Build an Atom

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SWBAT use the properties of subatomic particles to determine the properties of an atom based upon the number of each type of particle.

Big Idea

Using computer simulations to build our understanding of the atom.


This lesson is the first to begin to truly address HS PS1-1:  Using the periodic table as a model to predict properties of elements based on the patterns of electrons in the outermost energy level of atoms.  This is the first NGSS Performance Expectation that asks students to use the periodic table, and this activity begins to introduce them to the format of individual cells of the periodic table, and how protons are related to atomic number and identity of elements.

Students will engage this after learning about the discoveries of the electron and the nucleus, but likely with an incomplete visual model of the atom.  Our emphasis today is on Science and Engineering Practice 2, Using models.  Our model of choice is a computer model provided by the PhET project at the University of Colorado Boulder.  This is a free online simulation it that I use a lot throughout the year to provide clear visuals for students.  It does require Java, so it may not be accessible in all locations.  However, this particular simulation is also available via HTML5, and runs on tablets, netbooks and smartphone browsers.

We also will be tapping into Science and Engineering Practice 4, Analyzing and interpreting data, as students will decide which particles to add in each trial, and record what is changing to determine the properties of each subatomic particle.  From their data, they will use Science and Engineering Practice 6 and construct an explanation from their simulation results -- both individually and together in small groups.

This lesson is designed for 42 minutes.  My district does department meetings each Wednesday morning, and our classes are shortened as a result.  If you had extra time, I would recommend spending it on the simulation game with students.  Don't have the students exit the computers before the debrief so they are ready to go, and return to the computers after the debrief to play a couple round of the game for five minutes, and give an extra three minutes to the exit ticket.


5 minutes

As students enter, the direction "Draw an atom on a piece of paper" is on the board.  When the bell rings, I ask students to find a blank page in their binders and complete the activity while I take attendance.

Once attendance is done, I circulate the room inspecting their drawings. In previous lessons (linked here) we have "discovered" the positive nucleus and the presence of negative electrons already, so I am expecting students' drawings to represent a nucleus with electrons orbiting it.  Some students may represent both protons and neutrons from our vocabulary work, and most advanced students will have equal numbers of all particles.

I select a few drawings to share via the document camera and we discuss the strengths of each model, and what evidence we've learned for each piece so far.  I ask explicit questions to link their models with our experiments with charges, Thomson's cathode ray experiment, and Rutherford's Gold foil experiment.  For instance, "How do you know there's a nucleus?" or "Why did you draw the electrons as minus signs?"

I then tell the class today we will be using the computers to build upon and enhance our understanding of the atom's structure.  I ask students to go back with their partners and log into the computers.  Our system often takes up to three minutes to log in, so this provides a transitional time.

Computer Simulation

20 minutes

While students are logging into the computers, I distribute the Build an Atom Simulation worksheet and help cards.  Once all students are logged in and have a sheet, I use the projector to demonstrate the simulation (HTML5 version) for them and we all do the first row of the worksheet together as seen in this screencapture.  I add 3 protons to the atom and ask the students what changes occur.  They note:

  • The symbol is Li+3
  • The mass number is 3
  • The net charge is +3
  • It is shaking and unstable


We record each observation in the correct column.  I then show them how to reset the simulation.  I instruct them to then try different combinations of particles in the space provided, resetting each time.  I show them how when they reset they need to re-open the Symbol, Mass, and Charge tabs before beginning.  I remind them to flip their help cards to red if they get stuck.

I then let them experiment for about 15 minutes and discuss what they are observing.  If students gather data quickly, I let them try the game, which presents them with numbers of particles and asks them to identify the element.  This is a backwards application of what they did, and is a good gauge of how well they understood and connected presence of particles with their individual properties.  At the end of the time, I send them to the front of the room.


17 minutes

When students return to their tables, I give them seven minutes to write out their summary at the bottom.  When a table is complete with their summary, I assign them one of the terms from the summary to write down everything they know about it on the front white board.

I can differentiate for success here by assigning tables that had solid information about the more complex ideas those terms, such as ions, atomic mass or net charge.  This allows me to give a table who might be at a more basic understanding the terms we have been working with for a period of time.

After a total of 10 minutes have passed (seven for individual summary, three for whiteboard recording), I review each term with the class, reinforcing correct material and challenging misconceptions (such as ions being only positive or negative).  I remind students to be certain that their papers represent the final, correct information on the board at the end of the discussion.