PITTS' BIOLOGY 110 CHEMISTRY REVIEW PART ONE
1. What is an atom?
2. What is a molecule?
3. What is an element?
4. What is a compound?
5. What is the chemical symbol for oxygen?
6. What is the chemical symbol for sodium?
7. What is the chemical symbol for nitrogen?
8. What is the chemical symbol for potassium?
9. What is the chemical symbol for chlorine?
10. What is the chemical symbol for carbon?
11. How many atoms are present in one molecule of water (H2O) ?
12. How many atoms are present in one molecule of glucose (C6H12O6) ?
13. How many molecules of carbon dioxide are indicated by : 8CO2 ?
14. How many atoms are present in 8CaCl2 ?
15. What type of electrical charge is present on a proton?
16. In what part of an atom are protons located?
17. Define: atomic number (AN)
18. What is the atomic number of carbon? hydrogen? oxygen?
19. If a carbon atom gains a proton, will the atom still have the properties of carbon?
20. True or False Each oxygen atom has 8 protons.
21. What is the electrical charge on an electron?
22. In what part of an atom are electrons located?
23. How many electrons are present in an atom?
24. Define: mass number (= atomic weight, AW)
25. Helium (He) has 2 protons and 2 neutrons; what is the (a) atomic number and (b) the mass number of helium?
26. Fluorine (F) has an atomic number of 9 and contains 10 neutrons in each atom. (a) What is the mass number of fluorine? (b) How many protons are present in one atom of fluorine? (c) How many electrons are present in one atom of fluorine before it reacts with other atoms?
27. Sulfur (S) has an atomic number of 16 and a mass number of 32. How many protons, neutrons, and electrons are present in one atom?
28. An atom of aluminum (Al) contains 13 protons and has a mass number of 27; how many protons, neutrons, and electrons are present in one atom?
29. True or False All electrons contain the same amount of energy.
30. How many electrons can the first (i.e., the inner) shell of an atom hold?
31. How many electrons can the second shell of an atom hold?
32. How many electrons can the outer shell of an atom hold?
33. Which shell has electrons with the lowest amount of energy?
34. Which shell has electrons with the highest amount of energy?
35. What happens to the energy level of an electron as it moves from the second shell to the third shell?
36. What happens to the energy level of an electron as it moves from the fourth shell to the third shell?
37. How many electrons and protons are present in an atom that is electrically neutral?
38. How does an atom become stable?
39. Which will an atom attempt to do: become neutral or become stable ?
40. Chlorine (Cl) has an atomic number of 17. How many protons does it possess? How many electrons does it possess? How many electrons are present in its first shell? in its second shell? in its third shell?
41. Is chlorine stable when it has 17 electrons? if not, explain why.
42. Define: ion
43. Sodium (Na) has an atomic number of 11. How many protons does it possess? How many electrons does it possess? How many electrons are in its first shell? in its second shell? in its third shell?
44. Is sodium (Na) stable with 11 electrons? If not, explain why.
45. Name an example of an ion with a negative charge on it. Explain why it has a negative charge.
46. Name an example of an ion with a positive charge on it. Explain why it has a positive charge.
47. What happens when two ions with the same type of charge (i.e., both ions are either positive or negative) come near each other?
48. What happens when two ions with opposite charges (i.e., one is negative and one is positive) come near each other?
49. Define: ionic bond
50. Why is an oxygen atom with 8 electrons not stable?
51. How can an oxygen atom with 8 electrons become stable?
52. Why is a hydrogen atom with 1 electron not stable?
53. How can a hydrogen atom with 1 electron become stable?
54. Explain how one atom of oxygen and two atoms of hydrogen can bond with each other and result in all three atoms becoming stable.
55. Define: covalent bonding
56. Explain why ammonia (NH3) is stable (N has an atomic number = 7)
57. Why is NH4 not stable?
58. In a water molecule, are the electrons shared evenly between the oxygen and hydrogen atoms? Explain your answer.
59. Define: polarized molecule
60. Name an example of a molecule that is covalently bonded but is not polarized. Why is this molecule not polarized?
61. Is a water molecule polarized? Why?
62. How do two water molecules react with each other when they are close together?
63. Define: hydrogen bond
64. Name an example of two molecules that are held together by hydrogen bonding.
65. Define: cohesion
66. Define: adhesion
67. Considering the energy levels of the reactants and the energy levels of the products of reactions, name two types of chemical reactions.
