Chemistry, Quarter 3, Unit 3.1. Periodic Trends. Overview

Transcription

1 Chemistry, Quarter 3, Unit 3.1 Periodic Trends Overview Number of instructional days: 8 (1 day = 50 minutes) Content to be learned Explain how the properties of elements and the location of elements on the periodic table are related. Explain the basis for the arrangement of the elements within the periodic table (trends, valence electrons, reactivity, electronegativity, ionization). Essential questions How are the properties of elements related to their location on the periodic table? Science processes to be integrated Create and interpret graphs. Identify patterns and trends in data. Use evidence to draw conclusions. Analyze and create models, diagrams, charts, and data tables. Make predictions. Use appropriate tools and techniques. How is the arrangement of the elements within the periodic table related to its trends, valence electrons, reactivity, electronegativity, and ionization? 31

2 Chemistry, Quarter 3, Unit 3.1 Periodic Trends (8 days) Written Curriculum Grade-Span Expectations PS1 - All living and nonliving things are composed of matter having characteristic properties that distinguish one substance from another (independent of size or amount of substance). PS1 (9-11) POC 3 Explain how properties of elements and the location of elements on the periodic table are related. PS1 (9-11)-3 Students demonstrate an understanding of characteristic properties of matter by 3a identifying and explaining the basis for the arrangement of the elements within the periodic table (e.g. trends, valence electrons, reactivity, electronegativity, ionization). Clarifying the Standards Prior Learning In grades K 4, students identified, compared, and sorted objects by using attributes of properties to state why objects are grouped together. They also cited evidence to support conclusions about why objects are or are not grouped together. Students identified and compared solids and liquids. They also described the properties of solids and liquids and made predictions about the changes in the state of matter when heat is added or taken away. In grades 3 and 4, students reviewed the comparison of properties of solids and liquids and were introduced to the properties of gases. They also made logical predictions about the changes in the state of matter when adding or taking away heat (e.g., boiling water, condensation, evaporation). In grades 5 and 6, students demonstrated an understanding characteristic properties of matter by classifying and using characteristics (e.g., solid, liquid, gas). They also demonstrated an understanding of characteristic properties of matter by comparing the masses of objects of equal volume made of different substances. In grades 7 and 8,students were introduced to the structure of an atom and modeled the structure of an atom. They demonstrated an understanding characteristic properties of matter by classifying and using characteristics (e.g., solid, liquid, gas. metal, nonmetals). Students demonstrated an understanding of the structure of matter by using models or diagrams to show the difference between atoms and molecules. They also explained that when substances undergo physical changes, the appearance may change but the chemical makeup and chemical properties do not. Students in grade 8 classified common elements and compounds using symbols and simple chemical formulas. They also interpreted the symbols and formulas of simple chemical equations, explained that when substances undergo chemical changes to form new substances the properties of the new combinations may be very different from those of the old, and used symbols and chemical formulas to show simple chemical rearrangements that produce new substances (chemical change). In Unit 1.3, students were introduced to the organization of the periodic table. In Unit 2.2, they explained how the outermost electrons determine an atom s interaction with other atoms. Students wrote electron 32

