Modeling the Atomic Structure

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SWBAT differentiate between the sub atomic particles in an atom in terms of charge and location.

Big Idea

Students model the structure of an atom using an guided inquiry investigation.


This lesson addresses the NGSS HS-PS1-1, "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".  The goal of the lesson is to introduce students to the basic structure of the atom, its subatomic parts, their charges and the relative size of the atom.  This is aligned with the NGSS Disciplinary Core Idea (DCI) PS1.A (Structure and Properties of Matter): “each atom has a charged substructure consisting of a nucleus, which is made of protons and neutrons, surrounded by electrons”. 

The students explore the atom using the NGSS Practices of Questioning and Modeling.  This is the second stage of questioning that students are practicing.  The goal is to guide students to ask higher-order questions and build confidence in questioning. Students will are not expected to master questioning only after two days of exposure, but should start to develop a better understanding of the importance of asking higher-order questions.  Students will engage in the practices of modeling by using the PhET “Build an Atom” simulation.

The NGSS Cross Cutting Concept (CCC) that is illustrated throughout the lesson will be Scale, Proportion, and Quantity because “it is critical to recognize what is relevant at different measures of size, time, and energy and to recognize how changes in scale, proportion, or quantity affect a system’s structure or performance”. This CCC is an underlying theme and that students will not be summatively evaluated on this part of the lesson.  

Homework Discussion

10 minutes

At the beginning of class I take a few minutes to collect the final copy of the concept map that was completed as homework (Day 1: Parts of the Atom).  I then choose 2-3 students randomly (see reflection for participation techniques) and display their work on the document camera (ELMO) one at a time.  I ask the class to provide some comments about the concept map that is being displayed.  I do not allow the students to see the name on the concept map because at this point in the school year students are still uncomfortable with one another which can have negative consequences. 

The goal is to get students to analyze the variety of ways to explain the subatomic parts and size of the atom, and to show that no two students interpret information the same way.  While viewing each of the concept maps, students participate in a think-pair-share about each of the concept maps; this should only take about 2 minutes per concept map, just enough time for students to generate questions and engage in a brief discussion.

Next students share with the person to their left one day and the right on another day; this promotes discussing with different people.   Since the goal of the lesson is mastery of the atom, I show a version of the Atom concept map that I created, so students can revise their concept map (CM) for homework if they choose to do so.  

The areas that students show the most difficulty with is providing words that connect the main "concept words" with one another and finding a way to connect atomic number and mass # in a structured, coherent way.  These tend to be new concepts for students and will require further practice that will occur in later lesson.  Again, the whole point of this concept map is to get students to have information to scaffold to later information that will reinforce the concept. 


30 minutes

As students hand in their homework at the beginning of class they are also instructed to pick up a copy of the Build an Atom inquiry investigation (Build an atom key1 Build an atom key2). This investigation will be done in groups of two and requires access to a computer that can run a PhET (Java script) simulation. I provide a modified version of an investigation from the PhET site (because the simulation address ions which will be covered in a later lesson), but there are plenty of developed investigations on the site that can be used.  

I use groups of two because this investigation requires students to discuss and question what they are modeling from the simulation (NGSS Practice: Questioning and Modeling).  This exploration also allow students to elaborate on what they have learned about HS-PS1-1 (DCI PS1.A) in the previous lesson (Day 1: Parts of the Atom) by investigating how the number of protons can affect the type of atom, along with how protons and neutrons change the mass of the atom.  As a secondary concept, students will be exposed to how each subatomic part changes the net charge of an atom.

 The first part of the investigation asks students to take a few minutes to explore the simulation and write down a couple of questions and observations.  Earlier in the school year students were given a list of question stems to help generate questions.  

After about 5 minutes, I stop the class from going any further and have several groups share some of their preliminary questions and observations (see "Build an Atom key 2" resource one for examples of student questions).  This helps students collect their thoughts and allows struggling students the chance to get up to speed in terms of the simulation. 

After the brief discussion, the rest of the investigation is done without teacher interference.  The purpose of this is to get students comfortable with the idea that inquiry is about exploration, not dictation. The purpose of modeling the investigation is so students can build their own understanding and scaffold this information to future learning.  

Students should come out of this investigation with a reinforcement of where protons and neutrons are located, an introduction of how to calculate mass number, what protons represent in an atom, and where electrons, protons and neutrons are located.  

This PhET simulation proves to be an effective way to illustrate an atom, in addition it coincides with the NGSS practice of Modeling.  Students enjoy playing around with the simulation, and it does an excellent job of using technology to help students explore something that could otherwise not been seen with the naked eye.


10 minutes

The Build an Atom investigation is the last portion of the students' learning the parts of the atom.  After completing the investigation students will complete the Atomic Structure Exit Slip that summarizes PS1.A (see introduction), letting me know whether or not more teaching needs to occur. 

If more teaching needs to occur, students can either revise their concept maps, or if a good portion of the class is struggling, the following class begin by going over the Build an Atom investigation.  If time permits I have students grade them in class for instant feedback.

Modeling and questioning are my main focus for this unit.  This activity really hit home with getting students to do both.  One minor modification that helped some of the struggling students was to provide them with a starting point of Li for the back page of the assignment.  I found that it was easier for students to determine what was happening when a proton was added, or a neutron was removed.  This was a super easy, on the spot way to differentiate the assignment on an individual basis.