POGIL EXERCISE 15 Why and How Do Atoms React with Each Other?

Transcription

1 RUN TIME: 65 MIN POGIL 15 Page 1 of 8 POGIL EXERCISE 15 Why and How Do Atoms React with Each Other? Each member should assume his or her role at this time. The new manager takes charge of the POGIL folder and hands out the GRF and RRF to the appropriate members. The new recorder should record the names of the group members on the new GRF. Table 1. Group Member Role Assignments GROUP TYPE -> GROUPS OF THREE GROUPS OF FOUR MEMBER NO. -> Manager + + Reporter + + Recorder + + Reflector + + Technician Encourager + + SFUC + * + * INTRODUCTION. Here is what you need to remember from previous lesions: (1) Electrons are the subatomic particles that determine the chemical reactivity of the atom. (2) Electrons of an atom are arranged around its nucleus in a specific pattern of energy levels. (3) The valence electrons (outer most s and p subshells) are the electrons that have the most effect on the reactivity of the atom. These valence electrons are responsible for the chemical reactivity of the element and this relationship makes chemical bond formation very predictable. (4) The other electrons of the atom are called core electrons and play only a minor role in determining the chemical reactivity of the element. 1. As a group, write on the back of this page the name, the noble gas electron configuration and Lewis diagram for the Period 6 elements having the following atomic numbers: 55, 56, 57, 67, 79, 82, 84, 85, Which four elements are main group elements? 3. Which element(s) are d-elements? 4. Which element(s) are f-elements? +10 MIN

2 RUN TIME: 65 MIN POGIL 15 Page 2 of 8 5. What is the relationship of the number of dots in the Lewis diagram of each element to the element s electron configuration? 6. What is unique about the electron configuration of element 86? OBSERVATION I. In this lesson we will learn some general principles that will guide us in our understanding of how and why atoms react with each other. The first and perhaps most important is this statement: Atoms will react with each other by donating, accepting, or sharing electrons so that each atom in the compound achieves a noble gas electron configuration. This concept was named by Gilbert Lewis as the octet rule (or Rule of Eight). This rule has been immensely valuable to understanding basic chemical bonding between the elements because it explains so many observations made by chemists over the years. We will begin our understanding of this rule by looking at the reaction of sodium and chlorine diagramed in Figure 1 below. Figure 1. Lewis Structure Representation of the Reaction of Sodium and Chlorine. 7. Keep an eye on the dots as you go from left to right in Figure 1. a. How many dots are there on the left and right of the reaction arrow? b. What happened to the dot seen in metallic sodium in Figure 1? 8. Write the complete electron configuration of Na: 9. Write the complete electron configuration of the sodium ion (Na + ): 10. What was the designation of the electron lost to create the sodium ion? 11. What noble gas has the same electron configuration as Na +? 12. Does the sodium ion conform to the octet rule? Justify your answer. 13. Write the complete electron configuration of Cl: +20 MIN

3 RUN TIME: 65 MIN POGIL 15 Page 3 of Write the complete electron configuration of the chloride ion (Cl - ): 15. What is the designation of the electron gained to create the chloride ion? 16. What noble gas has the same electron configuration as Cl -? 17. Does the chloride ion conform to the octet rule? Justify your answer. Present your answers to the instructor for validation. The group should take a FULL minute to study Figure 2 including counting the dots. Figure 2. Lewis Structure Representation of the Reaction of Hydrogen and Nitrogen. 18. Is the number of dots on the right and left of the reaction arrow equal? 19. What happens to the electron on hydrogen? 20. Do all atoms in the product (ammonia; NH 3 ) conform to the octet rule? Explain your answer for each element. 21. Was the method by which the nitrogen and hydrogen atoms in Figure 2 achieved the noble gas state the same as the sodium and chlorine atoms of Figure 1? Explain your answer. OBSERVATION II: The reaction of magnesium with chlorine occurs according Equation 1. This equation also shows what happens when the product, magnesium H 2 O EQ1: Mg(s) + Cl 2 (g) Mg Cl - Chloride. Since MgCl 2 is composed of a metal and nonmetal element, it is an ionic compound; most ionic compounds like MgCl 2 undergo ionization when placed in water. +30 MIN

