U N I 1. laboratory tools and chemistry techniques.
UNIT 1 Lesson 1 Exercises 1. Possible answer: Chemistry containers are made of glass because substances in a glass container are visible and glass containers are relatively easy to clean and reuse. Tempered glass containers can be heated over flames without shattering. 2. Possible answer: Appropriate clothing provides protection, and has no loose or dangling parts to interfere with safe lab procedures. While in the lab, tie back long hair and wear safety goggles, long pants or skirts, and shoes with closed toes. Remove any dangling jewelry. 3. Possible answers (any 3): • Know the location of safety equipment. • Read lab instructions carefully. • Check to be sure that you are using the right chemicals and equipment. • Follow directions from the teacher. • Discuss the steps of the procedure with other members of the group and assign tasks. 4. Possible answer: Immediately report the spill to the teacher and follow instructions for cleaning it up. If you come into contact with any chemicals, rinse the affected area with water for at least 15 minutes. 5. Possible answers (any 3): • Put all equipment in its proper place. • Clean your work area. • Make sure all bottles and containers holding chemicals are closed and stored properly. • Safely dispose of used chemicals as indicated by the teacher. • Wash your hands. 6. A fire blanket is used to extinguish flames by smothering a fire and depriving it of oxygen. 7. A hood keeps gases and fumes from entering the laboratory by carrying them to a filter or by venting them to the outdoors. 8. Chemists use clamps and ring stands to keep glassware from toppling over and breaking or spilling. Living By Chemistry Solutions Manual Lesson 2 Exercises 1. Alchemists developed some of the first laboratory tools and chemistry techniques. They classified substances into categories and experimented with mixing and heating different substances to create something new. 2. Chemistry is the study of what substances are made of, how they behave, and how they can be transformed. It is the study of matter and how matter changes. 3. Time periods when alchemy was practiced: China (early c.e.), India (b.c.e. to Middle Ages), Middle East (early c.e. to recent), Greece (late b.c.e. to early c.e.), Spain (Middle Ages), England (Middle Ages), Egypt (b.c.e.). A good answer will include • goals of alchemists in their particular region (which substances they were attempting to transform or obtain) • contributions that alchemists in the region made to science • a list of trustworthy sources for the information given in the answer 4. Possible answer: Sodium hydroxide, or lye, is a strong base used in manufacturing paper, soaps and detergents, and in other industrial chemical processes. In the home, sodium hydroxide is a component of many drain cleaners. Because it is a strong base, and therefore a very reactive substance, sodium hydroxide is an important industrial chemical used in many chemical manufacturing processes. It tends to break down organic materials, such as hair and grease, which makes it useful as a drain cleaner. 5. Possible answer (any 10 examples total): • Changes that involve chemistry involve an alteration in the appearance of matter. Examples include metal rusting, cookies baking, ice cubes forming, wood burning, water boiling, and sugar dissolving. Both physical changes (such as changes of state) and chemical changes (such as objects burning or rusting) involve chemistry. • Changes that do not involve chemistry only involve matter moving to a different location. Examples include the sun going down, objects falling, hands moving on a clock, going for a walk, throwing a ball, and riding a bicycle. Unit 1 Alchemy 1 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 1 4/16/12 3:32:00 PM Lesson 3 Exercises 1. Mass is the amount of material in an object. Volume is the amount of space that the object takes up. 2. Possible answer: A bicycle has mass because when you lift it you can feel its weight. You could further prove this by placing the bicycle on a scale. A bicycle has volume because you can see that it fills space that cannot be occupied by anything else. You could further prove this by lowering a bicycle into a bathtub and watching the water level rise. Since it has mass and volume, the bicycle is matter. 2. Possible answer: Not necessarily. Two objects with the same volume can have very different masses. For example, a cube of iron has much more mass than a cube of wood that has the same volume. 3. Yes, the volume of an object is the amount of space it fills. You can usually see how much space an object fills, and estimate its volume based on its dimensions. However, for objects that have an irregular shape, are very thin, or have a surface with lots of holes or pits, determining the volume of the object by sight may be difficult. 3. Possible answer: If you use a balance to find the mass of an empty balloon, then inflate the balloon with air and tie off its end, you will see that its mass has increased when you put it back on the balance. The air inside the balloon must have mass. Because the volume of the balloon increases when the balloon is inflated with air, the air inside the balloon also has volume. Since the air inside the balloon has mass and volume, it is matter. 4. No, the mass of an object does not depend only on its shape and size, so you cannot predict an object’s mass simply by looking at the object. An incorrect answer is that the mass of a known object, such as a piece of metal, can be predicted by looking at its size. In this case, knowledge about density is being used in addition to visual information, or the assumption is made that an object is made of a certain material just by looking. 4. Possible answer: The Sun is matter because it has mass and volume. Sunlight is not matter because it does not have mass or volume. It is a form of energy that can be detected visually and that makes your skin feel warm. 5. Yes, the mass of the rubber band is the same because only the shape of the rubber band changes, not the amount of matter in it. 5. Possible answer (any 10 of each): • Examples of things that are matter: a car, a tree, a person, a cat, a brick, a desk, a pen, water, a glass, a window, a rock, and the Sun. Each of these objects has mass and volume. • Examples of things that are not matter: light, sound, movement, gravity, music, heat, time, cell phone signals, feelings, energy, radio waves, thoughts, memories, and forces. These things do not have mass or volume. They are forms of energy or are intangible. 6. Possible answers (any 5): sound, wind, rolling, falling, running, flying, explosion, rain Lesson 4 Exercises 1. Possible answer: To determine the measure of a solid object, measure its dimensions and calculate the volume using a geometric formula or, if it does not float or dissolve, measure the amount of liquid that it displaces when it is submerged. 2 Unit 1 Alchemy LBC1eSM_01.indd 2 6. a. Volume is the measure of the amount of space the piece of clay occupies. Changing its shape does not change the amount of space it occupies. b. No, the mass of the clay does not change, because you did not add or subtract any matter from the clay, and mass is a measure of the amount of matter. 7. Possible answers: a. Pour the pancake mix into a graduated cylinder or a measuring cup and read the markings. b. Use a measuring spoon or measuring cup. c. Measure the dimensions of the box and multiply the length by the width by the height. d. Measure the thickness and radius of the penny and calculate its volume using the formula for the volume of a cylinder or measure the amount of liquid it displaces when it is submerged. e. Pour the lemonade into a graduated cylinder or a measuring cup and read the markings. Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:00 PM The key concept of the question is that the volume of fluids can be measured directly, while the volume of a solid material can be best measured by its dimensions or displacement. 8. Possible answer: The exercise specifies that the cubes are exactly the same material, so they should have the same mass since they are the same volume. This eliminates the possibility that the substance is wood, plastic, or some other substance where the density may vary. The only remaining possibility is measurement error due to human error or limits to the instrument’s precision. Lesson 5 Exercises 1. Possible answer: Density is the mass of an object divided by its volume. The drawing should clearly show that the masses of the two objects are the same. This can be done using a balance, as shown above, or by using labels. For example, a large cube could be labeled “polystyrene foam” and a small cube labeled “wood.” 9. Possible answer: 2. If the density of the penny (its mass divided by its volume) is not equal to the density of gold (19.3 g/cm3), then the penny is not made of solid gold. 3. The density of aluminum is less than the density of gold. More matter is present in a given volume of gold than in the same volume of aluminum. 4. C The drawing should clearly show that the masses of the two objects are different. This can be done using a balance, as shown above, or by using labels. For example, two beakers could be shown, one labeled “sand” and the second labeled “water.” 10. a. 150 mL b. Because the rock is completely submerged in the water, the volume of the rock is equal to the volume of water that it displaces. The displaced volume is equal to the change in the water level: 200 mL − 150 mL = 50 mL. One mL is equal to one cm3 , so the volume of the rock is 50 mL, or 50 cm3. 