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mad17743_ch02.qxd 3/10/06 1:48 PM Page 8 PART I THE CELL 2 THE CHEMICAL BASIS OF LIFE CHAPTER REVIEW This chapter introduces you to chemistry, or specifically, the study of the structure of atoms and how they react with one another. Water is so important to living things that the structure of H 2 O, in particular, is studied along with the differences between acid and basic solutions. CHAPTER KEY TERMS After studying the key terms of this chapter, match the phrases below with the alphabetized list of terms. acid hydrophobic atom ion base octet rule buffer pH scale covalent bond polar electron proton hydrophilic a. more H than OH _______________________ b. water loving _______________________ c. water hating _______________________ d. unit of an element _______________________ e. more OH than H _______________________ f. negatively charged subatomic particle _______________________ g. positively charged subatomic particle _______________________ h. negatively or positively charged atom _______________________ i. molecule that has a negative/positive region _______________________ j. maintains pH constant _______________________ k. atoms share pair of electrons _______________________ l. stable atoms have eight electrons in outer shell _______________________ m. numbers indicate acidity/basicity of solution _______________________ 8 mad17743_ch02.qxd 3/10/06 1:48 PM Page 9 S T U DY E X E R C I S E S Study the text section by section as you answer the questions that follow. 2.1 THE NATURE • • • • • OF MATTER (PP. 16–21) Matter is composed of 92 naturally occurring elements, each composed of atoms. Atoms have subatomic particles: neutrons, protons, and electrons. Atoms of the same type that differ by the number of neutrons are called isotopes. Atoms react with one another by giving up, gaining, and sharing electrons. Bonding between atoms results in molecules with distinctive chemical properties and shapes. 1. Name the six elements commonly found in living things. ____________________________________________________ _____________________________________________________________________________________________________________ 2. An element has nine protons and nine neutrons in each of its atoms. Its atomic number is a. _______________, its atomic mass is b. _________________, and the number of electrons in this atom is c. ________________. 3. In the periodic table of chemical elements, the horizontal rows are called a. _______________ and the vertical columns are called b. _______________. The atoms in group 8 are called the c. _______________ because they d. _______________ react with other atoms. 4. Isotopes have the same atomic a. _______________, but they differ in the number of b. _______________. 5. At least two forms of the oxygen atom exist in the environment: 168 O and 188 O. a. Both atoms have eight electrons. 8 16 O and 8 18 O are _________________ of the element oxygen. b. The numbers 16 and 18 represent _________________. c. The atomic number of d. The atomic number of 8 16 O 8 18 O is _________________. is _________________. 8 16 O is __________________. of 188 O is __________________. e. The number of protons in the atom of f. The number of neutrons in the atom g. How do 168 O and 188 O differ in number of subatomic particles? _________________. 6. Complete the following table with the correct numbers: Isotope Protons Neutrons Atomic Number Atomic Mass 6 12 C 6 14 C 15 31 P 15 33 P 7. Indicate whether these statements are true (T) or false (F): a. A neutral atom has the same number of protons and electrons. b. The number of electrons in the outer shell determines the atom’s chemical properties. c. The electrons of an atom are located in energy levels (electron shells) at varying distances from the nucleus. d. Electrons in the first shell possess more energy than do electrons in the second shell. 8. An atom of an element with an atomic number of 9 has a. ______________ electrons in its first shell and b. ______________ electrons in its second shell. 9 mad17743_ch02.qxd 3/10/06 1:48 PM Page 10 9. An atom of the element neon (Ne) has eight electrons in its outer shell. An atom of the element sulfur (S) has six electrons in its outer shell. a. Which atom is reactive? ______________ b. Which atom is inert? ______________ c. Why is there a difference in the reactivity of these two elements? _____________________________________ _________________________________________________________________________________________________ 10. The magnesium atom has an atomic number of 12 and an atomic weight of 24. Draw its simplified atomic structure. Draw small circles to indicate the general distribution of electrons in concentric levels around the nucleus. In the nucleus, indicate the number of protons and neutrons. 