3 Chemistry, Quarter 3, Unit 3.1 Periodic Trends (8 days) configurations and developed basic models of electron structure. They wrote formulas for compounds in Unit 2.3 as well as basic chemical reactions and nomenclature in Unit 2.4. Current Learning Although students have written formulas for compounds and classified and compared substances using characteristic properties, they have never been formally introduced to the basis for the arrangement of the elements within the periodic table (e.g., trends in valence electrons, reactivity, electronegativity, and ionization energy). This puts the periodic table arrangement at a developmental level. Using electron configurations previously learned during Unit 2.2, students must now incorporate the new concept of an atom s valence electrons to the organization and trends in the periodic table. This puts the idea of trends in properties at a developmental level, while basic electron configuration is at the reinforcement level of instruction. Using an atom s electron configuration, students identify the atom s valence electrons. They define and determine an atom s electronegativity and ionization energy. Students explain how the properties of elements and the location of elements on the periodic table are related to their reactivity and how the trends of valence electrons, reactivity, electronegativity, and ionization energy determine the arrangement of the periodic table. A summative assessment in the form of a common performance-based task could be a task like Meteorite, which focuses on determining the identity of an element based on given data. Students create and interpret graphs of periodic trends. They identify patterns and trends in data to determine how the periodic table was arranged. Students use evidence from data to draw conclusions. They analyze and create models, diagrams, charts, and data tables related to the periodic table. Students appropriately use tools and techniques in science. All of these activities help bolster student understanding of the periodic table and are used to support this learning. Hands-on activities such as It s in the Cards (Flinn Scientific), Alien Periodic Table, or The Nuts and Bolts of Chemistry focus on arrangement of elements based on the studied properties to discover trends. Future Learning The next unit students will encounter involves bonding. Electron configuration ultimately determines the type of bond that is formed from elements. Students will determine the ionic or molecular character of a product, which is the type of bond that is formed. Writing thermochemical and nuclear equations is the next step from writing balanced equations. Additional Findings In science, although chemical compounds are regarded as single substances containing two or more elements chemically combined in a fixed proportion by mass, several studies have found that children frequently describe compounds as though they are mixtures of elements. This may be because they have not formed a science conception of chemical combination of the elements included in a compound s name. Many 15-year-olds, despite experience with several related science tasks, appeared to be unaware that in most compounds the proportions of combining elements are fixed. (Making Sense of Secondary Science, pp. 75 and 76) Studies have shown that the way in which pupils perceive a chemical or physical change may determine whether they regard material substance as being conserved during that change. For example, if their view 33

4 Chemistry, Quarter 3, Unit 3.1 Periodic Trends (8 days) of a particular change is dominated by the apparent disappearance of some material(s), pupils are unlikely to conserve the mass. If they regard gases as weightless, they are unlikely to conserve overall weight and mass in reactions that involve gases. (Making Sense of Secondary Science, p. 77) Many high school students think that models are useful for visualizing ideas and communication purposes. A mathematic model may give insight about how something really works or may fit observations very well without any intuitive meaning. (NSDL Models nsdl.org/?id=sms-map-2408) 34

5 Chemistry, Quarter 3, Unit 3.2 Bonding Overview Number of instructional days: 8 (1 day = 50 minutes) Content to be learned Explain/model how the electron configuration of atoms governs how atoms interact with one another during covalent bonding. Explain/model how the electron configuration of atoms governs how atoms interact with one another during ionic bonding. Explain/model how the electron configuration of atoms governs how atoms interact with one another during hydrogen bonding. Essential questions How does the electron configuration of atoms determine the types of bonds that atoms make? Science processes to be integrated Use evidence to draw conclusions. Use, create, and analyze data. Use, create, and analyze models. Compare and contrast. Use tools and techniques. What distinguishes a hydrogen bond from an ionic or covalent bond? 35

6 Chemistry, Quarter 3, Unit 3.2 Bonding (8 days) Written Curriculum Grade-Span Expectations PS1 - All living and nonliving things are composed of matter having characteristic properties that distinguish one substance from another (independent of size or amount of substance) PS1 (9-11) MAS+ FAF 4 Model and explain the structure of an atom or explain how an atom s electron configuration, particularly the outermost electron(s), determines how that atom can interact with other atoms. PS1 (9-11) 4 Students demonstrate an understanding of the structure of matter by 4c explaining or modeling how the electron configuration of atoms governs how atoms interact with one another (e.g. covalent, hydrogen and ionic bonding). Clarifying the Standards Prior Learning In grades 5 and 6, students distinguished between solutions, mixtures, and pure substances (e.g., between compounds and elements). In grades 7 and 8, students used models to show the difference between atoms and molecules. They used symbols and chemical formulas to show simple chemical arrangements that produce new substances during a chemical change. Students explained that when substances undergo chemical change to form new substances, the properties of the new combinations may be very different from those of the old. Current Learning Although students have spent a considerable amount working with an atom s electron configuration in previous chemistry units (Units 2.3 and 3.1), they are at a developmental level when this is applied to the type of bonds atoms make. Instruction around the forces that exist between atoms and compounds should be presented at an introductory level. Students have not used valence electrons to predict molecular shape; therefore, this is at a developmental level. Although students have used models to show the difference between atoms and molecules, they have not constructed compounds. This is at a developmental level. In Units 2.3 and 3.1, students wrote electron configurations and determined the valance electrons in an atom. In this unit, they further this knowledge to determine what types of bonds atoms make due to their electron configurations. Students explain how the electron configuration of atoms governs how atoms interact with one another during ionic bonding and covalent bonding. They need to explain how the equal or unequal sharing of electrons (bond polarity) results in intermolecular forces of many types, specifically hydrogen bonding. Students use valence electrons to draw Lewis Dot structures for compounds to enable them to determine the type of shapes that are found in molecular compounds. Students may be introduced to the quantitative 36