11.Possible answer: The balance or scale that was used to measure the two different cubes may not be able to measure accurately to a hundredth of a gram. The two cubes could have exactly the same mass because the measurement error is greater than 0.03 g. Living By Chemistry Solutions Manual 5. Possible answer: The object that has a density of 2.7 g/cm3 has a larger volume than the object with a density of 8.4 g/cm3. The two objects have the same mass, but the mass is packed into a smaller space in the denser object. m 6. D __ V 252 g ________ 30.0 cm3 8.40 g/cm3 The metal could be brass because the table shows that the density of brass is 8.4 g/cm3. Brass is a possible identification based on the table but note that density alone is not adequate to identify a material because other materials could have the same density. m 7. a. D __ V 18.5 g ________ 6.45 cm 3 2.87 g/cm3 b. 6 • 18.5 g 111 g 6 • 6.45 cm3 38.7 cm3 Unit 1 Alchemy 3 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 3 4/16/12 3:32:00 PM m D __ V 111 g ________ 38.7 cm 3 2.87 g/cm3 c. The density of six glass marbles is the same as the density of one glass marble because density is an intensive property of the glass in the marbles. Section I Review Questions 1. Possible answer: Determine the volume of a powdered solid or of a liquid by pouring the substance into a graduated cylinder or beaker and reading the markings on the side. Determine the volume of a rock by submerging the rock in a graduated cylinder partially filled with water and then reading how much the water level changes. 2. Possible answer: Matter is anything that has mass and takes up space. 3. Density is no help in determining which object will displace more water. A large object will displace more water than a small object no matter how dense the two objects are. m 4. D __ V 2.6 g D(one penny) ________ 0.36 cm3 7.2 g/cm3 5.2 g D(two pennies) ________ 0.72 cm3 7.2 g/cm3 The density of one penny is the same as the density of two pennies. 5.Possible answer: The density is the same because the pebble is made of the same material as the boulder. Although the pebble has a smaller mass, it also has a smaller volume, so the density can be the same. 6. m DV 10.5 g/cm3 • 238.1 cm3 Lesson 6 Exercises 1. Elements are the building materials of all matter. A compound is matter that is made up of two or more elements combined in a specific ratio. An element cannot be broken down into simpler substances by chemical means, but a compound can be broken down into elements. 2. The physical form of a substance is its phase: gas, liquid, or solid. An aqueous solution is another physical form. 3. The chemical formula for sodium nitrate, NaNO3, indicates that it has three elements: sodium, Na, nitrogen, N, and oxygen, O. 4. NaOH(s) is the symbol for solid sodium hydroxide. NaOH(aq) indicates that the sodium hydroxide is dissolved in water. 5. The chemical formula for cubic zirconia is ZiO2. The chemical formula for diamond is C. The stone cannot be a diamond because it has a different chemical formula than a diamond. 6. These steps present possible dangers: • Step 2: Wear goggles and gloves to protect your eyes and skin from the nitric acid. Do your work under the hood to avoid breathing harmful gases. Pour the liquid slowly to avoid spills. In case of skin contact, wash your skin and notify the teacher. • Step 3: Wear goggles and gloves to protect your eyes and skin from the sodium hydroxide. Pour the liquid slowly to avoid spills. In case of skin contact, wash your skin and notify the teacher. • Step 4: Avoid touching the beaker or the hot plate directly. Wear gloves to protect your skin. Stir the liquid carefully to avoid splashing hot liquid. In case of skin contact, wash your skin and notify the teacher. • S tep 5: Avoid touching the beaker or the hot plate. Wear gloves to protect your skin. Be careful transporting the beaker to the lab table. In case of skin contact, or a dropped beaker, notify the teacher, wash your skin, and make sure to sweep up all the pieces of broken glass. 2500 g 4 Unit 1 Alchemy LBC1eSM_01.indd 4 Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:01 PM • Step 8: Wear goggles and gloves to protect your eyes and skin from the sulfuric acid. Pour the liquid slowly and stir carefully to avoid spills. In case of skin contact, wash your skin and notify the teacher. Lesson 7 Exercises 1. Possible answer: A chemical reaction is a change leading to the final substance or substances being different from the original substance or substances. Some of the signs that a new substance has formed include • color changes • formation of a new solid • formation of a gas • the release of energy as heat or light • an increase or decrease in the mass of material • a change in the texture of a material 2. Possible answer: The copper would always be present throughout the series of reactions. The copper could be in a different form after each reaction. For example, the copper could become part of a compound, then be dissolved in water, and then extracted and returned to its pure form. 3. Possible answer: A chemical reaction combined the zinc with part of the dissolved copper compound. The resulting zinc compound was also dissolved in water. The zinc was still present, but not as a pure element. In fact, when the zinc was added, it formed a colorless solution of zinc sulfate and the copper came out of the solution as a precipitate. 4. Yes, the ingredients undergo a chemical change. The cookies are a different color and consistency from the cookie dough. These changes are present even after the cookies cool to room temperature. As the cookies bake, the dough absorbs heat energy, which causes a chemical change in the ingredients of the dough. The composition of the cookies is very different from the original ingredients and from the dough. Living By Chemistry Solutions Manual 5. a. The baking soda is a solid, the vinegar is a liquid, the clear colorless liquid is a liquid, and the CO2is a gas. b. Yes, the production of carbon dioxide gas is evidence that a chemical change has occurred after the original liquid and solid substances were mixed. The solution also becomes colder and the odor of the vinegar disappears—other indications of the chemical change. c. Before the change, the sodium is in the solid baking soda. After the change, the sodium must be in the clear colorless liquid. In fact, when baking soda is mixed with vinegar, the result is sodium acetate, CH3COONa, dissolved in water. 6. Possible answer: Copper ore is crushed into a powder and changed to a copper sulfate solution by a chemical reaction. When an electric current passes through the solution, the copper metal comes out of the solution as copper deposited on a metal plate. Lesson 8 Exercises 1. Possible answer: The chemical names and symbols indicate what compounds were combined in each step. Because matter is conserved, the products must contain the same elements as the original compounds, which enables you to make a reasonable guess about the products. For example, when sulfuric acid combines with copper oxide, it is likely that copper sulfate and water are the products. 2. Possible answer: The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. 3. A good lab report will contain • a title (Lab: The Copper Cycle) • a statement of purpose (Possible Answer: To perform a series of chemical reactions that begin and end with copper powder) • a procedure (a summary of the steps followed in the experiment) • results (Check student observations to make sure they noticed the changes that occurred during each step of the copper cycle, including color changes, formation of gas, formation of precipitates, and dissolving of solid materials.) Unit 1 Alchemy 5 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 5 4/16/12 3:32:01 PM • a conclusion (The conclusion should include a statement related to the conservation of matter. Possible answer: Although the copper seemed to disappear, it was still present in the substances in the beaker during the entire series of chemical reactions. This was proved by recovering the copper at the end of the series of reactions.) 4. Possible answer: The copper cycle experiment shows that the copper is never lost and implies that it is a component in other compounds formed during the experiment. Elements also cannot be broken down into more fundamental building blocks. The copper cycle experiment does not prove that copper cannot be broken down into simpler building blocks. But, the experiment does support the conclusion that copper is an element based upon the definition of element given in Lesson 6. 5. The solution would be yellow because the combination of nickel, Ni, and hydrochloric acid, HCl, can only produce a solution containing compounds with nickel, hydrogen, and chlorine. Nickel chloride, NiCl2, is a possible product and forms a yellow solution. Nickel sulfate, NiSO4, is not a possible product. 6. The zinc reacts with the sulfate part of the copper sulfate to form an aqueous solution of zinc sulfate. The precipitate is pure copper, so the zinc and the sulfate must be present in the dissolved compound. 7. Possible answers (any 2): • Oxygen, carbon dioxide, water, and other important resources can cycle through the environment over and over again. • Dangerous waste products that cannot break down into safer substances will always be present in the environment. • The resources that are currently available on the planet are the only resources that will ever be available, unless a method of bringing more material from outer space to Earth is developed. Lesson 9 Exercises 1. Three useful properties for sorting elements are reactivity, formulas of their compounds, and atomic mass. 6 Unit 1 Alchemy LBC1eSM_01.indd 6 2. Carbon, C, is most similar to silicon, Si, because both elements are located in the same column of Mendeleyev’s periodic table of the elements. Mendeleyev sorted the elements, placing elements with similar properties in the same column. Carbon is in the same column as silicon, but not in the same column as nitrogen and oxygen. 