Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Figure 2.1 Abbreviated periodic table of the elements.

Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Figure 2.4 Two simplified models of a helium atom.

Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Figure 2.5 Atoms of the four elements most abundant in living matter.

Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Figure 2.UN7 Summary: Electron sharing

Figure 2.7 Alternate ways to represent molecules.

Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Figure 2.UN2 Water molecule polarity

Student Misconceptions and Concerns 1. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. 2. Students with limited backgrounds in chemistry will benefit from a discussion of Figure 2.5 and the differences and limitations of diagrams of atomic structure. The contrast in Figure 2.5 is a good beginning of such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as indicated in the Figure 2.5 legend. 3. The dangers posed by certain chemicals in our food and broader environment often misleads people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean food. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes towards chemicals. 4. The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of the species. A zoo might have trouble keeping a particular animal because science has not fully determined what trace elements the animal requires. 2. Many breakfast cereals are fortified with iron. A person can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imagining device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example. 3. Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton is as massive as a bowling ball, an electron will be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the textbook’s formula that an electron is 1/2,000 the mass of a proton.) 4. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. 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. 5. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds discussed. Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships. Small groups might provide immediate critiques before passing along analogies for the entire class to consider.

Student Misconceptions and Concerns 1. Students are unlikely to have carefully considered the four special properties of water that are apparent in our lives. However, these properties are of great biological significance and are often familiar parts of our lives. The connections between these properties and personal experiences can invest great meaning into a discussion of water’s properties. A homework assignment asking for three examples of each of these properties in each student’s experiences will require reflection and potentially produce meaningful illustrations. Similarly, quizzes or exam questions matching examples of each property to a list of the properties requires high-level evaluative analysis. 2. Students at all levels struggle with the distinction between heat and temperature. Students might also expect that all ice is about the same temperature, 0˚C. Redefining and correcting misunderstandings often takes more class time and energy than introducing previously unknown concepts. Teaching Tips 1. Here is a way to have your students think about the sticky nature of water in their lives. Ask them to consider the need for a towel after a shower or a bath. Once we get out of the shower or bath, we have left the source of water. So why do we need the towel? The reason we need a towel to dry off is that water is still clinging to our bodies because water molecules are polar. The molecules on cell surfaces are also polar, so our skin and the water both stick to each other. 2. Some students may be intrigued if you tell them that you too can stand on the surface of water—when it is frozen. Thus, it is necessary to note a liquid water surface when talking about surface tension. 3. Have students compare the seasonal ranges of temperatures of Anchorage and Fairbanks, Alaska. (Many websites, such as Yahoo, provide weather information about various cities.) These two northern cities have large differences in their annual temperature ranges. Make the point that the coastal location of Anchorage moderates the temperature. 4. Several versions of the following analogy are easy to relate to students. (a) Ask students how the average on an exam would be affected if the brightest students didn’t take the test. (b) The authors note that the performance of a track team would drop if the fastest sprinters didn’t compete. In both analogies, removing the top performers lowers the average just as the evaporation of the most active water molecules cools the evaporative surface. 5. It is not the heat, it is the humidity. The efficiency of evaporative cooling is affected by humidity. As humidity rises, the rate of evaporation decreases, making it more difficult to cool our heat-generating bodies on a warm and humid summer day. 6. Ask your students if the ocean levels would change if ice didn’t float. They can try this experiment to find out. Place several large chunks of ice in a glass and fill the glass up completely with water to the top rim. Thus, the ice cubes should be sticking up above the top of the filled glass. Will the glass overflow when the ice melts? (No.) This phenomenon is important when we consider the potential consequences of global warming. If floating glaciers melt, ocean levels will not be affected. However, if the ice over land melts, we can expect increased ocean levels. 7. The Environmental Protection Agency (EPA) website (www.epa.gov/acidrain/education/) includes good information about acid precipitation and teaching ideas. 8. The SETI (Search For Extraterrestrial Intelligence) Institute’s Mission is to explore, understand and explain the origin, nature, and prevalence of life in the universe (www.seti.org). Your students might enjoy exploring this respected scientific organization.

