1. : Chemical Bonds

2. 2.5 Chemical Properties of Atoms
Electrons are directly involved in the chemical activity of an atom.
Electrons can be located in different electron shells, each with a different distance from the nucleus.
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
First
shell
Third
Sodium
Magnesium
Aluminum
Silicon
Phosphorus
Sulfur
Chlorine
Argon
Active Lecture Tips
 Ask students to use 3 to 4 minutes to turn to someone near them to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Nearby pairs might provide immediate critiques with each other before passing along analogies for the entire class to consider. After these discussions, have pairs of students share their analogies with the entire class. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and critical thinking skills. For example, ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both men look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.)
• See the essay Relating Chemical Bonds to Everyday Ideas on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.
Second
shell 2

3. Valence Electrons
The number of electrons in the outermost shell, called the valence shell, determines the chemical properties of the atom.
Atoms whose outer shells are not full tend to interact with other atoms to complete or fill their valence shells.
Each atom will share, donate, or receive electrons, so that both partners end up with completed outer shells.
These interactions result in chemical bonds.
Active Lecture Tips
 Ask students to use 3 to 4 minutes to turn to someone near them to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Nearby pairs might provide immediate critiques with each other before passing along analogies for the entire class to consider. After these discussions, have pairs of students share their analogies with the entire class. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and critical thinking skills. For example, ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both men look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.)
• See the essay Relating Chemical Bonds to Everyday Ideas on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3

4. Sodium chloride (NaCl)
2.7 Ionic bonds
An ion is an atom or molecule with an electrical charge resulting from gain or loss of one or more electrons.
Two ions with opposite charges (+ and -) attract each other creating an ionic bond.
Na Sodium atom
Cl Chlorine atom
Na+ Sodium ion
Cl− Chloride ion
Na+ Na
Cl− Cl +
Sodium chloride (NaCl)
Active Lecture Tips
 Ask students to use 3 to 4 minutes to turn to someone near them to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Nearby pairs might provide immediate critiques with each other before passing along analogies for the entire class to consider. After these discussions, have pairs of students share their analogies with the entire class. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and critical thinking skills. For example, ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both men look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.)
• See the essay Relating Chemical Bonds to Everyday Ideas on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4

5. 2.6 Covalent Bonds
In a covalent bond, two atoms, each with an unpaired electron in its outer shell, actually share a pair of electrons.
Two or more atoms held together by covalent bonds form a molecule.
Student Misconceptions and Concerns
• Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.6 and the differences and limitations of representing atomic structure. The contrast in Figure 2.6 is a good beginning for such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as discussed in Module 2.3.
Teaching Tips
• Have your students try to calculate the number of covalent bonds possible for a variety of atoms. (Carbon, for example, can form up to four covalent bonds.) Then provide the students with a list of elements and the number of outer electrons for each and have them make predictions about the chemical formula for many types of molecules. (For example, carbon could form covalent bonds with four hydrogen atoms.)
• Modules 2.6 and 2.8 discuss the special bonding in and between water molecules. Many students do not appreciate the importance of weak chemical bonds in water and cellular chemistry. Extra time and attention may be required to address this special aspect of chemistry.
Active Lecture Tips
 Ask students to use 3 to 4 minutes to turn to someone near them to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Nearby pairs might provide immediate critiques with each other before passing along analogies for the entire class to consider. After these discussions, have pairs of students share their analogies with the entire class. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and critical thinking skills. For example, ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both men look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.)
• See the essay Relating Chemical Bonds to Everyday Ideas on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5

6. 2.7 Electronegativity and Polarity
Atoms in a covalently bonded molecule continually compete for shared electrons.
The attraction (pull) for shared electrons is called electronegativity.
In molecules of only one element, the pull toward each atom is equal, because each atom has the same electronegativity and are called nonpolar covalent bonds.
Student Misconceptions and Concerns
• Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.6 and the differences and limitations of representing atomic structure. The contrast in Figure 2.6 is a good beginning for such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as discussed in Module 2.3.
Teaching Tips
• Have your students try to calculate the number of covalent bonds possible for a variety of atoms. (Carbon, for example, can form up to four covalent bonds.) Then provide the students with a list of elements and the number of outer electrons for each and have them make predictions about the chemical formula for many types of molecules. (For example, carbon could form covalent bonds with four hydrogen atoms.)
• Modules 2.6 and 2.8 discuss the special bonding in and between water molecules. Many students do not appreciate the importance of weak chemical bonds in water and cellular chemistry. Extra time and attention may be required to address this special aspect of chemistry.
Active Lecture Tips
 Ask students to use 3 to 4 minutes to turn to someone near them to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Nearby pairs might provide immediate critiques with each other before passing along analogies for the entire class to consider. After these discussions, have pairs of students share their analogies with the entire class. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and critical thinking skills. For example, ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both men look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.)
• See the essay Relating Chemical Bonds to Everyday Ideas on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 6

