons to protons in the nucleus of each atom. Describe any general trend you discover in the way this ratio changes with increasing atomic number. 2.66The carat is the unit of mass used by jewelers. One carat is exactly 200 mg. How many carbon atoms are present in a 2.5-carat diamond?2.67In the geologic record of Earth, the disappearance of the dinosaurs roughly 65 million years ago is marked by a thin line known as the K-T boundary. Because the K-T boundary contains an unusually high concentration of the element iridium, which is ordinarily quite rare in Earth's crust, geologists have deduced that the mass extinction was caused by the catastrophic impact of an asteroid. The two naturally occurring isotopes of iridium are 191Ir and 193Ir, with atomic masses of 190.960584 and 192.962917 amu, respectively; and abundances of 37.3 percent and 62.7 percent, respectively. Determine the average atomic mass of iridium and compare your result with the atomic mass given in the periodic table. 2.68One atom of a particular element with only one naturally occurring isotope has a mass of 3.002 × 10−22 g. What element is this? 2.69Identify each of the following elements: (a) a halogen containing 53 electrons, (b) a radioactive noble gas with 86 protons, (c) a Group 6A element with 34 electrons, (d) an alkali metal that contains 11 electrons, (e) a Group 4A element that contains 82 electrons. 2.70Show the locations of (a) alkali metals, (b) alkaline earth metals, (c) the halogens, and (d) the noble gases in the given outline of a periodic table. Also draw dividing lines between metals and metalloids and between metalloids and nonmetals.Page 53 2.71While most isotopes of light elements such as oxygen and phosphorus contain relatively equal amounts of protons and neutrons in the nucleus, recent results indicate that a new class of isotopes called neutron-rich isotopes can be prepared. These neutron-rich isotopes push the limits of nuclear stability as the large numbers of neutrons approach the “neutron drip line.” Neutron-rich isotopes may play a critical role in the nuclear processes of stars. Determine the number of neutrons in the following neutron-rich isotopes: (a) 40Mg, (b) 44Si, (c) 48Ca, (d) 43Al. 2.72Fill in the blanks in the table: Symbol   Protons 14  Neutrons15  117Electrons  79 2.73Fill in the blanks in the table: Symbol  Protons   62Neutrons  108 88Electrons 73  2.74(a) Describe Rutherford's experiment and how the results revealed the nuclear structure of the atom. (b) Consider the 23Na atom. Given that the radius and mass of the nucleus are 3.04 × 10−15 m and 3.82 × 10−23 g, respectively, calculate the density of the nucleus in g/cm3. The radius of a 23Na atom is 186 pm. Calculate the density of the space occupied by the electrons outside the nucleus in the sodium atom. Do your results support Rutherford's model of an atom? (The volume of a sphere of radius r is .) 2.75A cube made of platinum (Pt) has an edge length of 1.0 cm. (a) Calculate the number of Pt atoms in the cube. (b) Atoms are spherical in shape. Therefore, the Pt atoms in the cube cannot fill all the available space. If only 74 percent of the space inside the cube is taken up by Pt atoms, calculate the radius in picometers of a Pt atom. The density of Pt is 21.45 g/cm3, and the mass of a single Pt atom is 3.240 × 10−22 g. (The volume of a sphere of radius r is .) 2.76In the facing page of the periodic table at the front of this book is an alphabetical list of elements with atomic masses given to the number of known significant figures. Compare the number of significant figures given for aluminum, bismuth, lead, and molybdenum. Look these elements up on and explain why their atomic masses are reported to such different numbers of significant figures.<br />