Student Misconceptions and Concerns 1. Students are unlikely to have carefully considered the four special properties of water that are apparent in our lives. However, these properties are of great biological significance and are often familiar parts of our lives. The connections between these properties and personal experiences can invest great meaning into a discussion of water’s properties. A homework assignment asking for three examples of each of these properties in each student’s experiences will require reflection and potentially produce meaningful illustrations. Similarly, quizzes or exam questions matching examples of each property to a list of the properties requires high-level evaluative analysis. 2. Students at all levels struggle with the distinction between heat and temperature. Students might also expect that all ice is about the same temperature, 0˚C. Redefining and correcting misunderstandings often takes more class time and energy than introducing previously unknown concepts. Teaching Tips 1. Here is a way to have your students think about the sticky nature of water in their lives. Ask them to consider the need for a towel after a shower or a bath. Once we get out of the shower or bath, we have left the source of water. So why do we need the towel? The reason we need a towel to dry off is that water is still clinging to our bodies because water molecules are polar. The molecules on cell surfaces are also polar, so our skin and the water both stick to each other. 2. Some students may be intrigued if you tell them that you too can stand on the surface of water—when it is frozen. Thus, it is necessary to note a liquid water surface when talking about surface tension. 3. Have students compare the seasonal ranges of temperatures of Anchorage and Fairbanks, Alaska. (Many websites, such as Yahoo, provide weather information about various cities.) These two northern cities have large differences in their annual temperature ranges. Make the point that the coastal location of Anchorage moderates the temperature. 4. Several versions of the following analogy are easy to relate to students. (a) Ask students how the average on an exam would be affected if the brightest students didn’t take the test. (b) The authors note that the performance of a track team would drop if the fastest sprinters didn’t compete. In both analogies, removing the top performers lowers the average just as the evaporation of the most active water molecules cools the evaporative surface. 5. It is not the heat, it is the humidity. The efficiency of evaporative cooling is affected by humidity. As humidity rises, the rate of evaporation decreases, making it more difficult to cool our heat-generating bodies on a warm and humid summer day. 6. Ask your students if the ocean levels would change if ice didn’t float. They can try this experiment to find out. Place several large chunks of ice in a glass and fill the glass up completely with water to the top rim. Thus, the ice cubes should be sticking up above the top of the filled glass. Will the glass overflow when the ice melts? (No.) This phenomenon is important when we consider the potential consequences of global warming. If floating glaciers melt, ocean levels will not be affected. However, if the ice over land melts, we can expect increased ocean levels. 7. The Environmental Protection Agency (EPA) website (www.epa.gov/acidrain/education/) includes good information about acid precipitation and teaching ideas. 8. The SETI (Search For Extraterrestrial Intelligence) Institute’s Mission is to explore, understand and explain the origin, nature, and prevalence of life in the universe (www.seti.org). Your students might enjoy exploring this respected scientific organization.