11. Calcium (Ca) has an atomic number of 20; chlorine (Cl) has an atomic number of 17. a. The number of electrons in the outer shell of calcium is ______________. b. The number of electrons in the outer shell of chlorine is ______________. c. In a chemical reaction between these two atoms, ______________ calcium atom(s) will react with ______________ chlorine atom(s). d. Which element will gain electrons in this reaction? ______________ e. What will its charge be after the reaction? ______________ f. Which element will lose electrons in this reaction? ______________ g. What will its charge be after the reaction? ______________ h. What type of bond forms between these two atoms? ______________ i. Write the formula for the compound produced through this chemical reaction. ______________ 12. Water is a polar molecule. a. Indicate on the following diagram which atoms are electronegative ( – ) and which are electropositive ( + ) in relation to the others. Put – charges and + charges where appropriate. b. Label a hydrogen bond. 10 mad17743_ch02.qxd 3/10/06 1:48 PM Page 11 13. Place the appropriate letter next to each statement. C—covalent bonding I—ionic bonding H—hydrogen bonding a. Electrons transfer between atoms. b. Atoms share electrons. c. This bond is present in Na Cl . d. This bond is present in the O 2 molecule. e. The hydrogen atom in one molecule is attracted to the oxygen atom of another molecule. 2.2 WATER’S IMPORTANCE TO LIFE (PP. 22–26) • The existence of organisms is dependent on the chemical and physical properties of water. • Organisms are sensitive to the hydrogen ion concentration [H ] of solutions, which can be indicated using the pH scale. 14. In each of the pairs of statements that follow, place a check next to the one that correctly describes how hydrogen bonding affects the properties of water. Hydrogen bonding causes water: Pair 1 a. to boil at a lower temperature than expected. b. to boil at a higher temperature than expected. Pair 2 c. d. to be more dense as ice than as liquid water. to be less dense as ice than as liquid water. Pair 3 e. f. to absorb heat with a minimal change in temperature. to absorb heat with a maximum change in temperature. Pair 4 g. to be cohesive—the water molecules cling to each other. h. molecules to shun one another. 15. Refer to the chemical properties of water when answering the following questions: a. What makes water a good solvent? _______________________________________________________________ _______________________________________________________________________________________________ b. How does water moderate temperatures? __________________________________________________________ _______________________________________________________________________________________________ c. What allows ice to float on liquid water? __________________________________________________________ _______________________________________________________________________________________________ 16. Place the appropriate letter next to each statement. A—acid B—base a. They take up hydrogen ions in solution. b. HCl is an example. c. NaOH is an example. d. They release hydrogen ions in solution. e. They lower the pH. f. They raise the pH. 17. Complete the table for the following hydrogen ion concentrations [H + ]: [H + ] pH Acid/Base/Neutral 1 10 –7 1 × 10 –3 1 × 10 –8 11 mad17743_ch02.qxd 3/10/06 1:48 PM Page 12 18. Indicate whether these statements are true (T) or false (F): a. If the pH of blood changes from 7.4 to 7.6, it becomes more acidic. b. When an acid is added to a solution, the pH decreases. c. A basic pH indicates that OH – ions outnumber H + ions. d. An acidic pH indicates that H + ions outnumber OH – ions. 19. The following questions relate to buffers: How do living things prevent drastic changes in pH? a. __________________________________________________________________________________________________________ _______________________________________________________________________________________________ b. Complete the following reaction, showing how the carbonic acid buffer system deals with increasing hydrogen ions in the blood: H + + HCO 3 – → ______________ c. Complete the following reaction, showing how the carbonic acid buffer system deals with decreasing hydrogen ions in the blood: H 2 CO 3 → ______________ K E Y WO R D C RO S S WO R D Review key terms by completing this crossword puzzle, using the following alphabetized list of terms: 1 2 5 3 4 6 7 acid atom base buffer compound covalent bond electron hydrogen bond ionic bond isotope molecule 8 9 10 Across 2 chemical bond in which the atoms share one pair of electrons (two words) 7 atoms having the same atomic number but a different atomic weight due to the number of neutrons 8 molecule that contains atoms of more than one element 9 substance or group of substances that tend to resist pH changes in a solution, thus stabilizing the solution’s relative acidity 10 weak bond that arises between a slightly positive hydrogen and a slightly negative oxygen, often on different molecules or separated by some distance (two words) 12 Down 1 group of atoms bonded together 3 substance tends to raise the hydrogen ion concentration in a solution and to lower its pH numerically 4 negative subatomic particle, moving about in energy levels around the nucleus of the atom 5 smallest particle of an element that displays its properties 6 substance that tends to lower the hydrogen ion concentration in a solution and to raise its pH numerically 7 chemical bond in which ions attract one another by opposite charges (two words) mad17743_ch02.qxd 3/10/06 1:48 PM Page 13 CHAPTER TEST OBJECTIVE QUESTIONS Do not refer to the text when taking this test. 1. An element has an atomic number of 11 and an atomic weight of 23. The number of neutrons in each atom is a. 11. b. 12. c. 23. d. 24. 