3. a. Possible answer: Si P Ge S Se Sn Sb b. Possible answers (any 2 for each column): • Column 1: Combines with chlorine in a 1:4 ratio, solid at room temperature, nonreactive. • Column 2: Combines with chlorine in a 1:3 or a 1:5 ratio, reactive, brittle, solid at room temperature. • Column 3: Combines with chlorine in a 1:2 ratio, reactive, brittle, solid at room temperature. Multiple correct answers are possible. The answer above uses the same logic as was followed in Lesson 9. The columns are organized using the ratios of the atoms when combined with chlorine. The rows are organized using the atomic mass of the elements. • silicon: average atomic mass 28.09, gray, solid, metalloid, nonreactive, forms compound SiCl4 • germanium: average atomic mass 72.61, gray, solid, metalloid, nonreactive, forms compound GeCl4 • tin: average atomic mass 118.7, silverywhite, solid, metal, nonreactive, forms compound SnCl4 • phosphorus: average atomic mass 30.97, white or red, solid, nonmetal, brittle, reactive, forms compounds PCl3 and PCl5 • antimony: average atomic mass 121.8, silverywhite, solid, metalloid, brittle, reactive, forms compounds SbCl3 and SbCl5 • sulfur: average atomic mass 32.07, yellow, solid, nonmetal, brittle, reactive, forms compound SCl2 Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:01 PM • selenium: average atomic mass 78.96, gray or red, solid, nonmetal, brittle, reactive, forms compound SeCl2 4. Possible answer: Nails are made of iron because iron is hard and fairly stable in air and water. Barium is too soft for a nail and it reacts easily with water. Phosphorus is a brittle solid that is difficult to shape and would break when struck by a hammer. Phosphorus also reacts too easily with air and water. • iron: hard, heavy gray metal; reacts slowly with water and oxygen • barium: soft, silvery metal that reacts easily with water and oxygen • phosphorus: soft, white or red crystalline solid, brittle, very reactive with water and oxygen 5. a. CaS b. The compound with sulfur will have more mass for a given amount of calcium. The two compounds have the same number of atoms, but the atomic mass of sulfur is 32, and the atomic mass of oxygen is only 16. 6. Possible answer: Dmitri Mendeleyev was the youngest child in a large family. He and his mother moved to St. Petersburg, Russia, when his father died. After finishing school he began teaching science while studying chemistry. He became a professor of chemistry and wrote a textbook called Principles in Chemistry. While working on the book, he noticed patterns in the properties of the elements. He made cards with the symbols and properties of the elements and began to arrange them. Based on the patterns he saw in the card arrangements, Mendeleyev developed his periodic table. 7. Possible answers: a. Both versions arrange the elements in the same order with the same atomic numbers. The columns and rows include the same elements in both versions. Elements are arranged in order of increasing atomic mass. b. The specific information about each element, such as average atomic mass, differs between the tables. The names and symbols of elements 110 and higher are different.The placement of the lanthanides and actinides differs between the tables. Living By Chemistry Solutions Manual Lesson 10 Exercises 1. Within Group 1A, the elements tend to get more reactive as you move from the top of the column to the bottom. Metallic characteristics tend to increase as you move from the top of the table to the bottom. The most reactive metals are located in the lower left portion of the periodic table. 2. Possible answers (any 2): • Reactivity of elements within a period decreases from the left edge to the center and then increases from the center to the right side. However, the element at the far right side of the period is very nonreactive. • Elements change from metal to metalloid and finally to nonmetal as you move left to right. • Average atomic mass increases as you move left to right. • Phase changes from solid on the left to gas on the far right. • Heat conductivity decreases as you move left to right. • Conductivity decreases as you move left to right. 3. a. Label groups as follows • alkali metals: first column on left, excluding hydrogen • alkaline earth metals: second column from left • halogens: second column from right • noble gases: last column on right b. Label sections of table as follows • main group elements: first two columns on left and last six columns on right (Groups 1A–8A) • transition elements: the elements in the B groups between the main group elements • lanthanides: elements 57 through 70 • actinides: elements 89 through 102 4. Only two elements in Group 2A have average atomic masses greater than 130—barium and radium. 5. B, C, E, and F 6. A B, and E Unit 1 Alchemy 7 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 7 4/16/12 3:32:01 PM 7. Copper and mercury are the least reactive. On the periodic table the least reactive elements (aside from the noble gases) are the transition metals that are located in the center of the table. The other elements listed are from more reactive groups near the edge of the table: alkali metals (potassium and rubidium), alkaline earth metals (barium), and halogens (chlorine). 8. Possible answer: Copper and platinum, as transition metals, are not very reactive and therefore can be used to make jewelry. Sodium, an alkali metal, is very reactive and not suitable for making jewelry. Neon, a gas, cannot be used to make jewelry. Section II Review Questions 1. Possible answer: Gold, represented by the symbol Au, is a transition metal that is a solid at room temperature. It has an atomic number equal to 79 and an average atomic mass of 197.0. Gold is nonreactive, a good conductor of heat, and a good conductor of electricity. It has similar properties to copper and silver. 2. Possible answer: During a chemical reaction matter changes from one form to another, but the total amount of each element in the matter does not change. The products of a reaction, such as the reactions in the Lab: The Copper Cycle, can often be predicted based on the materials that react. 3. Possible answer: A chemical formula is a symbol that represents a compound. The chemical formula shows what elements are in the compound and the ratio in which the elements combined. It can also show what physical form the compound is in. 4. Possible answer: Tungsten might be useful for a light bulb filament because it is a solid metal. Bromine is unsuitable because it is a liquid. Sulfur is unsuitable because it is not a metal and therefore is a poor conductor and is not malleable. Also, elements toward the left of the periodic table are better conductors of electricity than sulfur. Project: Element Profile A good report would include • a definition and explanation of the law of conservation of mass 8 Unit 1 Alchemy LBC1eSM_01.indd 8 • a general description of the element and its properties • a list of all the common uses of an element • a description of how abundant the element is and how it is mined or extracted • a description of the role the element plays in the environment, or the environmental impact of the element’s extraction and use in industry • an analysis of how the element’s uses and environmental roles relates to the law of conservation of mass • future projections of the availability and uses of the element Lesson 11 Exercises 1. When Thomson zapped atoms with electricity, he found that a negatively charged particle was removed. Because the solid sphere model does not allow for particles splitting off atoms, he created the plum pudding model. If negatively charged parts of the atom can be removed, then a separate part of the atom must be positively charged. Thomson reasoned that an atom consists of a positively charged fluid that contains negatively charged particles called electrons. 2. When Rutherford shot alpha particles at a thin layer of atoms, most of them went straight through, but some bounced back. The plum pudding model does not have any solid parts, nor does it have any concentrations of positive charge that would repel the alpha particles. So, Rutherford created the nuclear model. Some of the positive particles were deflected but most passed through. Rutherford reasoned that the positively charged part of the atom must make up a very small part of the total volume. He called this concentration of positive charge the nucleus and reasoned that the electrons orbited within the vast empty space surrounding the nucleus. 3. Bohr revised the nuclear model of the atom when he noticed different atoms giving off different colors of light when exposed to flame or electric fields. Because the nuclear model fails to account for this process, he created the solar system model. Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:01 PM Bohr suggested a model in which the electrons orbit around the nucleus at different distances, and proposed that these electrons have different energies. Bohr reasoned that the different levels of light energy emitted correspond to different changes in energy that occur when electrons move from an outer orbit to an inner orbit. 4. Both a proton and a nucleus are attracted to a negative charge because they have a positive charge. Because an electron has a negative charge, it will be repelled by a negative charge. Because neither a neutron nor an atom have a charge, they will be neither attracted nor repelled by a negative charge. 5. Possible answer: The two types of atoms could have different amounts of positive fluid and different numbers of electrons, as shown in this illustration. Each atom would still have a net charge of zero. + Hydrogen 2+ Helium 6. Possible answer: The electrons and protons can exist together in a single mass as shown below. The number of electrons and protons in each atom is equal. The atom is held together by the attraction between the positive protons and the negative electrons. 7. Electron Proton Neutron 8. a. The diameter of an atom is about 10–10 m. b. The diameter of the nucleus is about 10–15 m. Living By Chemistry Solutions Manual c. The size difference can be calculated by dividing the size of the atom by the size of the nucleus. 10 m _______ 1015 105 10 m 100,000 9. Possible answers: a. In the nuclear model, all of the electrons orbit the nucleus at the same distance. In the solar system model, the electrons orbit the nucleus at specific distances. b. In both models, negatively charged electrons revolve around a positively charged nucleus in circular orbits. Most of the atom is empty space. c. To change the solar system model to a more three-dimensional model, change some of the electron orbits so that they are orbiting the nucleus in different planes, similar to the way the nuclear model is drawn. 