68. Define: catalyst
69. After the completion of a chemical reaction involving a catalyst, how much of the catalyst remains?
70. Define: enzyme
71. True or False All catalysts are enzymes.
72. True or False All enzymes are catalysts.
73. True or False All enzymes are composed of proteins.
74. True or False Proteins are used only as enzymes.
75. What three letters are present at the end of the name of most enzymes?
ANSWERS
1. An atom is the smallest part of an element that still retains the properties of that element. If we break the atom apart, the parts will no longer have the properties of that element. An atom consists of several subatomic particles, three of which (proton, neutron, and electron) are discussed in General Biology.
2. A molecule is a particle formed by the chemical bonding of two or more atoms. A molecule is the smallest unit of a compound that has the properties of that compound.
3. An element is a substance that is composed of one kind of atom; examples include carbon, oxygen, hydrogen.
4. A compound contains atoms of two or more elements chemically bonded in a specific ratio. Examples include H2O, CO2, and NaCl.
5. O
6. Na
7. N
8. K
9. Cl
10. C
11. One molecule of water contains a total of 3 atoms: 2 atoms of hydrogen and 1 atom of oxygen. (Reminder: if a molecular formula has an element with no subscript after it, this means that only one atom of that element is present in the molecule. The formula for water could be (but is not!) written H201.)
12. One molecule of glucose contains 24 atoms: 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen.
13. The 8 in front of CO2 indicates that 8 molecules of carbon dioxide are present. The 8 does not simply mean that 8 carbon atoms are present; instead, the 8 means that 8 carbon atoms and 8 X 2 (=16) oxygen atoms are present.
14. Eight molecules of CaCl2 contain 8 calcium atoms plus 8 X 2 (=16) chlorine atoms for a total of 24 atoms.
15. A proton has a positive charge.
16. Protons are located in the nucleus of an atom.
17. The atomic number of an atom is equal to the number of protons present.
18. The atomic number of carbon is 6 (i.e., each carbon atom contains 6 protons), the atomic number of hydrogen = 1, and the atomic number of oxygen = 8.
19. If a carbon atom gains a proton the nucleus will now have 7 protons and will no longer be carbon but instead will be nitrogen which has an atomic number of 7.
20. True; since the atomic number of oxygen is 8, each oxygen atom will contain exactly 8 protons.
21. Each electron has a negative charge.
22. Electrons are located in shells or layers (actually, energy levels) around the nucleus of the atom.
23. The number of electrons in an atom depends on several factors. Before an atom reacts with other atoms, the number of electrons present is usually equal to the number of protons. During a reaction, however, the atom may gain or lose electrons depending on the original number of electrons in its outer shell.
24. The mass number (a more recent term that has replaced the older term “atomic weight”) is equal to the number of protons plus the number of neutrons. For practical purposes (at least in General Biology) the mass of the electrons can be ignored since the electrons are so small.
25. The atomic number of helium is 2 (2 protons) and the mass number is 4 (2 protons plus 2 neutrons).
26. The mass number of fluorine is 19. One atom of fluorine contains 9 protons and 9 electrons.
27. One atom of sulfur contains 16 protons, 16 electrons, and 16 neutrons.
28. One atom of aluminum contains 13 protons, 13 electrons, and 14 neutrons.
29. False (Reminder: while all electrons are small and all of the electrons we consider in General Biology have negative charges, they differ in the amount of energy they possess.)
30. The first shell of an atom can hold 2 electrons. This does not mean that all atoms do have 2 electrons in their first shell. The exception is hydrogen (atomic number = 1) which has only 1 electron in its first shell before reacting with other atoms.
31. The second shell of an atom can hold a maximum of 8 electrons. Many atoms, such as carbon (atomic number =6), have the second shell only partially filled before reacting with other atoms.
32. If the outer shell is the first shell, it is filled with 2 electrons. All other outer shells are filled with 8 electrons.
33. The first shell (i.e., the innermost shell) has electrons with the lowest energy levels.
34. The further an electron is from the nucleus of an atom, the higher the energy level; therefore, the outer shell will have electrons with the highest energy levels.
35. If an electron moves from the second shell to the third shell (i.e., away from the nucleus of the atom), the electron will have to gain energy.
36. If an electron moves from the fourth shell to the third shell (i.e., toward the nucleus of the atom), the electron will have to release energy.
37. An electrically neutral atom is an atom in which the number of protons (which have positive charges) and the number of electrons (which have negative charges) are equal. For example, an oxygen atom with 8 protons and 8 electrons is neutral.
38. An atom that is stable has its outer shell, whatever that shell number may be, filled with electrons.
39. Become stable. Any atom with its outer shell not filled with electrons will attempt to become stable by filling its outer shell. This may involve either gaining electrons or losing electrons.