Student Misconceptions and Concerns 1. Students are unlikely to have carefully considered the four special properties of water that are apparent in our lives. However, these properties are of great biological significance and are often familiar parts of our lives. The connections between these properties and personal experiences can invest great meaning into a discussion of water’s properties. A homework assignment asking for three examples of each of these properties in each student’s experiences will require reflection and potentially produce meaningful illustrations. Similarly, quizzes or exam questions matching examples of each property to a list of the properties requires high-level evaluative analysis. 2. Students at all levels struggle with the distinction between heat and temperature. Students might also expect that all ice is about the same temperature, 0˚C. Redefining and correcting misunderstandings often takes more class time and energy than introducing previously unknown concepts. Teaching Tips 1. Here is a way to have your students think about the sticky nature of water in their lives. Ask them to consider the need for a towel after a shower or a bath. Once we get out of the shower or bath, we have left the source of water. So why do we need the towel? The reason we need a towel to dry off is that water is still clinging to our bodies because water molecules are polar. The molecules on cell surfaces are also polar, so our skin and the water both stick to each other. 2. Some students may be intrigued if you tell them that you too can stand on the surface of water—when it is frozen. Thus, it is necessary to note a liquid water surface when talking about surface tension. 3. Have students compare the seasonal ranges of temperatures of Anchorage and Fairbanks, Alaska. (Many websites, such as Yahoo, provide weather information about various cities.) These two northern cities have large differences in their annual temperature ranges. Make the point that the coastal location of Anchorage moderates the temperature. 4. Several versions of the following analogy are easy to relate to students. (a) Ask students how the average on an exam would be affected if the brightest students didn’t take the test. (b) The authors note that the performance of a track team would drop if the fastest sprinters didn’t compete. In both analogies, removing the top performers lowers the average just as the evaporation of the most active water molecules cools the evaporative surface. 5. It is not the heat, it is the humidity. The efficiency of evaporative cooling is affected by humidity. As humidity rises, the rate of evaporation decreases, making it more difficult to cool our heat-generating bodies on a warm and humid summer day. 6. Ask your students if the ocean levels would change if ice didn’t float. They can try this experiment to find out. Place several large chunks of ice in a glass and fill the glass up completely with water to the top rim. Thus, the ice cubes should be sticking up above the top of the filled glass. Will the glass overflow when the ice melts? (No.) This phenomenon is important when we consider the potential consequences of global warming. If floating glaciers melt, ocean levels will not be affected. However, if the ice over land melts, we can expect increased ocean levels. 7. The Environmental Protection Agency (EPA) website (www.epa.gov/acidrain/education/) includes good information about acid precipitation and teaching ideas. 8. The SETI (Search For Extraterrestrial Intelligence) Institute’s Mission is to explore, understand and explain the origin, nature, and prevalence of life in the universe (www.seti.org). Your students might enjoy exploring this respected scientific organization.

Student Misconceptions and Concerns 1. Students are unlikely to have carefully considered the four special properties of water that are apparent in our lives. However, these properties are of great biological significance and are often familiar parts of our lives. The connections between these properties and personal experiences can invest great meaning into a discussion of water’s properties. A homework assignment asking for three examples of each of these properties in each student’s experiences will require reflection and potentially produce meaningful illustrations. Similarly, quizzes or exam questions matching examples of each property to a list of the properties requires high-level evaluative analysis. 2. Students at all levels struggle with the distinction between heat and temperature. Students might also expect that all ice is about the same temperature, 0˚C. Redefining and correcting misunderstandings often takes more class time and energy than introducing previously unknown concepts. Teaching Tips 1. Here is a way to have your students think about the sticky nature of water in their lives. Ask them to consider the need for a towel after a shower or a bath. Once we get out of the shower or bath, we have left the source of water. So why do we need the towel? The reason we need a towel to dry off is that water is still clinging to our bodies because water molecules are polar. The molecules on cell surfaces are also polar, so our skin and the water both stick to each other. 2. Some students may be intrigued if you tell them that you too can stand on the surface of water—when it is frozen. Thus, it is necessary to note a liquid water surface when talking about surface tension. 3. Have students compare the seasonal ranges of temperatures of Anchorage and Fairbanks, Alaska. (Many websites, such as Yahoo, provide weather information about various cities.) These two northern cities have large differences in their annual temperature ranges. Make the point that the coastal location of Anchorage moderates the temperature. 4. Several versions of the following analogy are easy to relate to students. (a) Ask students how the average on an exam would be affected if the brightest students didn’t take the test. (b) The authors note that the performance of a track team would drop if the fastest sprinters didn’t compete. In both analogies, removing the top performers lowers the average just as the evaporation of the most active water molecules cools the evaporative surface. 5. It is not the heat, it is the humidity. The efficiency of evaporative cooling is affected by humidity. As humidity rises, the rate of evaporation decreases, making it more difficult to cool our heat-generating bodies on a warm and humid summer day. 6. Ask your students if the ocean levels would change if ice didn’t float. They can try this experiment to find out. Place several large chunks of ice in a glass and fill the glass up completely with water to the top rim. Thus, the ice cubes should be sticking up above the top of the filled glass. Will the glass overflow when the ice melts? (No.) This phenomenon is important when we consider the potential consequences of global warming. If floating glaciers melt, ocean levels will not be affected. However, if the ice over land melts, we can expect increased ocean levels. 7. The Environmental Protection Agency (EPA) website (www.epa.gov/acidrain/education/) includes good information about acid precipitation and teaching ideas. 8. The SETI (Search For Extraterrestrial Intelligence) Institute’s Mission is to explore, understand and explain the origin, nature, and prevalence of life in the universe (www.seti.org). Your students might enjoy exploring this respected scientific organization.