10. Possible answers: • Every compound is made of two or more elements in specific proportions that never change. Because these proportions are always the same, there must be a basic unit of each element. • In Rutherford’s experiment, alpha particles were deflected by particles in a sheet of gold foil. The gold must be made of concentrated bits of matter called atoms that contain mostly empty space. • Images of atoms have been made with powerful scanning tunneling microscopes. 11.No, the Greeks were not correct. It is now known that atoms are made of smaller particles such as electrons, protons, and neutrons. Each of these particles has a mass and a volume, so they are matter. 12.Possible answer: Although the atomic theory has existed for over 200 years, it has changed with the addition of new discoveries. Each new discovery leads to a new model that accounts for the new information about how atoms function. For example, the discovery of protons made it necessary to revise the nuclear model to account for small particles with a single unit of positive charge. Unit 1 Alchemy 9 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 9 4/16/12 3:32:02 PM Although the question does not call for the atomic theory as the basis for the example, it is the obvious choice within this section. Other examples, such as the theory of evolution, the theory of plate tectonics, or models of motion from Newton’s Laws to quantum mechanics, could show the scientific process equally well. Lesson 12 Exercises 1. The atomic number indicates the number of protons in the nucleus of an atom. 2. The atomic mass is the mass of an atom. If the mass is given in amu, then this number is equal to the number of protons and neutrons in the nucleus of the atom. 3. An atom that has 12 protons in its nucleus has an atomic number of 12. The periodic table indicates that element number 12 is magnesium. 4. The piece of information that identifies an element is its atomic number, or the number of protons in each atom of the element. The number of protons in the nucleus is a constant characteristic of all atoms of an element. 5. The atomic mass is the sum of the protons and the neutrons in the nucleus of an atom. Although boron and carbon each have six neutrons, carbon has six protons while boron only has five protons. 6. Element Sym. at. # #p #e #n amu nickel Ni 28 28 28 31 58.69 neon Ne 10 10 10 10 20.18 magnesium Mg 12 12 12 12 24.31 phosphorus P 15 15 15 16 30.97 zinc Zn 30 30 30 35 65.38 7. The information necessary to draw a model of a neon atom is contained in the table for Exercise 6. The model must show ten protons and ten neutrons in the nucleus. The electrons must be shown orbiting the nucleus. Two electrons must be located on the innermost orbit, and the other eight must be located on the outermost orbit. 8. From lowest to highest number of protons: • N: nitrogen, atomic number 7, 7 protons, 7 electrons, Group 5A • Na: sodium, atomic number 11, 11 protons, 11 electrons, Group 1A • Mg: magnesium, atomic number 12, 12 protons, 12 electrons, Group 2A • S: sulfur, atomic number 16, 16 protons, 16 electrons, Group 6A • Se: selenium, atomic number 34, 34 protons, 34 electrons, Group 6A • Sr: strontium, atomic number 38, 38 protons, 38 electrons, Group 2A Lesson 13 Exercises 1. Atomic number refers to the number of protons in the nucleus of an atom. Atomic mass, when expressed in amu, is the sum of the number of protons and the number of neutrons. 2. Possible answer: The mass of an atom in amu can be found by adding the number of protons to the number of neutrons in that particular atom. This number is always a whole number. The average atomic mass given on the periodic table is the average of the masses of all the isotopes in a large sample of that element. The periodic table in the textbook lists the average atomic mass to four significant digits. 3. Possible answer: The isotopes differ from one another in the number of neutrons in their nuclei. Each potassium isotope has 19 protons, but potassium-39 has 20 neutrons, potassium‑40 has 21 neutrons, and potassium‑41 has 22 neutrons. The isotopes 40 K, and 41 K. are 39 19 19 K, 19 4. a. Fluorine-23 has 9 protons, 14 neutrons, and 9 electrons. b. 59 Co has 27 protons, 32 neutrons, 27 and 27 electrons. 10 Unit 1 Alchemy LBC1eSM_01.indd 10 Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:02 PM c. Molybdenum-96 has 42 protons, 54 neutrons, and 42 electrons. 5. a. 58 amu 58 b. Fe 26 6. a. 30.97 amu b. 15 c. Because the average atomic mass is just slightly less than 31, a reasonable prediction is that the most common isotope is phosphorus-31. 7. Assume that a sample of 100 atoms would contain 76 chlorine-35 atoms and 24 chlorine-37 atoms. average atomic mass ______________ total mass number of atoms (76)(35 amu) + (24)(37 amu) ________________________ 100 35.48 amu 8. Assume that a sample of 1000 atoms would contain 76 lithium-6 atoms and 924 lithium-7 atoms. average atomic mass ______________ total mass number of atoms (76)(6 amu) + (924)(7 amu) _______________________ 1000 6.920 amu 9. Nitrogen has an atomic number of 7. The only isotope symbol of the three choices that has N. an atomic number of 7 is 14 7 The correct answer is B. Lesson 14 Exercises 1. Possible answer: An element is a fundamental building block of matter. An atom is the smallest possible unit of an element. An atom is the smallest unit of an element that still has the same characteristics as the element. 2. Possible answer: An isotope is an atom with a specific number of protons and neutrons. The word atoms can refer to a group of atoms with different mass numbers. 3. Stable isotopes are the black and pink boxes on the graph in the textbook that show isotopes for the first 95 elements. • Oxygen has 3 stable isotopes. • Neodymium has 5 stable isotopes. Living By Chemistry Solutions Manual • Copper has 2 stable isotopes. • Tin has 10 stable isotopes. 4. For each isotope, determine the number of protons and neutrons in the isotope. Then look at the corresponding coordinates on the graph showing isotopes for the first 95 elements to see if there is either a black box, pink box, or a white box. If a box is present, then the element is found in nature. Mg. • A black box at (12, 12) represents 24 12 Br. • A pink box at (35, 46) represents 81 35 Nd. • No box is present at (60, 92) for 152 60 Pt. • A black box at (78, 117) represents 195 78 238 • A white box at (92, 146) represents 92U. Uranium-238 is naturally occurring even though it is not stable. 5. The diagonal line on the graph represents isotopes that have equal numbers of protons and neutrons, because the line passes through points that have the same x- and y-coordinate. 6. a. Possible answer: helium-4, 42He; 10 O boron-10, B; and oxygen-16, 16 5 8 Any three isotopes that fall on the diagonal line are acceptable. The mass number will be twice the atomic number. 40 b. Possible answer: calcium-40, and 20Ca 42 calcium-42, Ca 20 Any two isotopes that have the same atomic number, representing the same element, are acceptable. 19 c. Possible answer: fluorine-19, and 9F 20 neon-20, 10Ne Any two isotopes with the same variation between their mass number and atomic number are acceptable. Zn d.Possible answer: zinc-70, 70 and 30 70 germanium-70, 32Ge Any two isotopes with the same mass number are acceptable. Unit 1 Alchemy 11 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 11 4/16/12 3:32:02 PM Ca 7. No stable isotopes exist beyond 40 20 that have equal numbers of protons and neutrons. The assumption must be made that a stable isotope would occur naturally if it existed (and therefore be plotted on the graph of the isotopes of the first 95 elements). 8. Oxygen-16 Oxygen-17 proton neutron electron proton neutron electron The possible elements are technetium (atomic number 43), promethium (atomic number 61), and any elements with an atomic number greater than 83 except thorium (atomic number 90). Each ratio is determined by dividing the number of neutrons by the number of protons. 10.Stable elements with 90 neutrons can have 62, 63, 64, or 66 protons. These elements are samarium, europium, gadolinium, and dysprosium. The assumption must be made that a stable isotope would occur naturally if it existed. 11.No, an isotope with 60 protons and a mass of 155 would have 95 neutrons. The graph of isotopes of the first 95 elements indicates that there is not a stable isotope that has 60 protons and 95 neutrons. 12.According to the graph of isotopes of the first 75 95 elements is an isotope of arsenic that 33Ar 112 ? are not ?, and 260 occurs in nature. 162 88 63 56?, likely to occur in nature. 13. C Oxygen-18 proton neutron electron 14. B Lesson 15 Exercises 1. A nuclear reaction is a change in the nucleus of an atom. Each drawing should have 8 protons and 8 electrons, 2 in the inner orbit and 6 in the outer orbit. The only difference should be in the number of neutrons represented in the nucleus. 9. Possible answer: • polonium: polonium-209 (1.49) and polonium-210 (1.50) • astatine: astatine-210 (1.47) and astatine-211 (1.48) • radon: radon-211(1.45), radon-220 (1.56), and radon-222 (1.58) • francium: francium-223 (1.56) • radium: radium-223 (1.53), radium-224 (1.55), radium-226 (1.57), and radium-228 (1.59) 12 Unit 1 Alchemy LBC1eSM_01.indd 12 2. Possible answer: In alpha decay, a nucleus emits a particle made up of two protons and two neutrons. In beta decay, a nucleus emits an electron. In alpha decay, the atomic number decreases by two and the atomic mass decreases by four. In beta decay, the atomic number increases by one and the atomic mass remains unchanged. 3. Possible answer: Gamma radiation is the most harmful because it has the most power to penetrate into living tissues and cause damage. This answer can be inferred from the diagram that shows the penetrating power of different kinds of radioactive decay. However, alternate answers are also acceptable. Alpha radiation is very dangerous if an alpha-emitting substance is ingested. Beta radiation can ionize atoms, while gamma radiation cannot, and ionization of body materials can lead to severe damage. Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:03 PM 4. The mass of the atom changes during alpha decay because the nucleus loses two neutrons and two protons, which have a combined mass of 4 amu. 5. The mass of the atom does not change during beta decay. The nucleus loses one electron, which has a mass that is a tiny fraction of the mass of the nucleus. The conversion of a neutron into a proton does not change the mass because neutrons and protons have nearly identical masses. 6. The alpha particle is emitted from the nucleus and consists only of protons and neutrons. Because it has two positively charged particles but no negatively charged particles, the alpha particle has a net positive charge of 2 and is not a neutral atom. 42 7. A. calcium-42, ✓ 20Ca 131 B. xenon-131, ✓ 54Xe Mg C. magnesium-24, 24 ✓ 12 52 D. cobalt-52, 27Co Os 8. A. osmium-171, 171 76 ✓ Sm B. samarium-145, 145 ✓ 62 Np C. neptunium-237, 237 ✓ 93 228 D. radium-228, 88Ra 9. The age of an object can be determined by the amount of carbon-14 found in a sample of the object relative to the amount of stable carbon in the sample. Objects that can be dated using carbon dating are composed partially of carbon, which means that they are usually the remains of living organisms. The wooden blade of the axe, the ashes, and the jawbone originated in living organisms. The clay pot and the arrowhead are both composed mainly of other elements. 10.Possible answer: According to the graph of the radioactive decay of carbon-14, 67% of the original amount of carbon-14 will remain after about 3500 years. Sources of error in this determination are the ability to read the data value on the graph, the measurement of the amount of carbon-14 remaining in the sunken ship, and the contamination of the sample due to being underwater for thousands of years. Living By Chemistry Solutions Manual 11. C 12. C Lesson 16 Exercises 1. Possible answers (any 4): • In alpha decay, a nucleus emits a particle consisting of two protons and two neutrons. The atomic number decreases by two and the atomic mass decreases by four. • In beta decay, a nucleus emits an electron. The atomic number increases by one as one of the neutrons becomes a proton. The atomic mass does not change. • I n nuclear fission, a nucleus splits apart to form the nuclei of two or more lighter elements. • In nuclear fusion, two nuclei combine to form the nucleus of a heavier element. • Nucleosynthesis is the process of forming elements inside stars through nuclear chemistry. • A nuclear chain reactions is a series of nuclear reactions when particles emitted by one fission reaction strike other nuclei. 2. A nuclear chain reaction is a sequence of nuclear fission reactions occurring when a particle strikes a nucleus causing it to break apart and form more particles that strike other nuclei, breaking them apart. 3. The atomic number of cerium, Ce, is 58. Beta decay increases the atomic number by one, forming praseodymium, Pr. The atomic mass does not change. 141 141 Ce 0e 58 → 1 59Pr 4. The atomic number of platinum, Pt, is 78. Alpha decay decreases the atomic number by two, forming osmium, Os. The atomic mass decreases by four, from 191 to 187. 191 Pt 78 Os → 4 2He 187 76 4 Cr Fe 5. Possible answer: 50 → 54 24 2He 26 The two nuclei chosen for the example must have atomic numbers and atomic masses that sum to the atomic number of iron, which is 26, and atomic mass of iron-54, which is 54. 6. a. The addition of a neutron to uranium-235 is 1 U U. shown by the equation 235 → 236 92 0n 92 Unit 1 Alchemy 13 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 13 4/16/12 3:32:03 PM b. Krypton-94 has 36 protons and barium-139 has 56 protons. c. A uranium atom has 92 protons and the reaction products have 92 protons, so no protons were lost. 7. Possible answer: Inside a nuclear power plant, uranium-235 is concentrated into rods and submerged in water. The atoms break apart when a neutron strikes them. More neutrons are produced during the reaction and they strike other uranium-235 atoms. These fission reactions produce heat that is used to convert water into steam. The steam turns a turbine to generate electric power. Control rods are made of material that absorbs the neutrons without breaking apart. Raising and lowering the rods in the water controls the rate of the nuclear reactions by changing the amount of neutrons absorbed. Section III Review Questions 1. Possible answer: An atom changes identity when the number of protons in its nucleus changes. Processes in which this can occur are radioactive decay, fission, and fusion. In radioactive decay, emission of an alpha particle decreases the atomic number by two, while emission of a beta particle increases the atomic number by one. Nuclear fission is the process in which a nucleus breaks apart, forming two or more smaller nuclei. In nuclear fusion, two nuclei join together to form one larger nucleus. 2. Possible answer: Elements are formed in nature by nuclear fusion. Most of the elements found on Earth are the products of fusion reactions in stars that exploded billions of years ago. After forming, these elements can decay into other elements through radioactive decay. 3. The atomic number of cadmium, Cd, is 48. Beta decay increases the atomic number by one, forming indium, In. The atomic mass does not change. 113 Cd 48 14 Unit 1 Alchemy LBC1eSM_01.indd 14 In → 1 0e 113 49 4. Possible answer: The atomic number of copper is 29 and the atomic number of gold is 79. Gold only has one naturally occurring stable isotope, which is gold-197. The most common isotope of copper is copper-63. Start by writing the equation. 63 Cu 29 197 ? ? ? → 79 Au The unknown element must have an atomic number of 79 29 50 and a mass number of 197 63 134. Tin, Sn is the element whose atomic number is 50. 197 63 134 Cu → 29 50Sn 79 Au The equation above is not plausible because tin-134 is not a naturally occuring isotope of tin. Copper cannot be fused directly with another atom to make gold because there is no combination of isotopes of copper and tin that have enough neutrons to form a stable isotope of gold. Project: Nuclear Power A good report would include • a description of how a nuclear reaction produces energy • a description of how the heat product in nuclear reactions is converted into electricity • a drawing of the inside of a reactor core and how the steam turns a turbine inside a generator • a list of the advantages and disadvantages of nuclear power when compared to fossil fuels and alternative energy sources • an opinion on whether nuclear power will be and should be an important source of energy in the future Lesson 17 Exercises 1. The color of the flame produced during a flame test is a characteristic of particular metallic elements. When a compound containing one of the metallic elements is heated, its atoms emit light of a specific color. 2. When a compound is heated, some of the electrons in the metallic atoms gain energy and move farther away from the nucleus. When the electrons move back to their original distance, they release energy in the form of colored light. Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:03 PM 3. Possible answer: Fireworks are colorful because they are made using metallic compounds that emit visible light during the explosions. Electrons of the metal atoms become excited when they are heated and the atoms release energy as light when the electrons return to their original state. Salts of various metals produce the range of fireworks colors: • red: lithium or strontium • orange: calcium • yellow: sodium • green: barium • blue: copper 4. The flame for sodium hydroxide will be yelloworange because the metal atom determines the color. Sodium atoms emit a yellow-orange color when placed in a flame. 5. Possible answers (any 2): • Red fireworks could contain lithium chloride and purple fireworks could contain a mixture of lithium chloride and copper chloride. • Red fireworks could contain lithium sulfate and purple fireworks could contain a mixture of lithium sulfate and copper sulfate. • Red fireworks could contain lithium nitrate and purple fireworks could contain a mixture of lithium nitrate and copper nitrate. A red color in fireworks would result from using a lithium salt. A purple color would result by mixing compounds that would produce red and blue colors separately. Any mixture of lithium and copper salts would produce purple fireworks. 6. Possible answer: The Lab: Flame Tests involved the performance of a flame test on five different compounds containing copper: copper nitrate, copper sulfate, copper chloride, copper wire, and a copper-coated penny. Each compound produced a blue-green flame when heated by the Bunsen burner. Since the presence of copper is the only thing these compounds have in common, the copper is responsible for the blue-green flame. 7. No, the flame color of each nitrate compound is different and matches the flame color of the metal in the compound. This indicates that the nitrate is not responsible for the color of the flame. Living By Chemistry Solutions Manual 8. No, the form of the sodium chloride does not affect the results of the flame test because the atoms do not emit light until they become very hot. The water will evaporate from the aqueous solution before the sodium chloride becomes hot enough to emit light. 9. The flame color produced by each compound can be determined by matching the metallic element in the compound with the flame color produced by compounds with that element. a. yellow-orange b. green c. pink-lilac d. pink-lilac e. green 10. C 11. D Lesson 18 Exercises 1. For main group elements, the number of shells containing electrons is equal to the period number. All of the shells, except the highest, are completely filled. The group number determines the number of electrons in the outermost shell. 2. For elements in the main group, the number of valence electrons is equal to the group number. 3. Possible answer: Beryllium, magnesium, and calcium are all alkaline earth metals located in Group 2A. These three elements have similar chemical and physical properties because they have two valence electrons. 4. Core electrons 5 Valence electrons Boron has an atomic number of 5, so it has five total electrons. Boron is a Group 3A element in the second period of the periodic table, so it has three valence electrons in the second shell. The first shell is filled with two core electrons. Unit 1 Alchemy 15 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 15 4/16/12 3:32:03 PM 5. The number of core electrons does not change across a period for main group elements. 