Summary

In this lesson, students will model the location and behavior of protons, neutrons, and electrons that make up the structure of atoms, focusing on the first 18 elements on the periodic table. Students will model different elements first by adding protons and neutrons (colored balls) to make the nucleus (a basket). Then, the students themselves will represent the electrons that are always moving around the nucleus yet remaining within their designated energy level. This activity is easiest to complete outside or in a large open room to allow for enough room.

Grade Level

Middle School, High School

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

• MS-PS1-1: Develop models to describe the atomic composition of simple molecules and extended structures.
• Scientific and Engineering Practices:
  • Developing and Using Models

Objectives

By the end of this lesson, students should be able to:

• Identify the different parts of an atom.
• Determine the atomic number, atomic mass, and the number of protons, neutrons and electrons for each atom.
• Realize that electrons are not stationary, but always moving within their energy levels.

Chemistry Topics

This lesson supports students’ understanding of:

• Model of the atom
• Atomic structure
• Subatomic particles
• Elements
• Periodic Table

Time

Teacher Preparation: 20 minutes
Lesson:40-50 minutes

Materials

• 40 balls of two colors
  • 18 one color = protons (labeled with a + sign), 22 another color = neutrons
  • Any type of small ball could be used – tennis balls, rubber balls, refill balls for a ball pit, ping-pong balls, etc.
• 2 containers (one to hold protons and the other to hold neutrons)
• 1 basket (to hold the balls representing protons and neutrons in the nucleus)
• Sidewalk chalk or rope/string – something to make circles to represent the energy levels
• Periodic Table Chart of the first 18 elements (available for download in the sidebar; I make this into poster size), or full periodic table
• Student handout (optional)

Safety

• No specific safety precautions need to be observed for this activity.

Teacher Notes

• Students should have been introduced to the periodic table, atoms, and subatomic particles prior to this lesson. They should be familiar with how to determine the number of each subatomic particle in an atom, as well as their location, mass, and charge.
• This lesson was designed for a middle school audience but could also be used in an introductory high school chemistry course.
• This lesson is easiest to complete outside or in a large open room to allow for enough room for students to move around as they model electrons in the first three energy levels. Outside, chalk could be used to draw circles representing energy levels. Indoors, string or rope could be used instead. See the Model Setup download in the sidebar for a diagram.
• Begin the lesson by having students think about the “Pre-activity Questions” from the student handout. This could be done verbally as a class discussion, or you could distribute copies of the student activity sheet for students to respond in writing. You could pose these questions to the whole class, or have students discuss them in pairs/small groups first and then share their responses as a whole class. Sample answers you might expect are in the answer key (available in the sidebar).
  • If you do not have students complete the written section of the activity sheet, you may want to distribute copies of the instructions or display them at the front of the classroom, in addition to going over them out loud.
• In the pre-activity questions, students are asked about isotopes – they may not know anything about isotopes yet, so it is a good time to introduce the idea that atoms of the same element can have different numbers of neutrons and therefore different masses, so the decimal number on the periodic table is the average mass of all the atoms of that element. Explain that in middle school they won’t need to worry about isotopes and can round the atomic mass to a whole number. Provide an example, such as lithium: its atomic mass on the periodic table is 6.94, thus we will round and say that lithium’s mass number (for the purposes of this exercise) is 7. This is a good way to keep it simple for a middle school-level introduction while also letting students know that the reality is a bit more complicated and will be addressed in future chemistry classes.
• If you think your students need a review, remind them that the number of protons is the same as the atomic number, the number of electrons in atoms is the same as the number of protons, and the number of neutrons can be found by subtracting the number of protons from the mass number. To use the lithium example again, the mass number is 7 and there are 3 protons, so there must be 7 – 3 = 4 neutrons.
• If you do not use the student activity sheet for written responses, you could instead discuss the Analysis questions after completing the activity. It could be a whole-class discussion, or you could start out with students in pairs/small groups before sharing out.
• At the end of the activity, you could also ask students to pose any remaining questions they have about subatomic particles or atomic structure. If they are questions they should already know the answer to, you can see if the class can come up with an answer. If they are questions you have not addressed yet in class, you can make a note of them for future lessons.
• There is a related follow-up activity, Understanding Static Electricity, that can be used to explore the relationship between atomic structure and static electricity.
• This lesson helps students understand the locations of subatomic particles within atoms, but not necessarily the relative size/scale of the particles and the space between the electrons and the nucleus. A good lesson from the AACT resource library to help students realize just how much of an atom is actually empty space is Investigating the Sizes of Atomic Particles.

Activity instructions:

*Note that I have used red balls for protons and yellow balls for neutrons in the steps listed below, but you can use whatever colors you want/have available.*

1.  Have students line up around the outside of the atom (circles) and place the periodic table chart on a chart stand so all the students can see.
2. Create the first element, hydrogen: have the students say how many protons to place into the nucleus (1) and then ask “What is hydrogen’s mass number?” (1) Then ask “How many neutrons would that be?” (1-1=0) Have the first student in line take one red ball to represent protons and no yellow balls for neutrons and place it in the nucleus (basket). Now l ask the students, “How many electrons should hydrogen have?” (1) Have the student that placed the ball in the nucleus become the electron and walk around the first energy level.
3. Create helium: have the students say how many protons to place in the nucleus (2) and then ask “What is helium’s mass number?” (4) “How many neutrons?” (4-2=2) Have the second student in line take one more red ball to represent another proton (there is already a proton in the basket from hydrogen) and 2 yellow balls for neutrons and place them in the nucleus. Next, ask the students, “How many electrons should helium have?” (2) Once more, the student that placed the balls in the nucleus will become the second electron and walk around the first energy level.
4. Create lithium: have the students say how many protons to place in the nucleus (3) and then ask “What is lithium’s mass number?” (7) “How many neutrons?” (7-3=4) Have the third student in line take one more red ball to represent another proton and 2 more yellow balls for neutrons (there are already 2 in the basket from helium) and place them in the nucleus. Next, I will ask the students, “How many electrons should helium have?” (3) Once more, the student that placed the balls in the nucleus will become the electron and walk around the second energy level (since the first energy level can only hold two electrons).
5. Create beryllium: at this point, you could have a student ask the questions once they have the hang of it, and they would ask the next student in line how many protons should be in the nucleus (4) and then ask “What is beryllium’s mass number?” (9) “How many neutrons?” (9-4=5) They will have the fourth student in line take one more red ball to represent another proton and 1 more yellow ball for a neutron (there are already 4 from lithium) and place them in the nucleus. Next, they will ask the students, “How many electrons should beryllium have?” (4) Once more, the student that placed the balls in the nucleus will become the electron and walk around the second energy level. Now the teacher’s role is to supervise and correct when needed.
6. Create boron: the student will ask the class how many protons should be in the nucleus (5) and then ask “What is boron’s mass number?” (11) “How many neutrons?” (11-5=6) They will have the fifth student in line take one more red ball to represent another proton and 1 more yellow ball for a neutron (there are already 5 neutrons from beryllium) Next, they will ask the students, “How many electrons should boron have?” (5) Once more, the student that placed the balls in the nucleus will become the electron and walk around the second energy level.
7. Continue like this until the class reaches Argon.
8. If you want all your students to get a chance to participate, you can now choose one of the 18 elements (starting at larger elements and working toward the smaller ones) for the student to act out and this time, they will remove protons and neutrons from the basket and then they will have some electrons leave the atom.

There is a Reference Table “cheat sheet” in the sidebar that lists the number of protons, neutrons, and electrons for each element in this activity.