Student Misconceptions and Concerns 1. Students are unlikely to have carefully considered the four special properties of water that are apparent in our lives. However, these properties are of great biological significance and are often familiar parts of our lives. The connections between these properties and personal experiences can invest great meaning into a discussion of water’s properties. A homework assignment asking for three examples of each of these properties in each student’s experiences will require reflection and potentially produce meaningful illustrations. Similarly, quizzes or exam questions matching examples of each property to a list of the properties requires high-level evaluative analysis. 2. Students at all levels struggle with the distinction between heat and temperature. Students might also expect that all ice is about the same temperature, 0˚C. Redefining and correcting misunderstandings often takes more class time and energy than introducing previously unknown concepts. Teaching Tips 1. Here is a way to have your students think about the sticky nature of water in their lives. Ask them to consider the need for a towel after a shower or a bath. Once we get out of the shower or bath, we have left the source of water. So why do we need the towel? The reason we need a towel to dry off is that water is still clinging to our bodies because water molecules are polar. The molecules on cell surfaces are also polar, so our skin and the water both stick to each other. 2. Some students may be intrigued if you tell them that you too can stand on the surface of water—when it is frozen. Thus, it is necessary to note a liquid water surface when talking about surface tension. 3. Have students compare the seasonal ranges of temperatures of Anchorage and Fairbanks, Alaska. (Many websites, such as Yahoo, provide weather information about various cities.) These two northern cities have large differences in their annual temperature ranges. Make the point that the coastal location of Anchorage moderates the temperature. 4. Several versions of the following analogy are easy to relate to students. (a) Ask students how the average on an exam would be affected if the brightest students didn’t take the test. (b) The authors note that the performance of a track team would drop if the fastest sprinters didn’t compete. In both analogies, removing the top performers lowers the average just as the evaporation of the most active water molecules cools the evaporative surface. 5. It is not the heat, it is the humidity. The efficiency of evaporative cooling is affected by humidity. As humidity rises, the rate of evaporation decreases, making it more difficult to cool our heat-generating bodies on a warm and humid summer day. 6. Ask your students if the ocean levels would change if ice didn’t float. They can try this experiment to find out. Place several large chunks of ice in a glass and fill the glass up completely with water to the top rim. Thus, the ice cubes should be sticking up above the top of the filled glass. Will the glass overflow when the ice melts? (No.) This phenomenon is important when we consider the potential consequences of global warming. If floating glaciers melt, ocean levels will not be affected. However, if the ice over land melts, we can expect increased ocean levels. 7. The Environmental Protection Agency (EPA) website (www.epa.gov/acidrain/education/) includes good information about acid precipitation and teaching ideas. 8. The SETI (Search For Extraterrestrial Intelligence) Institute’s Mission is to explore, understand and explain the origin, nature, and prevalence of life in the universe (www.seti.org). Your students might enjoy exploring this respected scientific organization.

Figure 2.13 Why ice floats.