40. An atom of chlorine contains 17 protons and, before reacting, 17 electrons. The first electron shell contains 2 electrons, the second shell contains 8 electrons, and the third shell contains 7 electrons.
41. Chlorine is not stable when it has 17 electrons because the outer shell, with 7 electrons, is not filled.
42. An ion is a charged atom that has an unequal number of protons and electrons. An ion may be either negatively charged or positively charged depending on whether electrons or protons are more abundant.
43. A sodium atom has 11 protons and 11 electrons. The first shell contains 2 electrons, the second shell contains 8 electrons, and the third shell contains 1 electron.
44. Sodium is not stable with 11 electrons because the outer shell, with 1 electron, is not full.
45. Chlorine (atomic number = 17) has 7 electrons in its outer shell before it reacts with other atoms. As a result of chemical reaction, the chlorine atom gains 1 electron which fills the outer shell (with 8 electrons) and brings the total number of electrons in the atom to 18. Since chlorine has 17 protons and now has 18 electrons, it is a negative ion (Cl-).
46. Sodium (atomic number = 11) has 1 electron in its outer shell before reacting; this electron is lost during chemical reactions resulting in the atom having 11 protons and 10 electrons; it is now a positive ion (Na+).
47. Two ions with like charges (i.e., positive and positive) will repel each other.
48. Two ions with opposite charges (positive and negative) will attract each other.
49. An ionic bond results from the attraction between two oppositely charged ions; for example, Na+ and Cl- will attract each other and form the compound NaCl (table salt).
50. An oxygen atom with 8 electrons is not stable because the outer shell (which is in this case the second shell) contains 6 electrons.
51. An oxygen atom with 6 electrons in its outer shell can become stable by gaining 2 electrons and filling its outer shell.
52. A hydrogen atom with 1 electron is not stable because the first shell is not full of electrons.
53. A hydrogen atom with 1 electron can become stable by gaining 1 electron.
54. One oxygen atom can borrow an electron from each of two hydrogen atoms and become stable. In a like manner, each hydrogen atom can borrow one electron from the oxygen atom and become stable. In this manner the oxygen atom can have, in effect, 8 electrons in its outer shell and each of the hydrogen atoms can have, in effect, 2 electrons in their outer shell. As a result of this sharing, all of the atoms are stable.
55. Covalent bonding results from the sharing (not transfer) of electrons between two atoms.
56. Ammonia is stable (but can be caused to react and become more stable) because nitrogen, which has 5 electrons in its outer shell before reacting, borrows an electron from each of three hydrogen atoms and becomes stable. Likewise, each of the three hydrogen atoms becomes stable by borrowing an electron from nitrogen and filling the first (and outer) shell of hydrogen with 2 electrons. Three covalent bonds are formed as the one nitrogen and three hydrogen atoms react.
57. NH4 is not stable because the electron of the fourth hydrogen atom will not fit into the already filled outer shell of nitrogen. In this situation, the molecule releases the “extra” electron and becomes positively charged (NH4+).
58. In a water molecule the electrons are not shared evenly in the covalent bonds between the oxygen atom and the two hydrogen atoms because the 8 protons in oxygen have a stronger attraction for the negatively charged electrons than do the single protons in each of the hydrogen atoms.
59. A polarized molecule is a covalently bonded molecule in which the electrons are not shared equally. This results in part of the molecule being positively charged and other areas being negatively charged.
60. A hydrogen molecule (H2) is covalently bonded but it is not polarized since there are equal numbers of protons in each atom. Therefore, the electrons will be shared equally.
61. A water molecule is polarized because oxygen has a stronger attraction for the shared electrons than do the hydrogen atoms.
62. Two water molecules will attract each other because the negative charge on the oxygen atom of one water molecule will be pulled toward the positive charge on one of the hydrogen atoms in another water molecule.
63. Hydrogen bonding results from the attraction between two polarized molecules.
64. A water molecule is “held” to three other water molecules by hydrogen bonding.
65. Cohesion is the attraction between two or more polarized molecules of the same substance.
66. Adhesion is the attraction between two or more polarized molecules that are not alike.
67. Considering energy levels, chemical reactions may be divided into two categories: (a) energy requiring, and (b) energy releasing.
68. A catalyst is a substance that affects the rate of a chemical reaction but is not consumed during the reaction.
69. The amount of a catalyst present at the end of a reaction should be same as was present at the beginning of the reaction.
70. An enzyme is a catalyst composed of protein.
71. False. Many catalysts, such as platinum, are not composed of protein.
72. True
73. True
74. False. Proteins have many uses in cells, such as being used as a structural material to build cell parts.
75. Most, but not all, enzyme names end in the three letters “-ase.”