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Challenge Study Guide ® PASSPORT TO SCIENCE EXPLORATION CHEMISTRY CONNECTIONS CREATED BY THE CHEMICAL EDUCATIONAL FOUNDATION® Copyright 2017 by the Chemical Educational Foundation® Welcome to the You Be The Chemist Challenge®! What is everything around us made of? How does it form? Why do different substances have different properties? How does one thing change into something completely different? We’ll answer all of these questions—and many more—in the Passport to Science Exploration. These materials show you how the fascinating world of chemistry applies to your everyday life, and teach you how to think about and solve problems like a scientist. Chemistry is behind everything from making candy to powering rockets! Studying chemistry can teach you how to question assumptions, find solutions, and push the boundaries of what we know. In these materials, you’ll learn how the elements react and combine to form everything around us. But the ability to think like a chemist goes beyond the periodic table. Participating in the Challenge prepares you to tackle whatever scientific puzzles come your way, from math to biology to computer science. Whether your career leads you to become an oceanographer, a doctor, a writer, or an entrepreneur, you can still be a scientist by applying the problem-solving skills you are about to learn. Preparing for the State Challenge The best way to prepare for the Challenge is to review the information contained in the study materials and to fully understand how to use it to solve problems. The Passport to Science Exploration is divided into three parts that each prepare you for a level (or levels) of the Challenge: • The Core of Chemistry: Local Challenge • Chemistry Connections: State Challenge • Chemistry Concepts in Action: National Challenge This portion, Chemistry Connections, builds on the fundamentals from The Core of Chemistry and takes you a step further as you explore the world of chemistry. You need to be familiar with both Chemistry Connections and The Core of Chemistry for State and National Challenge competitions. Use the tips below to get the most out of CEF’s study materials: 1. Review the Objectives list provided at the beginning of each section to become familiar with the topics you will learn. Once you have finished the entire chapter, go back and review the Objectives. If you aren’t sure you can complete the tasks listed, try reading the section again or seeking additional information (some ideas for where to look for help are listed on the next page). 2. Go through and answer the questions in the Think About It... bubbles. These questions help you practice important problem-solving skills. See if you can work through all of them on your own before looking at out- side resources or asking for help. You Be The Chemist Challenge® Passport to Science Exploration 1 3. Make sure to read not only the main text, but also the Example, Quick Fact, History, and Element boxes. These boxes deepen your understanding of the concepts and highlight important applications. 4. Challenge yourself to come up with additional questions based on the topics covered, and try to answer them using the information you’ve learned. 5. Use the You Be The Chemist® Activity Guides to explore chemistry in a real-world setting. To access the Ac- tivity Guides, ask a teacher or parent to download them for free from CEF’s website. We also encourage you to explore outside resources and ask others for help. The more you explore, the more likely you are to find answers to the questions you have about the world around you! The following are some good ways to get more information: • Ask a parent or teacher to explain concepts and give you additional examples. • Go over the material with a friend and work together to answer any questions you have. • Find a printed book or publication—such as another chemistry textbook—to hear things explained in a different way. • Explore the many online resources that are available. Online resources are free and often updated, but you should make sure that any sources you use are reliable and from a credible source. Some supplementary resources are provided on CEF’s website, www.chemed.org. Visit the Challenge Study Materials page (www.chemed.org/programs/challenge/study-materials/) to access: • A list of the major topics included in the study materials; • Sample questions to illustrate how the concepts can be applied to problems; • CEF’s version of the periodic table. If you are not sure about how to prepare for a particular level of the competition, ask your teacher or Local/State Challenge Organizer. You may also contact the Chemical Educational Foundation® (CEF) at [email protected]. Challenge questions are derived from the information contained in CEF’s study materials, but are not limited solely to this information. We encourage you to seek additional examples and explanations of chemistry concepts from your teachers, peers, and other science resources. Doing so will help you answer questions that require you to connect concepts and apply your knowledge of chemistry to both familiar and unfamiliar situations. Go ahead and get started—good luck! 2 You Be The Chemist Challenge® Passport to Science Exploration TABLE OF CONTENTS CHEMISTRY CONNECTIONS I. CHEMICAL FORMULAS Lewis Symbols . 