Student Misconceptions and Concerns 1. Students are unlikely to have carefully considered the four special properties of water that are apparent in our lives. However, these properties are of great biological significance and are often familiar parts of our lives. The connections between these properties and personal experiences can invest great meaning into a discussion of water’s properties. A homework assignment asking for three examples of each of these properties in each student’s experiences will require reflection and potentially produce meaningful illustrations. Similarly, quizzes or exam questions matching examples of each property to a list of the properties requires high-level evaluative analysis. 2. Students at all levels struggle with the distinction between heat and temperature. Students might also expect that all ice is about the same temperature, 0˚C. Redefining and correcting misunderstandings often takes more class time and energy than introducing previously unknown concepts. Teaching Tips 1. Here is a way to have your students think about the sticky nature of water in their lives. Ask them to consider the need for a towel after a shower or a bath. Once we get out of the shower or bath, we have left the source of water. So why do we need the towel? The reason we need a towel to dry off is that water is still clinging to our bodies because water molecules are polar. The molecules on cell surfaces are also polar, so our skin and the water both stick to each other. 2. Some students may be intrigued if you tell them that you too can stand on the surface of water—when it is frozen. Thus, it is necessary to note a liquid water surface when talking about surface tension. 3. Have students compare the seasonal ranges of temperatures of Anchorage and Fairbanks, Alaska. (Many websites, such as Yahoo, provide weather information about various cities.) These two northern cities have large differences in their annual temperature ranges. Make the point that the coastal location of Anchorage moderates the temperature. 4. Several versions of the following analogy are easy to relate to students. (a) Ask students how the average on an exam would be affected if the brightest students didn’t take the test. (b) The authors note that the performance of a track team would drop if the fastest sprinters didn’t compete. In both analogies, removing the top performers lowers the average just as the evaporation of the most active water molecules cools the evaporative surface. 5. It is not the heat, it is the humidity. The efficiency of evaporative cooling is affected by humidity. As humidity rises, the rate of evaporation decreases, making it more difficult to cool our heat-generating bodies on a warm and humid summer day. 6. Ask your students if the ocean levels would change if ice didn’t float. They can try this experiment to find out. Place several large chunks of ice in a glass and fill the glass up completely with water to the top rim. Thus, the ice cubes should be sticking up above the top of the filled glass. Will the glass overflow when the ice melts? (No.) This phenomenon is important when we consider the potential consequences of global warming. If floating glaciers melt, ocean levels will not be affected. However, if the ice over land melts, we can expect increased ocean levels. 7. The Environmental Protection Agency (EPA) website (www.epa.gov/acidrain/education/) includes good information about acid precipitation and teaching ideas. 8. The SETI (Search For Extraterrestrial Intelligence) Institute’s Mission is to explore, understand and explain the origin, nature, and prevalence of life in the universe (www.seti.org). Your students might enjoy exploring this respected scientific organization.

Student Misconceptions and Concerns 1. Students are unlikely to have carefully considered the four special properties of water that are apparent in our lives. However, these properties are of great biological significance and are often familiar parts of our lives. The connections between these properties and personal experiences can invest great meaning into a discussion of water’s properties. A homework assignment asking for three examples of each of these properties in each student’s experiences will require reflection and potentially produce meaningful illustrations. Similarly, quizzes or exam questions matching examples of each property to a list of the properties requires high-level evaluative analysis. 2. Students at all levels struggle with the distinction between heat and temperature. Students might also expect that all ice is about the same temperature, 0˚C. Redefining and correcting misunderstandings often takes more class time and energy than introducing previously unknown concepts. Teaching Tips 1. Here is a way to have your students think about the sticky nature of water in their lives. Ask them to consider the need for a towel after a shower or a bath. Once we get out of the shower or bath, we have left the source of water. So why do we need the towel? The reason we need a towel to dry off is that water is still clinging to our bodies because water molecules are polar. The molecules on cell surfaces are also polar, so our skin and the water both stick to each other. 2. Some students may be intrigued if you tell them that you too can stand on the surface of water—when it is frozen. Thus, it is necessary to note a liquid water surface when talking about surface tension. 3. Have students compare the seasonal ranges of temperatures of Anchorage and Fairbanks, Alaska. (Many websites, such as Yahoo, provide weather information about various cities.) These two northern cities have large differences in their annual temperature ranges. Make the point that the coastal location of Anchorage moderates the temperature. 4. Several versions of the following analogy are easy to relate to students. (a) Ask students how the average on an exam would be affected if the brightest students didn’t take the test. (b) The authors note that the performance of a track team would drop if the fastest sprinters didn’t compete. In both analogies, removing the top performers lowers the average just as the evaporation of the most active water molecules cools the evaporative surface. 5. It is not the heat, it is the humidity. The efficiency of evaporative cooling is affected by humidity. As humidity rises, the rate of evaporation decreases, making it more difficult to cool our heat-generating bodies on a warm and humid summer day. 6. Ask your students if the ocean levels would change if ice didn’t float. They can try this experiment to find out. Place several large chunks of ice in a glass and fill the glass up completely with water to the top rim. Thus, the ice cubes should be sticking up above the top of the filled glass. Will the glass overflow when the ice melts? (No.) This phenomenon is important when we consider the potential consequences of global warming. If floating glaciers melt, ocean levels will not be affected. However, if the ice over land melts, we can expect increased ocean levels. 7. The Environmental Protection Agency (EPA) website (www.epa.gov/acidrain/education/) includes good information about acid precipitation and teaching ideas. 8. The SETI (Search For Extraterrestrial Intelligence) Institute’s Mission is to explore, understand and explain the origin, nature, and prevalence of life in the universe (www.seti.org). Your students might enjoy exploring this respected scientific organization.