2. The atom of an element has one proton and two neutrons. Its atomic number is a. 1. b. 2. c. 3. d. 6. 3. The atom of an element has six protons and eight neutrons. The number of electrons in this atom if neutral is a. 6. b. 8. c. 12. d. 14. 4. The relationship between 126 C and 146 C is that they are a. molecules. b. isomers. c. isotopes. d. polymers. 5. An atom has 11 protons and 12 neutrons. Its atomic mass is a. 1. b. 11. c. 12. d. 23. 6. The energy possessed by electrons in the first shell is ______________ than the energy possessed by electrons in the second shell. a. greater b. less 7. An element has an atomic number of 14. Its electron distribution over several energy shells is a. 1–4–8. b. 1–8–5. c. 2–8–2. d. 2–8–4. 8. An element has an atomic number of 13. The number of electrons in each atom’s second shell is a. 1. b. 2. c. 4. d. 8. 9. Select the reactive element by its atomic number. a. 2 b. 10 c. 12 d. 18 10. Select the most stable element by its atomic number. a. 1 b. 8 c. 10 d. 16 11. When sodium interacts with chlorine, sodium loses an electron while chlorine gains one. This interaction forms a. an ionic bond. b. a condensation synthesis. c. a condensation. d. a covalent bond. 12. Select the incorrect association. a. covalent bond—electrons transferred b. hydrogen bond—between water molecules c. ionic bond—charged particles formed d. polar covalent bond—present in the water molecule 13. Each is a property of water EXCEPT a. easily changed from liquid to gas. b. good solvent. c. maximum density at 4°C. d. molecules are cohesive. 14. Select the correct statement about acids. a. They cannot be buffered in a solution. b. They donate hydroxide ions in solution. c. HCl is an example. d. They tend to raise the pH. 15. Select the most basic pH of the given hydrogen ion concentrations. a. 1 × 10 –3 b. 1 × 10 –4 c. 1 × 10 –9 d. 1 × 10 –12 16. Select the incorrect statement about bases. a. They can be buffered in solution. b. They release hydroxide ions in solution. c. NaOH is an example. d. They tend to lower the pH. 13 mad17743_ch02.qxd 3/10/06 1:48 PM Page 14 CRITICAL THINKING QUESTIONS The introduction to this chapter is about radioactive atoms. 17. How do you know an isotope is radioactive? ________________________________________________________________ 18. How do isotopes differ from one another? ___________________________________________________________________ 19. Do isotopes have a different atomic number? ________________________________________________________________ 20. Do isotopes have a different atomic mass? __________________________________________________________________ 21. Do isotopes occupy a different position in the periodic table? ________________________________________________ 22. What does the number of an atom (element) in the periodic table tell you? ___________________________________ Test Results: ______ number correct ÷ 22 = ______ × 100 = ______ % EXPLORING THE INTERNET ARIS, the Essentials of Biology website: http://www.mhhe.com/maderessentials ARIS, the website for Essentials of Biology, offers access to a wide variety of tools to help students learn biological concepts and to reinforce their knowledge. Online study aids such as practice quizzes, interactive activities, animations, labeling exercises, flashcards, and much more are organized according to the major sections of each chapter. There is even an online tutorial service! ANSWER KEY CHAPTER KEY TERMS a. acid b. hydrophilic c. hydrophobic d. atom e. base f. electron g. proton h. ion i. polar j. buffer k. covalent bond l. octet rule m. pH scale 7. a. T b. T c. T d. F 8. a. two b. seven 9. a.S b. Ne c. S has six electrons in its outer shell, and if it reacts to gain two more it will have a stable outer configuration of eight; Ne already has a stable outer shell. STUDY EXERCISES 1. carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur 2. a. 9 b. 18 c. 9 3. a. periods b. groups c. noble gases d. rarely 4. a. number b. neutrons 5. a. isotopes b. atomic mass c. 8 d. 8 e. 8 f. 10 g. 168 O has eight neutrons and 188 O has ten neutrons in the nucleus. 6. 14 Protons Neutrons Atomic Number Atomic Mass 6 6 6 12 6 8 6 14 15 16 15 31 15 18 15 33 mad17743_ch02.qxd 3/10/06 1:48 PM Page 15 17. 10. pH 12 P 12 N Acid/Base/Neutral 7 neutral 3 acid 8 base 18. a. F b. T c. T d. T 19. a. The pH is stabilized through the action of buffers, chemicals or combinations of chemicals that take up excess H + or OH – to keep the pH steady. b. H 2 CO 3 c. HCO 3 – + H + KEYWORD CROSSWORD 11. a. two b. seven c. one, two d. Cl e. –1 f. Ca g. +2 h. ionic i. CaCl 2 12. 1 5 M A 2 C 3 O V L 4 A L 6 N T B L O A M S E C E I E C D C U O N D O N E T L R 7 I E S O O T O P E N N N I 8 C O M P O U U F F E R R O G E N D 9 B O N 10 H Y D B D CHAPTER TEST 13. a. I b. C c. I d. C e. H 14. b, d, e, g 15. a. The partial charges of the water molecule attract and disperse charged particles in solution. b. It takes up and releases large amounts of heat without much change in temperature. c. Water is most dense at 4°C. It expands as the temperature drops from this point; it is less dense at 0°C, the temperature of ice. 16. a. B b. A c. B d. A e. A f. B 1. b 2. a 3. a 4. c 10. c 11. a 12. a 17. gives off subatomic trons 19. no 20. yes 5. d 6. b 7. d 8. d 9. c 13. a 14. c 15. d 16. d particles 18. number of neu21. no 22. number of protons 15