Developmental Lesson FC #1.6: Styrofoam Ball Ions (Part II), Model Kits and Bonding Teacher Notes and Materials

Transcription

1 Facet Cluster 1.6: Ways Atoms are Held Together Goal Facets: 02 The student understands that atoms form bonds by sharing, losing, or gaining electrons because the electrons are electronically attracted to each of the atom's protons within their nucleus. When atoms bond they are more stable (lower energy) than when they are apart. Bonding results in a full valence or outer set of electrons for each atom. 04 The student understands how to use the periodic table to predict common bonding types including unequal sharing of electrons; polar and nonpolar covalent, ionic, metallic. [The student understands that the different types of bonding as well as the unequal sharing of electrons.] Overview: This lesson utilizes ball- and- stick model kits and a new set of Styrofoam ions in an examination of bonding between atoms. The Styrofoam balls in this part represent Na +1, Ca +2, and Cl - 1 ions. Questions in this developmental lesson refer back to questions and conclusions from the FC 1.5 Styrofoam Ball Ions (Part I) lesson. Materials: Student handout Eight 2-3 styrofoam balls 16 wooden pegs; 10 Velcro circles; Ball and stick model kit marker Elmers multi- purpose glue construction paper (or some other thick paper) superglue Construction of models: Note: It is necessary to make a new set of Styrofoam ball ions for this lesson. The ions created in the lesson for Facet Cluster 1.5 will not work here. 1. Slice each Styrofoam ball in half. Use the Elmers glue to glue a thick piece of paper such as construction paper to each inside surface of the ball. Push a wooden peg into each side so that the halves can be re- attached (Figure 1).

2 Figure 1: Addition of wooden pegs to half of Styrofoam ball. 2. To prepare Na +1, attach the hook side of a Velcro patch to the outside of a Styrofoam sphere, so that the hooks are facing out. Later the Velcro will be used to attach different Styrofoam spheres together, with the hooked side of the Velcro representing part of the positive ions and the loops representing part of the negative ions. Then separate the halves and on the inside use a marker to draw a nucleus containing 11 positively charged protons surrounded by 10 core electrons (Figure 2). Neutrons do not need to be shown since they have no charge. Make 2 sodium ions. - Figure 2: Addition of valence and core electrons to Na model. 3. Using the same method described above construct a model for a calcium ion (20 protons, 18 core electrons, and 2 Velcro hook sides on the outside). Attach the Velcro patches on opposite sides so there is room for bonding later. Make 2 calcium ions.

3 4. Construct 4 chloride ions using the remaining 4 Styrofoam balls (17 protons, 10 core electrons, and 1 Velcro loop side only patch on the outside). 5. Using the ball and stick model kit, construct the following molecules: H2O, CH4, NH3, and Cl2. Activity: In this activity, the Styrofoam balls represent ions and the balls from the model kit represent atoms. Each hooked Velcro patch represents a +1 charge on the ion and each looped Velcro path represent a - 1 charge on the ion. Therefore, since the balls from the model kit do not have Velcro patches, they are not charged. 1. Examine the Na, Ca, and Cl Styrofoam ball ions to see which ones stick together. Place an X in each box representing if the ions were able to stick together: Na +1 Ca +2 Cl - Na +1 Ca +2 Cl - What must be true in order for ions to stick together? 2. Take the 4 balls representing sodium and chloride ions and stick them together such that no Velcro patches remain without a partner. What is the chemical formula for each compound formed? What is the total charge on each compound formed? Hint: As in the Styrofoam Ball Ion Lesson from FC 1.5, the total number of protons and electrons in each ion can be counted by separating the halves. 3. Take the 6 balls representing the calcium and chloride ions and stick them together such that no Velcro patches remain without a partner. What is the chemical formula for each compound formed? What is the total charge on each compound formed? 4. In these examples with Styrofoam ions, ions that stick together are said to have formed an ionic bond. In Part I, you learned that ions are formed when atoms gain or lose valence electrons to result in a completely filled or empty outermost energy level. For example, sodium lost a valence electron to become positively charged and chlorine gained an electron to become negatively charged. Based on this, which

4 electrons participate in the formation of ionic bonds? What causes the ions to stick together? 5. Now let s look at the OTHER kind of model where we use balls for atoms and sticks to represent electron pairs. Examine the ball and stick model of Cl2. The balls represent neutral chlorine atoms and the stick represents 2 electrons forming an electron pair. Given your result from question #1 when you tried to stick two chloride ions together, do you think the bond joining the two chlorine atoms in the ball and stick model is different or the same as the bond joining sodium and chloride ions? Why? 6. Examine the neutral chlorine atoms constructed from Styrofoam balls that show the valence electrons. If these two atoms are joined by a bond as shown in the ball and stick model, what can you say about the outermost energy levels of each atom after bond formation? 7. Compare the atoms that form ionic bonds with those that form covalent bonds. Can you see any trends in the atoms that participate in ionic bonds versus covalent bonds? HINT: Look at the location of the atoms on the Periodic Table. 8. What is it about the ball- and- stick model that indicates that you built it correctly? 9. What do the holes represent? What do the sticks represent? 10. Describe how the Styrofoam Ion model and the Ball- and- stick model could be improved to give a better representation of atoms, ions and bonding.

5 Teacher Notes: 1. These models can be built ahead of time by the teacher or by the students in class or at home. The teacher may want to cut the Styrofoam balls in half and give these to the students to take home to build. Cutting the balls in half is the only potentially dangerous part of the construction. 2. One- gallon Ziploc bags are good for storage of the pieces so these models can be used many times. 3. Atoms could also be made from PlayDoh. 4. Remind students that the Ball- and- stick models are for COVALENT compounds only. The Styrofoam balls are for IONIC compounds. 5. It is recommended that you color code the atoms such that those used in Facet Cluster 1.5 are easily distinguished from those used in Facet Cluster 1.6 because the two sets of atoms are not interchangeable between these activities. Two suggestions are to use a different color of Velcro for each set or a different color of Styrofoam balls. This will prevent the two sets from getting mixed up.