7 Chemistry, Quarter 3, Unit 3.2 Bonding (8 days) idea of bond polarity through the calculation of dipoles using electronegativity values to take the instruction to a deeper level using drill and practice. Students use evidence from an investigation to draw conclusions. These may include investigations that explore the chemical and physical properties that differentiate between ionic and molecular compounds (i.e., melting point, boiling point, conductivity, solubility). Students use, create, analyze, and interpret data and models such as molecular geometry labs that relate a molecule s shape to its bonding character. Molecular modeling kits or online simulations are resources that can be used to illustrate the concepts. Students draw Lewis Dot diagrams of compounds and use these diagrams to predict the shape of molecules and again discover that shape has an effect on chemical and physical properties. They then compare and contrast properties of the substances. Throughout this unit, students need to appropriately use tools and techniques in science. Hand-held data collection probes may be used to enhance technology skills in this unit. The content in this unit is different from previous units because it requires students to work with an atom s electron configuration. Students now apply valence electrons to the type of bonds atoms make. Forces between atoms and compounds (e.g., intermolecular and intramolecular attractions) are now addressed. Students use valence electrons to predict molecular shape. Although students have used models to show the difference between atoms and molecules, they have not constructed compounds using VSEPR (valence shell electron pair repulsion) theory and how it relates to shape. Future Learning Intermolecular forces will enable students to understand the basis of the gas laws. In Biology, hydrogen bonding is essential to the understanding of the processes of life. Additional Findings Although the GSEs do not mandate that students learn Lewis Dot Structure writing, it is essential that they can do this if they are expected to learn how bonding occurs. The shapes of molecules determine the type of forces that exist between molecules. There are many types of intermolecular forces that exist between molecules (e.g., Van Der Waals forces and London Dispersion Forces); however, the GSE only specifies hydrogen bonding. All substances are composed of invisible particles and made up of a limited number of basic ingredients or elements. These two merge into the idea that combining the particles of the basic ingredients differently leads to millions of materials with different properties. (Benchmarks for Science Literacy, pp ) Some strategies to help students/teachers overcome the challenges presented by this unit are to describe the complexity of atoms gradually, using evidence and explanations from several connected story lines. Repeated exposure to this concept through the use of investigations as well as real-world examples may help. (Benchmarks for Science Literacy, p. 75). 37

8 Chemistry, Quarter 3, Unit 3.2 Bonding (8 days) 38

9 Chemistry, Quarter 3, Unit 3.3 Energy Changes and Energy Relationships Including Chemical Reactions Overview Number of instructional days: 20 (1 day = 50 minutes) Content to be learned Describe or diagram the transformation of energy that occurs in systems during endothermic and exothermic reactions. Identify, measure, calculate, and analyze qualitative and quantitative relationships associated with energy transfer or energy transformation in systems. Explain the energy flow in a given chemical reaction (e.g., exothermic reactions, endothermic reactions). Identify whether a chemical reaction or a biological process will release or consume energy. Essential questions How is energy transformed in systems during endothermic and exothermic reactions? How does the energy flow in endothermic and exothermic reactions? Science processes to be integrated Create and interpret graphs and diagrams. Compare and contrast systems. Observe, measure, and draw conclusions. Use, analyze, and interpret data. Use evidence from an investigation. Perform calculations. Use appropriate tools and techniques. What information do we need to show energy transfer relationships within a system? What types of information do we need to decide whether energy is released or consumed during reactions? 39

