Chemistry, The Molecular

Chemistry, The Molecular Science, 5e John Moore, Conrad Stanitski

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Chapter 1: The Nature of Chemistry 1

Chapter 1: The Nature of Chemistry

Teaching for Conceptual Understanding Chemistry – The Molecular Science encourages students to think about chemistry at three different levels: the macroscopic, the particulate or nanoscale, and the symbolic. Science education research has shown that an understanding of just one level does not imply an understanding of the others. Whenever possible use all three levels in your teaching and assessment of student learning. Figure 1.17 illustrates the macroscopic and particulate levels for solid ice, liquid water, and water vapor. Have students visualize or draw other simple molecules, such as bromine or mercury, at the particulate level in three different states.Section 1-3 discusses how science is done, i.e., how observations lead to a hypothesis, how the hypothesis leads to more observations or experimentation, which in turn can lead to a law or theory. Students sometimes get the idea that science is a step-by-step procedure that takes place in a laboratory instead of a process that people can use everyday to solve problems and understand the world around them. It would be helpful to explain the process of science by using examples with which students can identify. Relevant examples will change over time, so be diligent in coming up with new examples from year to year.Learning chemistry is like learning a foreign language because of the extensive use of new terminology. Students will make quicker and stronger associations between terms and concepts when the root or origin of the terms is explained. For example, in this chapter the terms nanoscale and microscale are introduced. This is a good time to reinforce the size of the metric prefixes “micro-” and “nano-” as explanations for the terminology.Suggestions for Effective Learning Keep in mind that students are excited and ready to work the first day of class. It is best not to waste this valuable moment by simply reviewing the syllabus and dismissing the students. Have demonstrations, multimedia material, and activities ready to engage them in learning.If you plan on using demonstrations during the course, show some of your favorites during the first class. A few easy demonstrations that always grab students’ attention are: Igniting hydrogen filled balloons, freezing flowers in liquid nitrogen, and dropping pieces of sodium or potassium into water.In addition to the cooperative learning activities suggested below, consider having the students write briefly on their impressions of chemistry, or what properties solids, liquids, and gases have, or how they use the scientific process in solving their everyday problems.Finally, take a few minutes to explain something about yourself. The students will respect and engage with you better when they feel they understand who you are, why you’re there, and what you care about. Their college experience as well as their relationship with you is enriched by a small amount of personal information.Cooperative Learning Activities Whether you intend to use cooperative learning activities during class time or not, it is very important for students to get acquainted with each other. Set aside at least five minutes during your first class for students to meet others seated around them. In addition to exchanging personal information, e.g., name, hometown, major, have them share their feelings about taking a college chemistry course. Some students feel anxious about taking chemistry; however, knowing how others feel can help them see that they are not alone.Questions, problems, and topics that can be used for Cooperative Learning Exercises and other group work are: • Questions for Review and Thought: 4, 5, 7-8, 11-12, 37-38, 47-48, 63-64, 98-99, 117, 118 • Conceptual Challenge Problems: CP1.A, CP1.B, CP1.C, CP1.D, CP1.E, CP1.F, CP1.G, and CP1.H • Choose one or two statements from Section 1-1 that are most relevant to your students. Have the students spend five minutes writing down their ideas, then have them share those ideas with others around them in a short discussion. Another group activity is to have students list three to five ways that they have used chemicals today. 2 / 4

Chapter 1: The Nature of Chemistry 2

End-of-Chapter Solutions for Chapter 1 Summary Problem Result: 3 ×1015 J; water is a compound, none are mixtures; See nanoscale diagram below, CH4 (g) + O2 (g)CO2 (g) + 2 H2 (g) Analyze and Plan: Given the number of electric vehicles, the average miles each drives per year, the relationship between miles and kilometers, the energy efficiency of each vehicle, and some relationships between energy units, calculate the total energy needed for these vehicles.

