Electron Orbital Diagrams
Lesson 2 of 9
Objective: SWBAT complete electron orbital diagrams (using boxes and arrows) following Aufbau Principle, Hund's Rule, and the Pauli Exclusion Principle.
This lesson helps students understand the various energy levels of electrons and further reinforces work in explaining why different elements want to gain or lose electrons to gain stability. This understanding is necessary for students to be able to address both Performance Expectations HS-PS1-1 and HS-PS1-2.
Students who are planning to enter college for a STEM field will be required to take a first year chemistry course in which electron configuration will be covered at a deeper level. A general understanding of this concept will help prepare students for future chemistry work. In addition, students who struggled with determining electron configurations have a chance to re-learn that concept within the framing of electron orbital diagrams. Students will use the box and arrow model for showing electron patterns, addressing SP2 - Designing and using models.
This lesson is structured to help students identify patterns in the Periodic Table so that they are not simply memorizing and are instead using the Periodic Table as a tool that they understand. This strategy is part of the Next Generation Science Standards Crosscutting Concepts, addressing Patterns. Particularly, Crosscutting Concept XC-P-HS-1 is directly addressed as students look for patterns in electron configuration to later explain bonding phenomena.
While I take attendance, students do a warm-up activity in their composition Warm-Up/Reflection books. I use warm-ups to either probe for students' prior knowledge about the day's upcoming lesson or to have them bring to mind and review what they should have learned during the Flipped Classroom Lesson recording the night before. (To read more about Warm Up and Reflection Books, please see the attached resource.)
Today's Warm-Up: "What do the arrows represent in an electron orbital diagram?"
In this case, the warm-up is asking students to call upon information they would have gained had they watched the assigned video as homework. The video is attached here:
Today, I walk around to spot check who has the answer written down rather quickly and independently. This is a relatively good indicator of who watched the video, as I clearly and explicitly state in the video that the arrows in an electron orbital diagram represent electrons. Students who did not watch the video will struggle with answering because we have not discussed electron orbital diagrams in class as of yet.
While I would typically stamp books for warm-up answers, today I do not because the warm-up prompt itself is not asking for any deeper thinking or analysis on the student's behalf that might warrant further discussion. This prompt is simple recall.
I ask students if anyone cares to share what their answer was, and call on one student once there are at least 5 hands in the air. After that student answers, I ask if anyone would like to confirm it as correct or if there is another answer. This way I allow students to correct themselves and each other, rather than constantly seeking answers or confirmation from me.
I explain to students that electron orbital diagramming, as they saw in the previous night's homework video, is based on electron configuration notation, which they already understand. I reiterate the information contained in the video, pausing to ask students to give answers that they may remember from the video lecture.
The information I am primarily looking for is:
- Electrons are represented with arrows, pointing either up or down
- As electrons fill sublevels, they pair up--one arrow up and one arrow down
- Each individual orbital holds up to 2 electrons
- Electrons spread out within a sublevel before they begin to pair
- Electrons fill lowest energy levels first
We do a couple of elements as examples (I like to use nitrogen and sodium) on the whiteboard. I reiterate that the boxes must be labeled.
Small Group Work
I pass out to students the Orbital Diagrams handout (here is the KEY). I allow students to work in small groups (2-3 students) to complete the task and check with each other. This builds cooperation and allows students with deeper understanding to help their peers who are perhaps not at the same level of understanding. While students work, I walk around to help any students who call me over and to listen in to student discussions, interjecting if there is a group that is way off base in their understanding. I also provide reassurance and praise to groups who are on track by offering words of affirmation (i.e. "You really seem to understand this well").
Things I am looking for as I walk around:
- Labeling of the orbital boxes - Students need to add the 1s, 2s, 2p, etc. orbital labels
- Adding of electron arrows starting at the lowest energy level - Students should start at 1s and move in order to 2s, 2p, 3s, 3p, and 4s according to the Aufbau Principle
- Arrows should be added as arrow up first, then, if paired, arrow down - Students should not have two arrows pointed up or two arrows pointed down in the same box according to the Pauli Exclusion Principle
- Electrons should be spread out among orbitals of the same energy level (i.e. the three 2p orbital boxes) BEFORE pairing up - Students should not pair electrons until all three of the 2p orbitals each have one according to Hund's Rule
I am also looking to see if students are taking the atomic number from the periodic table for each element correctly, and correlating that to the number of electrons to include in the orbital diagram.
Most students did very well with this assignment and this was a chance to reinforce quantum electron configurations as well. This student sample is typical of what I collected. The students who understood electron configurations the first time around did not typically label the orbitals (1s, 2s, 2p, etc.) as the assignment directs, but their electron configurations were correct.
Only a few of my students had true difficulty in completing the assignment correctly. This student in particular could not complete the diagrams or the electron configurations correctly, partially because she had been absent for several days prior to this lesson and had missed learning quantum electron configurations.
Students were also able to construct their own orbital diagrams by drawing their own boxes and labeling the orbitals, as shown here:
Whole Class Discussion
Once students have had enough time to finish the handout (approximately 30 minutes), I ask students to return to their tables so that we can discuss the answers and to make sure we understand how orbital diagrams and electron configurations are related to each other. I use this opportunity to have students correct each other's work so that we are discussing answers right away and I have graded papers that can be entered into the gradebook immediately.
I use an LCD projector and a document camera to solve the worksheet with student participation in the discussion. I might begin, "How many electrons does aluminum have?" since that is the first element on the handout. Then I'd ask, "Do I need to add any labels?" to prompt students to tell me to add 1s, 2s, 2p, and 3s to the diagram. I'd work through this example counting out loud the electrons (arrows) as I add them, modeling each time I fill in a p-orbital that they spread out among all three p-orbital boxes first, then pair up (even on a completely filled p-orbital).
As I go through the problems, I ask students to mark anything that needs to be corrected on their partners paper. I always ask students to use a different color pen and/or pencil than their partner completed the work using so there is clear delineation between what was completed correctly to begin with and what needed correction.
Once we are done, I collect the papers for final grading and entering, telling students that they will receive their papers back the next class period.
Today, in order to build the connections between electron configuration and orbital diagrams, the reflection prompt asks students to explain what relationship they see between these two concepts.
Today's Reflection Prompt: "Name one similarity and one difference between an element's electron configuration and its electron orbital diagram."
By asking this question, I am hoping to prompt students to realize that both electron configuration and orbital diagramming tells us an element's number of electrons and those electrons' energy levels. They both also indicate how many more (or less) electrons an element needs to be more stable. The key difference between them, however, is that orbital diagramming gives us more information about individual electron behavior which leads to greater understandings of interesting elements (like transition metals' d-orbital behavior, which we briefly discussed in class).
Here are two typical student reflection responses. The first answer is more surface-level while the second answer goes a little deeper in explaining the difference.