6. a. Carbon has 6 electrons and silicon has 14 electrons. b. 6 Carbon 14 Silicon c. Carbon and silicon both have 4 valence electrons. d. Carbon has 2 core electrons and silicon has 10 core electrons. e. Carbon and silicon have similar properties because atoms of the two elements have the same number of valence electrons. 7. a. Element number 17 is chlorine. It has the chemical symbol Cl and is located in Group 7A. This information comes directly from square 17 on the periodic table. b. The nucleus contains 17 protons. The number of protons is equal to the atomic number. c. Possible answer: The average atomic mass of chlorine to the nearest whole number is 35 amu. Therefore, the nucleus will have 35 17 18 neutrons. According to the graph of isotopes of the first 95 elements, chlorine-35 is a naturally occuring isotope. d. The number of electrons in a neutral atom of chlorine is 17. In a neutral atom, the number of electrons equals the number of protons. e. Chlorine has 7 valence electrons. The number of valence electrons is equal to the group number. f. Chlorine has 10 core electrons. The number of core electrons equals the difference between the total number of electrons and the number of valence electrons, or 17 7. g. Possible answer (any 3 elements): Fluorine, bromine, iodine, and astatine all have the same number of valence electrons. All of these elements are in Group 7A along with chlorine. 16 Unit 1 Alchemy LBC1eSM_01.indd 16 8. a. Element number 50 is tin. It has the chemical symbol Sn and is located in Group 4A. This information comes directly from square 50 on the periodic table. b. T he nucleus contains 50 protons. The number of protons is equal to the atomic number. c. Possible answer: The average atomic mass of tin to the nearest whole number is 119 amu. Therefore, the nucleus will have 119 50 69 neutrons. According to the graph of isotopes of the first 95 elements, tin-119 is a naturally occuring isotope. d. The number of electrons in a neutral atom of tin is 50. In a neutral atom, the number of electrons equals the number of protons. e. T in has 4 valence electrons. The number of valence electrons is equal to the group number. f. Tin has 46 core electrons. The number of core electrons equals the difference between the total number of electrons and the number of valence electrons, or 50 4. g. Possible answer (any 3 elements): Carbon, silicon, germanium, and lead all have the same number of valence electrons. All of these elements are in Group 4A along with tin. 9. E 10. B Lesson 19 Exercises 1. A cation is an ion that has a positive charge. An anion is an ion that has a negative charge. 2. Noble gas envy is a term referring to the tendency of atoms to gain or lose electrons to obtain an electron configuration in which the outer shell is completely filled. Noble gases are the only elements with their outer shells completely filled in their neutral state. 3. The atomic number of lithium is 3, so Li+ has 3 protons. Li+ is a cation formed when a lithium atom loses one of its electrons, so Li+ has 2 electrons. The average atomic mass of lithium to the nearest whole number is 7 amu. Therefore, the nucleus will have 7 3 4 neutrons. According to the graph of isotopes of the first 95 elements, lithium-7 is a naturally occuring isotope. Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:04 PM 4. Possible answer: Cl and Cl– are similar in that they both have the same number of protons and the same number of neutrons. But, Cl has 17 electrons and Cl– has 18 electrons. Cl is more reactive because it is missing an electron in its valence shell, while Cl– is more stable because it has a full valence shell. 5. Possible answer: Be and Be2+ are similar in that they have the same number of protons and the same number of neutrons. But, Be has four electrons and Be2+ has two electrons. Be is more reactive because it has only two electrons in its valence shell, while Be– is more stable because it has a full valence shell. 6. The noble gas closest to magnesium is neon. A magnesium atom loses two electrons to have an electron arrangement similar to that of neon. The closest noble gas may be in a different period of the table, as shown in this exercise. Neon has two fewer electrons than magnesium, but argon, the noble gas in the same period as magnesium, has six more electrons. 7. The noble gas closest to sulfur is argon. A sulfur atom gains two electrons to have an electron arrangement similar to that of argon. 8. Possible answers (any 4): N3–, O2–, F–, Na+, Mg2+, Al3+ The elements that are close to neon on the periodic table gain or lose electrons to have the same electron structure as neon. 9. Possible answers (any 4): P3–, S2–, Cl–, K+, Ca2+ The elements that are close to argon on the periodic table gain or lose electrons to have the same electron structure as argon. 10.Arsenic is a Group 5 element so it has 5 valence electrons. It will form an ion by adding three electrons to have the same electron arrangement as krypton. It has a charge of 3–. The symbol for the arsenic ion is As3–. 11.The element that has 22 protons is identified on the periodic table as titanium, Ti. Because the ion has 22 protons and 18 electrons, it has a net positive charge of 4. The number of neutrons is not needed in order to determine the ion. 12.When chlorine gains an electron, it does not become an argon atom because the ion still has 17 protons. It is the number of protons that determines the identity of the element. Living By Chemistry Solutions Manual 13.Elements on the right side of the table gain electrons to have a noble gas arrangement. They do not tend to lose electrons because the charge would be too large. 14.In each period, ions on the left side have a positive charge that increases toward the center of the table. On the right side, ions have a negative charge, which increases from the second row from the right toward the center. The element at the far right of a period does not form ions. 15. B, D, and E 16. A, B, and E Lesson 20 Exercises 1. The number of valence electrons can be used to predict whether an atom will form a cation or an anion, as well as the charge on the ion. Ionic compounds form between cations and anions in a ratio where the charges are balanced. 2. The rule of zero charge can be used to predict the ratio of ions that will form a compound that has no overall charge. 3. a. 1 b. 3 c. Lithium nitride has three lithium ions with a charge of 1 and one nitride ion with a charge of 3. 3(1) (3) 3 (3) 0 d. Lithium has 1 valence electron. Nitrogen has 5 valence electrons. So there are a total of 8 valence electrons in Li3N. 4. a. 3 b. 3 c. Aluminum arsenide has one aluminum ion with a charge of 3 and one arsenide ion with a charge of 3. (3) (3) 0 d. Aluminum has 3 valence electrons. Arsenic has 5 valence electrons. 5. a. KBr has one potassium ion with a charge of 1 and one bromide ion with a charge of 1. (1) (1) 0 b. CaO has one calcium ion with a charge of 2 and one oxide ion with a charge of 2. (2) (2) 0 Unit 1 Alchemy 17 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 17 4/16/12 3:32:04 PM c. Li2O has two lithium ions with a charge of 1 and one oxide ion with a charge of 2. 2(1) (2) 2 (2) 0 d. CaCl2 has one calcium ion with a charge of 2 and two chloride ions with a charge of 1. (2) 2(1) 2 (2) 0 e. AlCl3 has one aluminum ion with a charge of 3 and three chloride ions with a charge of 1. (3) 3(1) 3 (3) 0 6. a. Potassium, K, has 1 valence electron. Bromine, Br, has 7 valence electrons. b. Calcium, Ca, has 2 valence electrons. Oxygen, O, has 6 valence electrons. c. Lithium, Li, has 1 valence electron. Oxygen, O, has 6 valence electrons. d. Calcium, Ca, has 2 valence electrons. Chlorine, Cl, has 7 valence electrons. e. Aluminum, Al, has 1 valence electron. Chlorine, Cl, has 7 valence electrons. 7. All three compounds violate the rule of zero charge. a. NaCl2 does not form because it has a net charge of 1. The sodium ion has a charge of 1 and each chloride ion has a charge of 1. (1) 2(1) 1 (2) 1 b. CaCl does not form because it has a net charge of 1. The calcium ion has a charge of 2 and the chloride ion has a charge of 1. (2) (1) 1 c. AlO does not form because it has a net charge of 1. The aluminum ion has a charge of 3 and the oxide ion has a charge of 2. (3) (2) 1 Lesson 21 Exercises 1. For main group elements, the group number shows the number of valence electrons. • Metal atoms lose all of their valence electrons when they form an ion, adding a positive charge for each electron lost. • Nonmetal atoms gain enough electrons to have eight valence electrons, adding one negative charge for each electron gained. 18 Unit 1 Alchemy LBC1eSM_01.indd 18 2. For main group elements, the periodic table is used to determine the charge on each ion. Ions combine to form ionic compounds in ratios that have a total charge equal to zero. 3. a. LiCl is possible because the total of the charges on the ions equals zero. The lithium ion has a charge of 1 and the chloride ion has a charge of 1. (1) (1) 0 b. LiCl2 is not possible because the total of the charges on the ions equals 1. (1) 2(1) 1 (2) 1 c. MgCl is not possible because the total of the charges on the ions equals 1. Magnesium ions have a charge of 2. (2) (1) 1 d. MgCl2 is possible because the total of the charges on the ions equals zero. (2) 2(1) 2 (2) 0 e. AlCl3 is possible because the total of the charges on the ions equals zero. Aluminum ions have a charge of 3. (3) 3(1) 3 (3) 0 4. Possible answer (any 6): Sodium chloride, NaCl, has 8 valence electrons; Calcium oxide, CaO, has 8 valence electrons; Rubidium iodide, RbI, has 8 valence electrons; Potassium bromide, KBr, has 8 valence electrons; Sodium fluoride, NaF, has 8 valence electrons; Magnesium oxide, MgO, has 8 valence electrons; Strontium sulfide, SrS, has 8 valence electrons; Calcium sulfide, CaS, has 8 valence electrons. Any combination of a Group 1A metal with a Group 7A nonmetal, or a Group 2A metal with a Group 6A nonmetal, or a Group 3A metal with a Group 5A nonmetal is correct. 