Star Crossed Charges pt 2

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SWBAT interpret models in terms of how the number of charges and distance between opposite charges affect attractive forces

Big Idea

Paper models help students understand Coulombic attraction between subatomic particles.



8 minutes

I begin class by asking students to write a complete sentence explaining the relationship between the distance between charges and the strength of their attractive force.  I am hoping for "As the distance between forces increases, the attractive force decreases".  Student responses include:

  • As force changes, so does distance
  • As the distance changes, the force decreases
  • As the charges increase, the force decreases
  • Nothing

From this, I quickly realized the issue is that students don't know how to explain relationships in clear language.  I ask them to instead write down the relationship between the amount of sleep they get at night, and how tired they feel the next day.  Sample responses include:

  • The more I sleep, the less tired I am
  • The less I sleep, the more tired I am
  • If I sleep a lot, I'm not tired the next day.

I ask them to compare how they wrote the sleep relationships with how they wrote the distance relationships and tell me why the sleep relationship statements are better.  Many students note that they said how both sleep and tiredness changed, not just that they did.  I point out that indicating the direction of change is crucial to our statements, and we write a class statement for distance and strength of attraction before moving to independent work.

Independent (?) Work

30 minutes

After reviewing Models 1 & 2, I get students working on the remainder of the packet, beginning with Model 3. Model 3 shows four different trials, with the charges at equal distances of .10 nm, but each time with an additional positive charge, or proton represented.  Students should see that with the addition of each proton, the attractive force increases by the same amount each time.

As this is our first experience with POGIL, I will give them the option to work alone or in a pair.  Later in the year, I will have them work alone, but due to the new procedure, I'd rather they work in a mode that is safe for them to grow. As each table transitions to the independent/paired work, I circulate the room and answer questions, provide feedback, ask clarifying questions, and act as cheerleader.

If they select to work in pairs, I send one pair back to a lab table with a help card, with the other pair remaining at the front student table with a help card.  I remind them to ask questions if they can't figure out a direction, and to check in with me when they reach a stop sign

When they reach the stop sign, I check their conclusions and evidence, ensuring that they understand that each additional charge increases the attraction by a set amount before turning them loose on Model 4, which looks at attraction across a period.  I modified this from the original to show the number of protons in the nucleus of each atom, as we have not yet worked with the periodic table.

When students finish, I ask them to return to the front of the room.  I use the Online Stopwatch on the overhead to indicate when they need to be complete so that we can debrief.

We will utilize some of the POGIL diagrams on our unit exam, so it is important they feel comfortable with the models and can interpret the structured questions independently.

Sharing and Debriefing

12 minutes

For the debrief, I ask each table to check with each other, and organize a definitive statement explaining the relationships they discovered in Models 3 & 4.  I refer them back to our relationship statement discussion at the start of the period as an example.

After 4 minutes, and circulating the room, I give each table two index cards.  I have them record their statement for Model 3 on one card, and Model 4 on the other card. 

I have the tables pass their cards one table to the right, and to read and give any feedback they want on the statements.  I give them 4 minutes to provide feedback/critiques of each other.

I then have the students pass the card back to the original table.  I ask the students to look at the feedback they received, and think about the feedback they gave.  Then they flip the card and write a "Final Relationship Statement" on the back of the card, and put everyone's name on it.

As students exit the room, I collect the cards as an exit ticket.

Due to the talk at the start of the period, the initial relationship statements for model 3 were fairly good, indicating that increased number of charges increases the attractive force.  Student feedback refined these some, as some groups used the exact amount of change per proton as represented in the model.

The model 4 statements were a little rougher, as students had a hard time applying this to the atom due to still having uncertainty about the structure of the atom.  Students indicated that more protons in the middle increased the attractive force on the outside, but many students are still swapping the electrons and neutrons positions in the atom.  This was caught by groups in the feedback stage, so the final statements were much improved and more accurate.