4 RUN TIME: 65 MIN POGIL 15 Page 4 of Using the information and knowledge gained so far, draw a Lewis representation of the reaction similar to Figure 1 or Figure 3 as described by Equation 1. Figure 3. Lewis Representation of the Reaction between Magnesium and Chlorine. Recorders should present the group s reaction to the instructor for validation. Continue as specified by the instructor. 23. Which Figure (1 or 2) does Figure 3 resemble? Explain your answer. OBSERVATION III. Equation 2 describes the reaction that occurs between oxygen and hydrogen. The product, water, is composed of two nonmetal elements; therefore, it does not spontaneously break apart indicating the bond formed is a covalent bond. EQ2: 2 H 2 (g) (g) 2 H 2 O(g) 24. Using the information and knowledge gained so far, draw a Lewis representation of Equation 2 as Figure 4 below. Figure 4. Lewis Representation of the Reaction between Hydrogen and Oxygen. Recorders should present the group s reaction to the instructor for validation. Continue as specified by the instructor. 25. Which Figure (1 or 2) does Figure 4 resemble? Explain your answer. OBSERVATION IV. There are two basic types of strong bonds formed by chemical reactions. Ionic bonds are formed when electrons are given up or accepted by atoms to achieve the noble gas state. This transforms each atom into an ion (a charged atom). The bond is generated by the attraction of the cations (positive charges) and the anions +40 MIN

5 RUN TIME: 65 MIN POGIL 15 Page 5 of 8 (negative charges). Compounds formed in this manner are known as ionic compounds. In the absence of water, the ionic bond is very strong. However, when these compounds are placed in water, the water molecules surround the ions insulating the attraction between the positive and negative components. Due to kinetic energy the ions simply drift away into a sea of other water molecules and the solid disappears and is said to be dissolved. The process by which an ionic compound breaks up into its ions in water is called ionization. Covalent bonds are formed when the elements share electrons to achieve their noble gas states. These bonds are weaker than the ionic bonds but are stable in an aqueous environment. Most organic molecules have covalent backbones. There are two types of covalent bonds. When the sharing of the electrons is equal, each electron spends the same amount of time around each of the elements so that every part of the molecule has the same partial charge. This type of covalent bond is called a nonpolar covalent bond. When the electrons are shared unequally a partial charge is generated on different parts of the molecule because the electrons spend more time around one nucleus and less time around the partner nucleus. This type of covalent bond is called polar covalent bond. Ionic compounds tend to fall apart (ionize) when place in water. On the other hand, most covalent compounds are extremely stable in an aqueous environment. 26. Based on the definitions in Observation IV, classify the types of bonds formed in Figure 1-4 by completing Table In the space below or on the back of this sheet, draw a diagram of what happens when CaCl 2, a soluble ionic compound, is added to water. +50 MIN

6 RUN TIME: 65 MIN POGIL 15 Page 6 of 8 Table 2. Classification of Reactions in Figures 1-4. Figure No. Type of Compound Formed Type of Chemical Bond How Bond Was Formed 1 ionic Ionic Electrons were donated by sodium atom and accepted by the chlorine atom OBSERVATION V: Perhaps you re wondering why some of the reactions form ionic bonds while another set of reactants form another type of bond. Well, the answer is in the atomic property called electronegativity. Electronegativity is the potential of the atom to gain electron(s). This property increases from Group 1 to Group 7 elements and from Period 6 to Period 1 elements (Table 3). The type of bond after the two elements react can be predicted from the absolute value of the difference in their electronegativity (Table 3). Process Items in Table 3 on the next page using information in Observation V and Table MIN

7 RUN TIME: 65 MIN POGIL 15 Page 7 of Which element has the lowest electronegativity? 29. Which element has the highest electronegativity? 30. What group of elements has essentially zero electronegativity and thus zero chemical activity? 31. What type of compound will be formed if an element from Group I reacts with an element in Group VII? 32. Suppose you were using a regular periodic chart instead of a table like Table 3. What generalization can be made about the relative position that two elements to each other and the type of chemical bond formed? The Recorder should present the group s answers to Items For each row of Table 4, locate the elements in the first column on a periodic chart. Using their relative positions only a periodic chart and the information in Observation IV, predict the type of bond between the two elements. Place your dictions in Cells 1-3 of Table 4. Table 4. Chemical Bonding and Electronegativity BOND ESTIMATE FROM PERIODIC CHART Li Cl BOND DETERMINED WITH AID OF TABLE 3 P21 H C C F MIN

8 RUN TIME: 65 MIN POGIL 15 Page 8 of 8 Ask the instructor to validate your responses. 34. Using only the information in Observation 5 and Table 3, calculate the absolute value of the difference of the electronegativity between the two elements, place that value in Boxes 4-6 (Column 3) of Table 4. Determine the type of chemical bond by using this value and the scale on the right column of Table 3. Enter this determination in Table 4, Column Compare your responses in Columns 2 and 3 of Table 4. What percent of the three pairs agree with each other? 36. What can you conclude about the accuracy of the placement of the elements in a periodic chart versus the calculation of the difference using a table like Table 3? Before packing up discuss you findings recorded in Items with the instructor. EXERCISE END. Managers should collect the GRF and RRF, staple them together, and place in the back of the left pocket of the folder. Recorders may keep their session for study for the test. The folder should be closed and left on the table. +65 MIN