Summary
As a prerequisite, students should already be familiar with determining an element's electron configuration.
Essential Question(s)
How are valence electrons counted and visually represented?
Snapshot
Engage
Students participate in an Always, Sometimes, or Never True formative assessment about electrons.
Explore
In small groups, students complete a card sort to discover relationships among electron configuration, valence electrons, and Lewis dot structures.
Explain
Students gain clarity on electron-specific terminology and understand conventions for identifying and representing valence electrons.
Extend
Students practice determining numbers of valence electrons and drawing Lewis dot configurations for various main group elements.
Evaluate
Students reflect on their learning and provide the electron configuration and Lewis dot structure for a self-selected element on the periodic table.
Materials
Periodic table handouts
Card sort sets
Lesson slides
Engage
Go to slide 5. Begin the lesson by having students participate in an Always, Sometimes, or Never True formative assessment exercise. Facilitate this as it works best for your class, for example: completed individually on paper, having students hold up index cards with always, sometimes, or never written on them, class voting, etc. It is not necessary to review the answers with the students at this point since it is just for your reference.
Explore
Next, students will work together to complete a Card Sort. Divide the class into six groups and give each group one set of cards. Together the cards contain the first 20 elements of the periodic table, distributed across all six sets of cards. There are duplicates of some elements but never in the same set. Each element card includes its full electron configuration to aid students in drawing conclusions throughout this activity.
Go to slide 6. Within their groups students should match up each of their five element cards with their corresponding Bohr model and Lewis dot structure. After completing the sort, give each group some time to look for patterns between where their elements are located on the periodic table and the information they used to match the cards. Go to slide 7. Now have the groups pair up so you end up with 3 large groups. In the expanded groups, students should work together to identify these same periodic table/card patterns among all 10 elements they now have. Once the three groups have had time to draw conclusions about the patterns they identified, bring the class back together to discuss their conclusions.
Before moving on, go to slide 9 and ask students to conclude what is (1) the maximum number of electrons that can be shown in the dot structures and (2) the maximum number of electrons that can be found in the outer ring of the Bohr models for these elements specifically. (The relevant relationship here only works for the first 3 energy levels, after which the d and f orbitals can hold >8.) Tell them at this point that those eight electrons (or two in the case of Helium), are the element’s valence electrons. Be sure to collect the card sort cards before moving on to the rest of the lesson.
Explain
Go to slides 10-12 and walk students through the details about shells, subshells, and orbitals. Continue to slide 13 to describe orbital geometry. Students are not expected to remember any details about the shapes of orbitals; the images are provided to support the concept that having more electrons results in more complicated orbits as they repel one another.
Continue to slide 14, which focuses specifically on the p-subshell to provide an example of where the numbers come from in electron configuration. The slide is animated to show:
the spatial relationship among the three p-orbitals,
that we can think about p6 as adding two electrons from each of the three orbitals, and
that p6 could also be thought of as multiplying 3 (p-orbitals) times 2 (electrons).
Go to slide 15 which shows three annotated examples of partial electron configuration. Review the shell, subshell, and orbital summary on slide 16.
Go to slide 17 to introduce valence electron details. The slide is animated to show one bullet point at a time. As you cover the information, ask students to reflect back on their card sort to provide explanations for how they know what number of valence electrons are in each group and why there are 8 valence electrons/where that number comes from (“s2 + p6 = 8 electrons”). Continue to slides 18-19 to explain Lewis dot structures and how to draw them. Be sure to edit the 3rd bullet point on slide 19 if you have a specific convention for where you want students to begin drawing.
Extend
After completing the Explain, provide each student with a copy of the Extend Practice Problems handout. This can be completed individually or in small groups. Go to slide 20. Give students some time to complete all ten elements and then review the answers as a class. Go to slides 21-22. Rather than just providing answers and moving on, be sure to ask students to explain their reasoning throughout the discussion:
How did they determine the element’s group number?
How did they know the number of valence electrons?
How did they draw their Lewis dot structure (describe their process)?
Evaluate
Cut the Evaluate Activity and Reflection handout in half and give one to each student. Go to slide 23. Provide students with the following list of elements and ask them to select one to complete the activity.
As - Arsenic
Ba - Barium
Ga - Gallium
I - Iodine
Pb - Lead
K - Potassium
Se - Selenium
After completing the Lewis dot structure assessment portion, students will complete a What Did I Learn Today? reflection on the same sheet.
Resources
Always, Sometimes, or Never True https://learn.k20center.ou.edu/strategy/145
Window Notes https://learn.k20center.ou.edu/strategy/189
What Did I Learn Today? https://learn.k20center.ou.edu/strategy/169