Figure 2.16 The pH scale.

Figure 2.16a The pH scale.

Chapter 2 0 Essential Chemistry for Biology

Give an example of solid matter. 2. Give an example of liquid matter. 3. Give an example of gaseous matter. 4. Is all matter visible? 5. Does all matter take up space?

SOME BASIC CHEMISTRY Take any biological system apart, and you eventually end up at the chemical level. Matter is anything that occupies space and has mass. Matter is found on the Earth in three physical states: Solid Liquid Gas

H Rb K Na Li Fr Cs Sr Ca Mg Be Ra Ba Y Sc Ac La Zr Ti Rf Hf Nb V Db Ta Mo Cr Sg W Tc Mn Bh Re Ru Fe Hs Os Rh Co Mt Ir Pd Ni Uun Pt Xe Kr Uuo Rn Ag Cu Uuu Au Cd Zn Uub Hg Ar Ne In Ga Tl Al B Sn Ge Uuq Pb Si C Sb As Bi P N Te Se Uuh Po S O I Br At Cl F He Th Ce Pa Pr U Nd Np Pm Pu Sm Am Eu Lr Lu Cm Gd Bk Tb Cf Dy Es Ho Fm Er Md Tm No Yb 6 C 12 Figure 2.1

Twenty-five elements are essential to life. Four elements make up about 96% of the weight of the human body: Oxygen Carbon Hydrogen Nitrogen

Atoms Each element consists of one kind of atom. An atom is the smallest unit of matter that still retains the properties of an element Atoms are composed of subatomic particles. Central core consists of 2 kinds of particles: Proton, + charge Neutron, no electrical charge All atoms have the same number of protons. # of protons = atomic number + charge is balanced by an = number of – charged particles called electrons

The Atom ATOM: Simplest particle of an element that retains all of the properties of that element Atomic Number= # of Protons Atomic Mass Chemical Symbol

Nucleus Protons Neutrons Electrons Nucleus Cloud of negative charge 2 electrons 2 2 2 Figure 2.4

Elements differ in the number of subatomic particles in their atoms. The number of protons, the atomic number, determines which element it is. An atom’s mass number is the sum of the number of protons and neutrons. Mass is a measure of the amount of matter in an object.

Chemical Bonding Inert elements (last column on periodic table) have their outermost energy level fully occupied by electrons Reactive elements do not have their outermost energy level fully occupied by electrons Octet rule – except for the first shell which is full with two electrons, atoms interact in a manner to have eight electrons in their valence shell

Isotopes Isotopes are alternate mass forms of an element. Isotopes have the same number of protons and electrons, but they have a different number of neutrons.

The nucleus of a radioactive isotope decays, giving off particles and energy. Radioactive isotopes have many uses in research and medicine. They can be used to determine the fate of atoms in living organisms. They are used in PET scans to diagnose heart disorders and some cancers.