4 Writing Chemical Formulas . 7 Chemical Formulas of Common Compounds . 9 Naming Chemical Compounds . 9 II. FORCES OF ATTRACTION Intramolecular Forces. 1 5 Periodic Trends . 1 6 Types of Chemical Bonds . 2 1 Bonding Review . 2 6 Lewis Structures . 27 Gravity . 3 1 Magnetism. 3 2 III. CHEMICAL REACTIONS Visualizing Chemical Reactions . 3 4 Rates of Chemical Reactions . 3 6 Energy of Chemical Reactions. 3 8 General Types of Chemical Reactions . 4 0 Oxidation-Reduction (Redox) Reactions . 4 1 Chain Reactions . 4 2 Reversible Reactions and Equilibrium . 4 3 IV. BALANCING CHEMICAL EQUATIONS Conservation of Mass . 4 4 Balancing Chemical Equations . 4 6 V. ACIDS, BASES, AND pH Acids. 47 Bases . 47 The pH Scale . 4 8 Strength of Acids and Bases . 4 9 Indicators . 5 0 VI. RADIOACTIVITY AND NUCLEAR REACTIONS Radioactivity. 5 1 Nuclear Energy . 5 5 Human-made Elements. 57 You Be The Chemist Challenge® Passport to Science Exploration 3 SECTION I: CHEMICAL FORMULAS OBJECTIVES • Identify the Lewis symbols for different elements. • Identify and write chemical formulas using chemical symbols. • Recognize common chemical compounds and their formulas. • Use the guidelines of chemical nomenclature to name chemical compounds. LEWIS SYMBOLS Scientists have many different ways to represent an atom of an element. One way is to write the element’s ground-state electron configuration (see the subsection on Electron Configuration from The Core of Chemistry). Another way is to use Lewis symbols. Lewis symbols (also known as electron dot structures) contain the element’s chemical symbol and dots that represent the high-energy outermost electrons, called valence electrons. Remember, each element has a unique chemical symbol of one or two letters, as shown on the periodic table. VALENCE ELECTRONS Valence electrons are the electrons in the highest energy level, located in the electron shell the farthest from the nucleus of an atom (see Periodic Trends). Atoms often react using their valence electrons, so looking at a Lewis symbol and knowing how many valence electrons an element has can help determine how it will react with other elements. The electrons not in the highest energy level are known as core electrons, and are not usually involved in chemical reactions. Most main group elements (elements in groups 1-2 and groups 13-18) can have up to eight valence electrons. Transition metals (groups 3-12) do not follow this rule. Groups 1-2 and 13-18 (the main group elements) all follow the same pattern of valence electrons. Moving from left to right across the periodic table, one electron is added with each group. The number of valence electrons increases by Quick Fact one with each group from left to right, not including the The ground-state electron transition metals (groups 3-12, colored purple), as configuration of an atom shows the shown on the following page. lowest energy state of the atom. In the presence of light, electrons can sometimes absorb energy to jump to a higher energy level, changing the electron configuration. This is called an excited state. 4 4 CHEMISTRY CONNECTIONS, SECTION I: Chemical Formulas Valence 1 2 3 4 5 6 7 8 electrons Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 • Groups 1-2: the number of valence electrons equals the element’s group number on the periodic table. For example, calcium is in group 2 and has two valence electrons. • Groups 13-18: the number of valence electrons is ten fewer than the element’s group number. For example, oxygen is in group 16 and has six valence electrons. • Groups 3–12: the process is not so simple for the transition metals. Transition metal atoms can use electrons from their inner shells as valence electrons, so the number of valence electrons varies. • Group 18: the noble gases in the last group on the periodic table each have eight valence electrons. Since eight is the maximum number of electrons that can fit into each of these atom’s outermost energy level, each of the noble gases has a full octet. Atoms are most stable when they have eight valence electrons, making the noble gases generally unreactive. The noble gas helium is an exception with only two valence electrons. Its outermost energy level is only a 1s orbital, which is full with two electrons, making helium stable. EXAMPLE: One beryllium (Be) atom has four electrons and an electron configuration of 1s22s2.
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