10 Chemistry, Quarter 3, Unit 3.3 Energy Changes and Energy Relationships Including Chemical Reactions (20 days) Written Curriculum Grade-Span Expectations PS 2 - Energy is necessary for change to occur in matter. Energy can be stored, transferred, and transformed, but cannot be destroyed. PS2 (9-11) POC+SAE -5 Demonstrate how transformations of energy produce some energy in the form of heat and therefore the efficiency of the system is reduced (chemical, biological, and physical systems). PS2 (9-11)-5 Students demonstrate an understanding of energy by 5a describing or diagramming the changes in energy (transformation) that occur in different systems (eg. chemical = exo and endo thermic reactions, biological = food webs, physical = phase changes). PS2 (Ext) 5 Students demonstrate an understanding of energy by 5aa Identifying, measuring, calculating and analyzing qualitative and quantitative relationships associated with energy transfer or energy transformation. PS2 (9-11) INQ+SAE -6 Using information provided about chemical changes, draw conclusions about and explain the energy flow in a given chemical reaction (e.g., exothermic reactions, endothermic reactions). PS2 (9-11) 6 Students demonstrate an understanding of physical, chemical, and nuclear changes by 6b identifying whether a given chemical reaction or a biological process will release or consume energy (endothermic and exothermic) based on the information provided (e.g. given a table of energy values for reactants and products or an energy diagram). Clarifying the Standards Prior Learning In grades K 4, students gained an understanding of physical changes by observing and describing physical changes such as freezing and thawing as well as heat flow and molecular motion. They demonstrated an understanding of states of matter by making logical predictions about the changes in the state of matter when adding or taking away heat such as ice melting and water freezing. Students demonstrated an understanding of energy by describing that objects change in temperature by adding or subtracting heat and how heat moves from warm objects to cold objects until both objects are at the same temperature. They demonstrated an understanding of states of matter by describing properties; identifying and comparing solids, liquids, and gases; and making logical predictions about the changes in the state of 40

11 Chemistry, Quarter 3, Unit 3.3 Energy Changes and Energy Relationships Including Chemical Reactions (20 days) matter when adding and taking away heat such as ice melting, water boiling or freezing or condensation/evaporation. In grades K 4, students demonstrated an understanding of energy by describing that objects change in temperature by adding or subtracting heat and how heat moves from warm objects to cold objects until both objects are at the same temperature. Students demonstrated an understanding of earth materials by describing, comparing, and sorting rocks, soils, and minerals by similar or different physical properties such as size, shape, color, texture, smell, weight, temperature, hardness, and composition. In grades 5 8, students demonstrated an understanding of the states of matter by using diagrams and models to differentiate among the characteristics of solids, liquids and gases. They predicted the effects of heating and cooling on the physical state. Students created diagrams or models that represent the states of matter at the molecular level and explain the effect of increased and decreased heat energy on the motion and arrangement of molecules. They observed the physical processes of evaporating and condensation or freezing and melting. Additionally, students described these changes in terms of molecular motion. They demonstrated an understanding of heat energy by designing a diagram, model, or analogy to show or describe the motion of molecules for a material in a warmer and cooler state. Students identified realworld applications where heat energy is transferred showing the direction that heat energy flows. Current Learning There is significant prior learning related to phase changes, so this section of the content should be presented at the reinforcement level. Experience with endothermic and exothermic reactions enables students to identify whether a chemical reaction or a biological process will release or consume energy. This is the first time that students have been exposed to endothermic and exothermic reactions therefore, this topic is at a developmental level. Although students have had experience with qualitative energy transfers, they have not spent time doing calculations or analyzing quantitative relationships of energy transfer or energy transformation. Therefore, this topic is at a developmental level. Students describe or diagram the transformation of energy that occurs in endothermic and exothermic reactions. They describe or diagram through graphing, the transformation of energy that occurs in phase changes. Students identify, measure, calculate, and analyze qualitative and quantitative relationships associated with energy transfer or energy transformation, for example the dissolving of calcium chloride in water can be observed and the change in temperature recorded. They compare and contrast systems involved in endothermic and exothermic reactions as well as the states of matter. Students observe, measure, and draw conclusions. Additionally, specific heats of metals can also be explored during laboratory activities calculating specific heat capacities of the metals. Students create and interpret graphs and diagrams of phase changes as well as endothermic and exothermic reactions. Here the heating and cooling curve for melting ice or boiling water may be used. They use, analyze, and interpret data relating to phase changes and whether heat is gained or lost during reactions. Students identify whether a chemical reaction or a biological process will release or consume energy given a table of energy values for reactants and products or an energy diagram. They perform quantitative heat flow or calorimetric investigations and use the evidence and perform calculations to draw conclusions to determine the energy released or consumed in the process Students have had significant prior learning related to phase changes in previous units and have experience with chemical reactions. They have had experience with qualitative energy transfers and have limited experience doing calculations or analyzing quantitative relationships of energy transfer. They have not used tables of energy values for reactants and products to identify whether a chemical reaction or 41