Execute:

€ 300,000vehicles×1yr× 10,000mi/vehicle yr # $ % & '

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1.6km 1mi # $ % & '

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1kW e h 6km # $ % & '

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1000W e h 1kW e h # $ % & '

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3.6PJ 10 12 W e h # $ % % & ' ( ( =3PJ

Because 1PJ = 1 ×1015 J, this is 3 ×1015 J of energy. Reasonable Result Check: The answer in petajoules is a convenient number, 3, which is consistent with PJ being commonly used to measure such energies.Explanation: Given information about reactions involving hydrogen, water, and oxygen, determine if these are elements, compounds, or mixtures.Because the substance called water is formed using hydrogen and hydrogen is recreated when water is decomposed, it is certain that water is a compound. The information provided does not make it clear whether the substances labeled hydrogen or oxygen are compounds or elements, but they are not mixtures because each time one destroyed or created they can be isolated and characterized as a pure substance.Explanation: Given chemical formulas and information about a reaction write nanoscale and symbolic representations of the reaction that are consistent with modern atomic theory.The parts of modern atomic theory that applies to this example are: Compounds are formed by the chemical combination of two or more different kinds of atoms and a chemical reaction involves joining, separating, or rearranging atoms.A molecule of methane is composed of one atom of carbon combined with four atoms of hydrogen. A molecule of oxygen is composed of two atoms of oxygen combined together. These two substances together represent the reactants in the first nanoscale box and on the left side of the symbolic representations shown below. A molecule of carbon dioxide is composed of one atom of carbon combined with two atoms of oxygen. A molecule of hydrogen is composed of two atoms of hydrogen combined together. One carbon dioxide molecule and two hydrogen molecules represent the products in the second nanoscale box and on the right side of the symbolic representations shown below. Because the reactants include four atoms of hydrogen, there are two molecules of H2 represented in the products to account for all the hydrogen atoms present initially.

methane and oxygen gas carbon dioxide gas and hydrogen gas CH4(g) + O2(g) CO2(g) + 2 H2(g) 3 / 4

Chapter 1: The Nature of Chemistry 3

End-of-Chapter Solutions for Chapter 1 Questions for Review and Thought Review Questions

• Result/Explanation: The structure of a molecule refers to the way atoms are connected together in the molecule

and to the three dimensional arrangement of the atoms relative to one another. Structure is important because it is the key to the properties and reactivity of a molecule.

• Result/Explanation: Quantitative observations of a piece of electronics must include numerical information;

whereas qualitative observations do not involve numerical details. For example, a television: Quantitative observations might include the dimensions of the screen and case, the various control settings (volume level, channel selection, etc.), the screen resolution, the power supply requirements, its position in the room, on-off, etc. The qualitative observations might include the color of the case, the types and locations of control buttons or knobs, the quality of the audio output, the quality of the video image, and the type of connection to a video signal (antenna, cable, satellite, internet, etc.).

• Result/Explanation: A scientific law (a) summarizes and explains a wide range of experimental results, (b) has

not been contradicted by experiments, and (c) is capable of predicting unknown results. Some laws are described in Atomic Theory. Two of these laws are: the law of conservation of mass (i.e., there is no detectable change in mass during an ordinary chemical reaction.) and the law of constant composition (i.e., A chemical compound always contains the same elements in the same proportion by mass.).

• Result/Explanation: A theory is a unifying principle that explains a body of facts and the laws based on them –

hence a theory is our reason for believing in the law; whereas a law gives just a summary conclusion of a wide range of experimental results. Models are used to make theories more concrete, often in physical or mathematical form – hence a model is our way of looking at the theory in detail.

• Result/Explanation: Chemists build the bridge between the nanoscale world into the microscale world. The

details of the nanoscale world often profoundly affect the activity of a chemical in the micro- and macroscopic worlds. A specific example is the determination of the mechanism of paclitaxel activity in the search for improved anticancer drugs.

• Result/Explanation: (Described in Section 1-7) Two examples of when purity of a substance is important: The

purity of the elemental silicon is important to the production of electronic chips. To properly characterize the properties of a substance, it is necessary to test the substance in its pure state.Topical Questions Why Care About Chemistry? (Section 1-1)

• Result/Explanation: Important issues change from year to year, and sometimes even from month to month or

even day to day. A good website for seeking up-to-date information on a wide range of scientific topics is http://www.sciencedaily.com/. In summer of 2013, the following issues were big: • forensics • energy technology, renewable energy, alternative fuels • nanotechnology • environmental issues: climate, air quality, pollution, global warming, acid rain • cancer, stem cells, brain tumors, heart disease, medical technology • transportation sciences • nature of water • materials in electronic devices (batteries, display, functionality, etc.)

• Result/Explanation: Several questions related to chemistry and science phenomena are given in Section 1-1.
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