5. Possible answer (any 3): Sodium oxide, Na2O, has 8 valence electrons; Lithium oxide, Li2O, has 8 valence electrons; Rubidium sulfide, Rb2 S, has 8 valence electrons; Potassium sulfide, KS, has 8 valence electrons. Any combination of a Group 1A metal with a Group 6A nonmetal is correct. Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:04 PM 6. Possible answer (any 3): Magnesium chloride, MgCl2, has 16 valence electrons; Calcium fluoride, CaF2, has 16 valence electrons; Barium iodide, BaI2, has 16 valence electrons; Strontium bromide, SrBr2, has 16 valence electrons. Any combination of a Group 2A metal with a Group 7A nonmetal is correct. 7. a. AlBr3, aluminum bromide b. Al2S3, aluminum sulfide c. AlAs, aluminum arsenide d. Na2S, sodium sulfide e. CaS, calcium sulfide f. Ga2S3, gallium sulfide 8. a. Mg2+, O2−, MgO b. Rb+, Br−, RbBr c. Sr2+, I−, SrI2 d. Be2+, F−, BeF2 e. Al3+, Cl−, AlCl3 f. Pb4+, S2−, PbS2 Lesson 22 Exercises 1. A polyatomic ion is an ion that consists of two or more elements. 2. An ionic compound has a polyatomic ion if there are more than two elements in the compound. 3. a. ammonium chloride b. potassium sulfate c. aluminum hydroxide d. magnesium carbonate 4. a. Li2SO4 b. KOH c. Mg(NO3)2 d. (NH4)2SO4 5. The chemical formula of the cyanide ion must be CN because sodium, Na, forms the metal cation. Sodium is in Group 1A, so its ion has a charge of 1. Because the ions are combined in a 1:1 ratio, the cyanide ion must have a charge of 1. Living By Chemistry Solutions Manual 6. The chemical formula clearly shows PO4 as the polyatomic ion. Calcium, Ca, is in Group 2A, so it forms a cation with a charge of 2. The ions combine in a 3:2 ratio. Because the total charge on the cations is 3 (2) 6, the total charge on the anions should be −6. Each phosphate anion must have a charge of (6) 2 3. 7. B. KSO4 does not form because it has a net charge of 1. The potassium ion has a charge of 1 and the sulfate ion has a charge of 2. (1) (22) 1 Lesson 23 Exercises 1. The Roman numeral indicates the charge on the transition metal cation in the compound. 2. Determine the total charge on the anions in the compound. The total charge of the cations is the opposite of the charge on the anions. Divide by the number of cations in the chemical formula to find the charge of each cation. 3. a. 2, mercury (II) sulfide b. 2, copper (II) carbonate c. 2, nickel (II) chloride d. 3, cobalt (III) nitrate e. 2, copper (II) hydroxide f. 2, iron (II) sulfate 4. a. Cu2+, S2−, CuS b. Ni2+, NO3−, Ni(NO3)2 c. Fe2+, CO32−, FeCO3 d. Co2+, SO42−, CoSO4 e. Fe3+, CO32−, Fe2(CO3)3 f. Cr6+, O2−, CrO3 5. Co3(PO4)2 Lesson 24 Exercises 1. Electron subshells are divisions within a specific electron shell of an atom. 2. An electron configuration is a shorthand notation used to show the position of electrons within shells and subshells of an atom. Unit 1 Alchemy 19 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 19 4/16/12 3:32:04 PM 3. As the number of electrons in an element increases, they are added in a specific sequence that is illustrated by the position of the element on the periodic table. Each section of the table corresponds to a particular subshell of electrons. 4. • The shell n 1 has one subshell. • The shell n 2 has two subshells. • The shell n 3 has three subshells. • The shell n 4 has four subshells. The number of subshells that a shell n has is equal to n. 5. The sum of the subshells of the shells n 1, 2, 3, 4, and 5 is 1 2 3 4 5 15. 6. a. b. 10 11 c. d. 7. 4p 8. Possible answer: gold You can accept any element that has an atomic number of 57 or greater as a correct answer. 9. a. 1s2 2s22p63s23p1 b. Element 13 has 3 valence electrons because it has three electrons in the outer shell, n 3. c. Element 13 has 10 core electrons because it has two shells filled completely: n 1 with 2 electrons and n 2 with 8 electrons. 10.Argon, krypton, and xenon have similar properties because they all have the same number of valence electrons in their outermost shells. The additional core electrons do not affect the properties of the elements very much. LBC1eSM_01.indd 20 13. a. chromium d. cesium b. silicon e. lead c. nitrogen f. silver 1. Valence electrons are important because they are the outermost part of an atom and will interact with other atoms. This interaction is what determines the properties of an element. 6 Unit 1 Alchemy 12.Possible answer: Add the total number of electrons in the configuration and look up the atomic number. Find the location on the periodic table that corresponds to the end of the electron configuration. Section IV Review Questions 23 20 11. a. 1s22s22p4, [He] 2s22p4 b. 1s22s22p63s23p5, [Ne] 3s23p5 c. 1s22s22p63s23p64s23d6, [Ar] 4s23d6 d. 1s22s22p63s23p64s2, [Ar] 4s2 e. 1s22s22p63s2, [Ne] 3s2 f. 1s22s22p63s23p64s23d104p65s24d9, [Kr] 5s24d9 g. 1s22s22p63s23p2, [Ne] 3s23p2 h. 1s22s22p63s23p64s23d104p65s24d105p66s24f 14 5d10, [Xe] 6s24f 145d10 2. Ionic compounds are combinations of cations and anions that are bound together by the electrical attraction of their opposite charges. They form when electrons are transferred between atoms leaving each resulting ion with a noble gas arrangement. 3. As the number of electrons in an element increases, they are added in a specific sequence that is illustrated by the position of the element on the periodic table. Each section of the table corresponds to a particular subshell of electrons. 4. 1s22s22p63s23p1, [Ne] 3s23p1 5. a. The anion is Mg2+ and has a charge of 2. The cation is Cl− and has a charge of 1. b. The anion is Ca2+ and has a charge of 2. The cation is NO2− and has a charge of 1. 6. a. Na2SiO3, NaClO2, NaHCO3 b. CaSiO3, Ca(ClO2)2, Ca(HCO3)2 Lesson 25 Exercises 1. A substance is insoluble if it fails to dissolve in a particular solvent. The word insoluble does not imply that the solvent is water. A substance that does not dissolve in water is said to be insoluble in water. Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:05 PM 2. Possible answer: Electrical conductivity can be tested by setting up a simple electrical circuit. When the circuit is complete, a light bulb that is part of the circuit will light up. If the circuit is interrupted by a substance that does not conduct electricity, the light bulb will not light up. 3. Possible answer: The substance is most likely an ionic compound. Many compounds dissolve in water but electrical conductivity in solution is a characteristic of compounds that separate into ions, such as ionic compounds. Although there are exceptions, most ionic compounds dissolve in water. Ionic solutions always conduct electric current because the ions are mobile in the solution. 4. No, though ionic compounds generally contain metals, they do not conduct electricity in their solid form. Substances that are composed only of metals always conduct electricity. However, in a solid ionic compound, where a metal is bonded with a nonmetal, the charged ions are locked into position so they cannot move freely and carry electricity. 5. No, though ionic compounds generally do not conduct electricity as solids, they do conduct electricity as aqueous solutions. In solution, the ions of an ionic compound are able to move around, so they can carry electric charges from one place to another. 6. Possible answers: a. Acetone is not likely to conduct electricity either in solution or in its pure form because it does not contain any metallic elements. Acetone will probably dissolve in water because compounds composed only of carbon, hydrogen, and nitrogen usually dissolve in water. b. Titanium is a metallic element, so it conducts electricity and does not dissolve in water. c. Lithium nitrate is an ionic compound, so it dissolves in water and does not conduct electricity in its solid form. Once dissolved, it will conduct electricity. d. Bronze is a mixture that is composed only of metallic elements. Therefore, it conducts electricity and does not dissolve in water. Living By Chemistry Solutions Manual Lesson 26 Exercises 1. The atoms that make up substances are held together by chemical bonds. The bond is an attraction between the positively charged nuclei of atoms and the valence electrons of other atoms. 2. Possible answers: • In ionic bonding, one or more valence electrons are transferred from a metal atom or group of atoms to a nonmetal atom or group of atoms, forming a positively charged cation and a negatively charged anion. The bond forms due to the attraction of the opposite charges. • In metallic bonding, valence electrons from all of the metal atoms move freely among the cations that are formed when the electrons leave the metal atoms. The bond forms because of the attraction of the positively charged cations to the sea of negatively charged electrons. • In network covalent bonding, valence electrons from each nonmetal atom are shared with all of the atoms around it. The structure of the substance is very rigid since each atom bonds with multiple neighboring atoms. • In molecular covalent bonding, valence electrons from a nonmetal atom are shared with other individual atoms, forming groups with a specific number and arrangement of atoms, called molecules. 3. a. Because zinc consists entirely of metal atoms, it is held together by metallic bonds. b. Propane is made entirely of nonmetal atoms, so it is held together by molecular covalent bonds. c. Calcium carbonate consists of the metal calcium and the polyatomic ion carbonate. Therefore the compound is an ionic compound that is held together by ionic bonds. 4. Possible answer: A. Hair gel would probably consist of molecular covalent bonds. Hair gel is soft and malleable, dissolves in water, and is easily separated into smaller portions, so it is likely to be molecular. Unit 1 Alchemy 21 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 21 4/16/12 3:32:05 PM B. A silver bracelet has metallic bonds. A silver bracelet is made entirely of metal, so its atoms will be held together by metallic bonds. It is hard and bendable and conducts electricity. C. Motor oil would probably consist of molecular covalent bonds. Motor oil is a viscous liquid, and liquids that are not salts in an aqueous solution are usually molecular. D. Baking soda is the only one of these substances that could have ionic bonds. It is a solid crystalline material that dissolves easily in water. If it contains metal and nonmetal atoms, it is probably held together by ionic bonds. 