Electron Arrangement and the Chemical Properties of Atoms Electrons determine how an atom behaves when it encounters other atoms. Electrons orbit the nucleus of an atom in specific electron shells. The farther an electron is from the nucleus, the greater its energy. The number of electrons in the outermost shell determines the chemical properties of an atom. © 2010 Pearson Education, Inc.

First electron shell can hold 2 electrons Outer electron shell can hold 8 electrons Hydrogen H Atomic number = 1 Carbon C Atomic number = 6 Nitrogen N Atomic number = 7 Oxygen O Atomic number = 8 Electron Figure 2.5

Chemical Bonding and Molecules Elements can combine to form compounds by action of electrons. Compounds are substances that contain two or more elements in a fixed ratio. Common compounds include NaCl (table salt) H2O (water) Chemical reactions enable atoms to give up or acquire electrons to complete their outer shells. Chemical reactions usually result in atoms Staying close together Being held together by chemical bonds

Ionic Bonds When an atom loses or gains electrons, it becomes electrically charged. Charged atoms are called ions. Ionic bonds are formed between oppositely charged ions.

Covalent Bonds A covalent bond forms when two atoms share one or more pairs of outer-shell electrons. Atoms held together by covalent bonds form a molecule. The number of covalent bonds an atom can form is equal to the number of additional electrons needed to fill its outer shell. Animation: Covalent Bonds

Electron sharing Atoms joined into a molecule via covalent bonds Figure UN2-7

Name molecular formula Hydrogen gas H2 Oxygen gas O2 Methane CH4 Electron configuration Structural formula Space-filling model Ball-and-stick model Single bond a pair of shared electrons Double bond two pairs of shared electrons Figure 2.7

Hydrogen Bonds Water is a compound in which the electrons in its covalent bonds are shared unequally. This causes water to be a polar molecule, one with opposite charges on opposite ends. Animation: Water Structure

H H O slightly  slightly  slightly – Figure UN2-2

The polarity of water results in weak electrical attractions between neighboring water molecules. These interactions are called hydrogen bonds.

Water’s Life-Supporting Properties Life on Earth began in water and evolved there for 3 billion years. Modern life remains tied to water. Your cells are composed of 70%–95% water. The abundance of water is a major reason Earth is habitable. The polarity of water molecules and the hydrogen bonding that results explain most of water’s life-supporting properties. Water molecules stick together. Water has a strong resistance to change in temperature. Frozen water floats. Water is a common solvent for life.

The Cohesion of Water Water molecules stick together as a result of hydrogen bonding. This is called cohesion. Cohesion is vital for water transport in plants.

Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid. Hydrogen bonds give water an unusually high surface tension.

How Water Moderates Temperature Because of hydrogen bonding, water has a strong resistance to temperature change. Water can absorb and store large amounts of heat while only changing a few degrees in temperature.

The Biological Significance of Ice Floating When water molecules get cold enough, they move apart, forming ice. A chunk of ice has fewer molecules than an equal volume of liquid water. Ice floats because it is less dense than the liquid water around it. If ice did not float, ponds, lakes, and even the oceans would freeze solid. Life in water could not survive if bodies of water froze solid.

Hydrogen bond Liquid water Ice Figure 2.13

Water as the Solvent of Life A solution is a liquid consisting of a homogeneous mixture of two or more substances. The dissolving agent is the solvent. The dissolved substance is the solute.

Acids, Bases, and pH A chemical compound that releases H+ to solution is an acid. A compound that accepts H+ and removes it from solution is a base. To describe the acidity of a solution, chemists use the pH scale. Buffers are substances that resist pH change. Buffers Accept H+ ions when they are in excess Donate H+ ions when they are depleted

Basic solution Neutral solution Acidic solution Oven cleaner Household bleach Human blood Pure water Grapefruit juice, soft drink Lemon juice, gastric juice Household ammonia Milk of magnesia Seawater Tomato juice Urine pH scale 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Increasingly acidic greater H concentration Increasingly basic lower H concentration Neutral [H+]  [OH–] Figure 2.16

Basic solution Neutral solution Acidic solution Figure 2.16a