In this lesson students will work with atom modeling kits and a data table to model how atoms gain or lose electrons in the valence shell in order to acquire a full outer shell. Students have some prior knowledge on this subject because they participated in this lesson. However, this is an important and somewhat complex subject and so I chose to spend more than one lesson on the material. In this lesson I expect students to think more than the last lesson. I was more supportive with answers to their questions in the last lesson, but in this one I expect them to do more thinking.
This lesson aligns to the NGSS Disciplinary Core Idea of Matter and Its Interactions because students use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms. In this case they are predicting how many electrons are gained or lost based on the number of valence electrons an atom has in its valence shell.
It aligns to the NGSS Practice of the Scientist of Developing and using models because while students cannot physically manipulate valence electrons at the atomic level they can model how atoms gain a full valence shell through gaining or losing electrons.
It aligns to the NGSS Crosscutting Concept of Structure and Function. Specifically it aligns to this concept by showing how the functions and properties of natural objects can be inferred from their overall structure. The natural objects are atoms, the property is reactivity through the loss or gain of electrons, and the structure is the valence shell.
The materials needed for this lesson include the following:
Do Now: When students enter class today they are asked to pick up two handouts, the Directions for Modeling how an Atom Becomes an Ion and How atoms become ions practice problems. I ask them to look at the two documents and record the questions they raise.
I have chosen this approach because I am under the impression that students have only a superficial understanding of how atoms gain a full outer shell. I want to see how much they are thinking about their work, and how much they are focused on what the book and lecture notes are saying about the subject.
Activator: After I have taken attendance I ask students to ask their questions. Students do not have any! While this is frustrating, it does reinforce my perception that they are not thinking enough about the topic. When I ask for volunteers to model how atoms get a full outer shell, I get no takers.
My reasoning behind choosing this approach to how class starts is that I am trying to make a bit of a point in class today, namely that students have to think about their work in order to come to an understanding about what is happening.
Mini-lesson: I briefly discuss each of the columns in practice problems handout. For column 2 I note that they should use the order of electron filling that they learned in this lesson and the atom modeling kit. For column 3 I remind them that they can use the periodic table's A group numbers or add up the subscripts from the outer shell to determine the number of valence electrons. For column 4 I remind them that when an atom has less than 4 valence electrons it is easier to lose electrons, and when it has more than 4 it is easier to gain them. I note that for column 5 atoms lose all their valence electrons when they are losing, and gain enough electrons to fill the outer shell. I also note that the ion's electron configuration should show a full outer shell. In keeping with trying to connect previous classes to the current one, I also asked students to add two columns not on the original worksheet for Lewis dot structures.
I do not spend a lot of time on this mini-lesson. My rationale is that I want to emphasize to students that while I may say something, and it may make sense to them in the moment, the only way to really learn something is to make meaning out of it by doing something with it.
Guided Practice: I ask students to do the first practice problem, and then we review the problem as a class. Students vary widely in their understanding of what is being asked in different columns. Some students do not understand how to draw Lewis dot structures, a few have still not learned the order of orbital filling, and some are still getting confused about how the gain or loss of electrons affects charge.
I am pleased with my read of the students' mastery of this material. My expectation is that after this lesson students will be much farther along, and this will make the upcoming bonding lessons much more understandable.
Student Activity: During this time students grapple with their understanding of the content by completing the practice problems found in the worksheet How Atoms Become Ions. I encourage students to use the atom model with its clearly defined orbitals because it can help students to visualize what is otherwise an abstract idea.
Different students have different strengths. A few have mastered the material and I encourage them to help other students. In general, this culture is starting to form in the classroom. In this video called Discovering the duet rule you can see how giving students the opportunity to grapple together can lead to students forming their own questions and understanding when I am called in to settle a dispute about whether boron is more likely to gain or lose electrons. While my initial reaction is to say "what is the most electrons boron can have?" and I wondered afterwards why I said that, the clip is a good example of how to use questioning to help students discover the answer they are seeking.
Interestingly, this video in which I use questioning to help a student think deals with the same topic of how boron gets to a full outer shell. In this video, however, the thing I want to emphasize is my insistence that students use their notes to assist them in understanding today's lesson.
Catch and Release Opportunities: On a couple of occasions students can show their work using a document projector. I do this because it cuts down on the amount of times I hear the question "Is this right?" My main foci as I walk around the room while students are working are making sure my instruction was sound, and answering questions that lead to an increase in student understanding. While checking to see if the work is right can help students feel more confident, having students feel confident because they figured it out for themselves is an even greater confidence boost.
To wrap this lesson up I use cold call to ask students to explain how the answer to each column is derived.
For column 2 students know they should use the order of electron filling.
For column 3 students explain that they can use the periodic table's A group numbers or add up the subscripts from the outer shell
For column 4 students note that when an atom has less than 4 valence electrons it is easier to lose electrons, and when it has more than 4 it is easier to gain them.
For column 5 students explain that atoms lose all their valence electrons when they are losing, and gain enough electrons to fill the outer shell. There is still a little confusion about the charge of the ion, so I remind them (again!) that when an atom loses electrons it is losing a negative particle and so the there are now more protons than electrons and so even though the atom is losing, the charge becomes more positive.
For the Lewis dot structures students note that the valence is unfilled on a neutral atom and filled on an ion.
Judging from this characteristic student work my students still need to work on this skill. While the electron configurations for the ions seem to be correct, some of the electron cloud models are off. For example, P has 2 electrons in the outer shell for the ion. I will need to reemphasize why atoms are gaining or losing electrons, namely to have a full outer shell, at a subsequent time.