12 Chemistry, Quarter 3, Unit 3.3 Energy Changes and Energy Relationships Including Chemical Reactions (20 days) a biological process will release or consume energy. Calorimetric investigations and calculations have not been performed until this unit. Students use evidence from an investigation to draw conclusions. Students perform calculations when they quantitatively analyze relationships of energy transfer or energy transformations. They use the tools and techniques in science appropriately. Students use evidence from investigations to draw conclusions relating to the energy transfers or transformations that take place during phase changes as well as during endothermic and exothermic reactions. During these investigations, students perform calculations whereby they quantitatively analyze energy transformations. They describe or diagram the transformation of energy that occur in endothermic and exothermic reactions as well as phase changes. During these investigations, students observe, measure, analyze, and interpret data and draw conclusions. Future Learning Since unit 3.3 involves energy changes and chemical reactions, a thorough understanding of phase changes as well as endothermic and exothermic reactions is essential. This background knowledge is important to the understanding of the gas laws. All thermochemistry topics involve these energy transformations. Radiation involves the transfer of energy as well as fission and fusion in nuclear chemistry. In physics, the study of the transformation of energy focuses in the direction of electrical circuits changing electrical energy to light energy. Students will later explain the Law of Conservation of Energy as it relates to the efficiency (loss of heat) of a system. Energy transfer occurs in many biological systems such as during photosynthesis and respiration. Most of what goes on in the universe (e.g., collapsing and exploding of stars, biological growth and decay, the operation of machines and computers) involves one form of energy being transformed into another (Science for all Americans, p. 50). In physics, the study of the transformation of energy focuses on electrical circuits changing electrical energy to light energy. Students will later explain the Law of Conservation of Energy as it relates to the efficiency (loss of heat) of a system. Energy transfer occurs in many biological systems such as during photosynthesis and respiration. Most of what goes on in the universe (e.g., collapsing and exploding of stars, biological growth and decay, the operation of machines and computers) involves one form of energy being transformed into another (Science for all Americans, p. 50). Additional Findings Heat energy itself is a surprisingly difficult idea for students, who thoroughly confound it with the idea of temperature. A great deal of work is required for students to make the distinction successfully, and the heat/temperature distinction may join the mass/weight, speed/acceleration, and power/energy distinctions that, for purposes of literacy, are not worth the extraordinary time to learn them (Benchmarks, p. 81) Units and formulas for kinetic and potential energy then are important for the semiquantitative understanding that we seek here (Benchmarks, p. 81). Teachers have to decide what constitutes a sufficient understanding of energy and its transformations and conservation. (Benchmarks, p. 82) Many high school students think that models are useful for visualizing ideas and for communication purposes. (NSDL maps on models) 42

13 Chemistry, Quarter 3, Unit 3.3 Energy Changes and Energy Relationships Including Chemical Reactions (20 days) According to: NSDL energy transformations: Students rarely think energy is measureable and quantifiable. Student s alternative conceptualizations of energy influence their interpretations of textbook representations of energy. They may believe that no energy remains at the end of a process but may say energy is not lost because an effect was caused during the process; for example, a weight was lifted. The idea of energy conservation seems counterintuitive to high school students who hold on to the everyday use of the energy, but teaching heat dissipation ideas as the same type as energy conservation ideas may help alleviate this difficulty. 43

14 Chemistry, Quarter 3, Unit 3.3 Energy Changes and Energy Relationships Including Chemical Reactions (20 days) 44