7. Electronegativity and Polarity
Water has atoms with different electronegativities.
Oxygen attracts the shared electrons more strongly than hydrogen.
The oxygen atom has a slightly negative charge and the hydrogen atoms have a slightly positive charge resulting in a polar covalent bond.
Polar covalent bonds
in a water molecule
(slightly +) O H
(slightly −)
Student Misconceptions and Concerns
• Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.6 and the differences and limitations of representing atomic structure. The contrast in Figure 2.6 is a good beginning for such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as discussed in Module 2.3.
Teaching Tips
• Have your students try to calculate the number of covalent bonds possible for a variety of atoms. (Carbon, for example, can form up to four covalent bonds.) Then provide the students with a list of elements and the number of outer electrons for each and have them make predictions about the chemical formula for many types of molecules. (For example, carbon could form covalent bonds with four hydrogen atoms.)
• Modules 2.6 and 2.8 discuss the special bonding in and between water molecules. Many students do not appreciate the importance of weak chemical bonds in water and cellular chemistry. Extra time and attention may be required to address this special aspect of chemistry.
Active Lecture Tips
 Ask students to use 3 to 4 minutes to turn to someone near them to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Nearby pairs might provide immediate critiques with each other before passing along analogies for the entire class to consider. After these discussions, have pairs of students share their analogies with the entire class. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and critical thinking skills. For example, ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both men look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.)
• See the essay Relating Chemical Bonds to Everyday Ideas on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 7

8. 2.7 Electronegativity and Polarity

9. 2.8 Hydrogen bonds
(−)
(+)
Hydrogen bond
Polar covalent bonds
Hydrogen bonds are weak bonds important in the chemistry of life.
Hydrogen bonds form between water molecules.
Each positive H atom in water can form a bond with a partially negative O atom of another water molecule.
Teaching Tips
• Modules 2.6 and 2.8 discuss the special bonding in and between water molecules. Many students do not appreciate the importance of weak chemical bonds in water and cellular chemistry. Extra time and attention may be required to address this special aspect of chemistry.
Active Lecture Tips
 Ask students to use 3 to 4 minutes to turn to someone near them to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Nearby pairs might provide immediate critiques with each other before passing along analogies for the entire class to consider. After these discussions, have pairs of students share their analogies with the entire class. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and critical thinking skills. For example, ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both men look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.)
• See the essay Relating Chemical Bonds to Everyday Ideas on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 9

10. 2.9 Chemical reactions make and break chemical bonds
Chemical reactions do not create or destroy matter.
Chemical reactions only rearrange matter.
Remember that the structure of atoms and molecules determines the way they behave in a chemical reaction.
Student Misconceptions and Concerns
• Students may misunderstand the chemical shorthand equation of photosynthesis presented in Module 2.9. As noted in the text, this overall equation does not include many smaller steps and reactions that occur in photosynthesis. If you discuss additional details of photosynthesis in your course, you might mention that you will add more to this equation at a later time.
• A common student misconception is that energy is produced by a chemical reaction. When introducing chemical reactions, consider addressing the conservation of energy (the first law of thermodynamics) and the investment and release of energy in the creation and breaking of chemical bonds.
Teaching Tips
• As noted in the text, chemical reactions do not create or destroy matter. Instead, they rearrange the structure and form new relationships. This is much like shuffling and dealing cards. When playing poker, cards are neither created nor destroyed. Instead, new combinations are formed as the cards are dealt to the players.
• The overall reaction of photosynthesis illustrates the investment and release of energy by chemical reactions. Consider discussing the investment of sunlight energy to create chemical bonds and the release of energy in the form of heat when plant materials are burned. (Animals invest some of the energy released by the breakdown of sugars to form new chemical bonds, such as those in ATP.)
Active Lecture Tips
 Ask students to use 3 to 4 minutes to turn to someone near them to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Nearby pairs might provide immediate critiques with each other before passing along analogies for the entire class to consider. After these discussions, have pairs of students share their analogies with the entire class. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and critical thinking skills. For example, ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both men look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.)
• See the essay Relating Chemical Bonds to Everyday Ideas on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 10