5. NO2 is a gas that is made up of nonmetal atoms, so it has molecular covalent bonds. e. Copper sulfate, CuSO4, is an ionic compound, so it will dissolve in water. Lesson 27 Exercises 1. Possible answers (any 3): • finding pure metals in nature • heating ionic compounds to separate the metal • extracting metals with electricity • reusing and recycling discarded metals 2. Possible answer: Place two nickel strips in a beaker of copper chloride solution. Connect the strips to the two terminals of a battery. Allow the battery current to flow until the strip connected to the negative terminal of the battery has become plated with copper. Battery 6. E 7. Possible answer: Drop the mixture into a beaker of water. The ionic bonds of sodium chloride break apart in water, causing the solid to dissolve. Carbon, held together by network covalent bonds, does not dissolve in water, and so can be filtered from the solution. 8. Copper metal can be shaped into a wire easily because of its metallic bonds. Metals are malleable and ductile. Copper chloride, as an ionic compound, is brittle and cannot be shaped into a wire. The ions in copper chloride are held in position relative to one another by strong ionic bonds. 9. Carbon is a solid because many carbon atoms are held together in a large array by network covalent bonds, such as in diamond. Gases are single atoms or molecules held together by molecular covalent bonds. 10. Possible answers: a. Calcium, Ca, is held together by metallic bonding so it will not dissolve in water. b. Sodium nitrate, NaNO3, is an ionic compound, so it will dissolve in water. c. Silicon, Si, is a solid held together in a large array by network covalent bonds, similarly to carbon. It will not dissolve in water. d. Methane, CH4, is a liquid held together by molecular covalent bonds, so it will probably dissolve in water. 22 Unit 1 Alchemy LBC1eSM_01.indd 22 Nickel strips Copper deposits here Copper chloride solution Diagrams should include a voltage source (a battery), a solution of copper chloride with two nickel strips in it, and connections between each strip and one of the terminals on the battery. 3. Possible answer: Attach the coated object to the positive terminal of a battery in an electroplating circuit. When an object is attached to the positive terminal, electrons flow from the object, forming cations. The metal ions are no longer attracted to the coated object, and they enter the solution. 4. A good lab report will contain • a title (Lab: Electroplating) • a statement of purpose (Possible answer: To demonstrate how metals can be extracted from an ionic compound dissolved in water) • a procedure (a summary of the steps followed in the experiment) Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:05 PM • results (Check student observations to make sure they address all of the observation questions in the lab.) • a conclusion (The conclusion should include a statement about the attraction of the metal cations to the metal strip. Possible answer: When an ionic compound is dissolved in water, running an electric current through two metal strips and the solution will cause the metal cations to deposit on the negatively charged metal strip.) 5. The copper sulfate solution is composed of cations, Cu2+, and anions, SO4−, dissolved in water. The only thing that is added to the solution during the experiment is a stream of electrons. When the electrons are added to the copper ions, copper atoms, Cu, are formed on the metal strip. This indicates that the Cu2+ ions are simply copper ions that are missing electrons. 6. Possible answer: The mass of the negatively charged nickel strip should increase as it is plated with copper. There is no change to the nickel itself, but as a layer of copper forms on top of the nickel, the mass will increase by the mass of the copper plating. 7. Possible answer: Nickel cannot change into copper unless the number of protons in the nucleus changes. The plating apparatus only adds electrons to the nickel strip, causing the plating to occur. Adding electrons does not change the nucleus, so it cannot change the identity of the atoms. You cannot be sure simply from observation that the strip is copper-coated nickel and not pure copper. Reversing the experiment only proves that the copper appears and disappears on the strip. Observations must be taken into account along with knowledge about the structure of atoms. Taking the copper-plated strip and cutting it or measuring its density to prove that the nickel is still there is not a valid answer because it does not explain why the nickel had to remain intact. Section V Review Questions 2 . Possible answer: Determine whether the material conducts electric current, whether it dissolves in water, and if it does, whether the solution conducts electric current. • If a material does not conduct electricity unless it is in solution, it has ionic bonding. • If a material conducts electricity but does not dissolve, it has metallic bonding. • If a material does not conduct electricity even when in solution, it has molecular covalent bonding. • If a material does not conduct electricity and does not dissolve, it has network covalent bonding. These are only general guidelines and there are exceptions to the rules listed above. 3. Possible answer: Isopropanol will not conduct electricity because compounds with only nonmetal atoms have covalent bonding and do not conduct electricity. Also, isopropanol is a liquid at room temperature, which means it is not an ionic compound. 4. Dissolves Does not dissolve Conducts ionic (conducts in solution) metallic Does not conduct molecular covalent molecular covalent network covalent Molecular covalent bonds appear in two boxes because some molecular compounds dissolve and others do not. Unit 1 Review Exercises 1. Possible answer: An element is the basic building block of compounds. An element has only one type of atom, while a compound has at least two types of atoms held together by chemical bonds. An alternative answer is that a compound can be broken down into simpler substances, but an element cannot. 1. Possible answer: While it is not practical to try to make gold, many substances that are quite valuable can be made through chemistry. Living By Chemistry Solutions Manual Unit 1 Alchemy 23 © 2012 W. H. Freeman and Company/BFW LBC1eSM_01.indd 23 4/16/12 3:32:06 PM 2. D __ m , so V m __ V m • __ 1 D D lead: V 20.0 g • _____ 1 mL 1.75 mL 11.4 g aluminum: V 20.0 g • _____ 1 mL 7.41 mL 2.7 g The aluminum object takes up more space. 3. a. Lithium, Li, has atomic number 2 and is in Group 2A. It has 2 protons and 2 electrons. b. Bromine, Br, has atomic number 35 and is in Group 7A. It has 35 protons and 35 electrons. c. Zinc, Zn, has atomic number 30 and is in Group 2B. It has 30 protons and 30 electrons. d. Sulfur, S, has atomic number 16 and is in Group 6A. It has 16 protons and 16 electrons. e. Barium, Ba, has atomic number 56 and is in Group 2A. It has 56 protons and 56 electrons. f. Carbon, C, has atomic number 6 and is in Group 4A. It has 6 protons and 6 electrons. 4. Nuclear fission occurs when a nucleus breaks apart to form two nuclei with smaller atomic numbers than the original nucleus. Nuclear fusion occurs when two nuclei join together to form a nucleus with a greater atomic number. 5. An isotope is an atom of an element with a specific number of neutrons in its nucleus. You can predict the most common isotope by rounding the average atomic mass of the element to the nearest whole number. For some elements having multiple isotopes that are found in nature, the average atomic mass does not reflect the common isotope. However, the procedure described above is the best for predicting the common isotope using only the periodic table. 6. Possible answer: • If both atoms are metal atoms, then the atoms will form a metallic bond. • If one atom is a metal and the other atom is a nonmetal, then the two atoms might form an ionic bond. • If both atoms are nonmetal atoms, then the atoms might form a covalent bond. • If either atom is a noble gas, the atoms will probably not form any bond. 24 Unit 1 Alchemy LBC1eSM_01.indd 24 7. Cations are ions that have lost electrons, causing them to have a positive charge. Anions are ions that have gained electrons, causing them to have a negative charge. 8. • metals: Na, Sr, Mg, Cu • nonmetals: S, Cl, Se, I • Possible answer (any 3): sodium chloride, NaCl; magnesium iodide, MgI2; strontium sulfide, SrS; and copper (II) chloride, CuCl2. Any combination of metal and nonmetal elements can be examples of ionic compounds as long at the ratio of metal to nonmetal in the chemical formula indicates that the charge is equal to zero. The name of any copper compound must include the charge on the copper cation. 9. a. Aluminum is a metal and chlorine is a nonmetal, so aluminum chloride has ionic bonding and conducts electricity in solution only. b. Oxygen is made up only of nonmetal atoms and is a gas, so it has molecular covalent bonding and does not conduct electricity. c. Silver (I) hydroxide has ionic bonding and conducts electricity in solution only. d. Platinum is a metal element, so it has metallic bonding and conducts electricity. 10.Possible answer: You can determine the charge on a transition metal ion by the formula of its salt. The total charge of the ionic compound must be zero, so the positive charge on the metal ion is the sum of the negative charges on the anions divided by the number of metal ions in the formula. 11.A material that does not dissolve in water and does not conduct electricity is held together by network covalent bonds or molecular covalent bonds. Although some materials with molecular covalent bonds dissolve in water, others do not. 12.One element can be changed into another only by changing the number of protons in the nuclei of its atoms. This process requires enormous amounts of energy. Living By Chemistry Solutions Manual © 2012 W. H. Freeman and Company/BFW 4/16/12 3:32:06 PM
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