« Return to AACT homepage

AACT Member-Only Content

You have to be an AACT member to access this content, but good news: anyone can join!


Need Help?

Coulomb's Law (13 Favorites)

LESSON PLAN in Electrostatic Forces, Subatomic Particles, Ionization Energy, Electrons. Last updated September 7, 2018.


Summary

In this lesson students explore qualitative applications of Coulomb’s law within atoms and between ions and solvents.

Grade Level

High School (AP Chemistry)

AP Chemistry Curriculum Framework

Choose the Big Idea associated with this Lesson Plan:

  • Big Idea 1: The chemical elements are fundamental building materials of matter, and all matter can be understood in terms of arrangements of atoms. These atoms retain their identity in chemical reactions.
    • 1.8 The student is able to explain the distribution of electrons using Coulomb’s law to analyze measured energies.
  • Big Idea 2: Chemical and physical properties of materials can be explained by the structure and the arrangement of atoms, ions, or molecules and the forces between them.
    • 2.14 The student is able to apply Coulomb’s law qualitatively (including using representations) to describe the interactions of ions, and the attractions between ions and solvents to explain the factors that contribute to the solubility of ionic compounds.

Objectives

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

  • Apply Coulomb’s law qualitatively to ionization energy and lattice energy
  • Use correct vocabulary to explain trends in ionization energy and lattice energy

Chemistry Topics

This lesson supports students’ understanding of

  • Coulomb’s law
  • Ionization energy
  • Lattice energy

Time

Teacher Preparation: 10 minutes

  • Lesson: 180 minutes
    • 30 minutes for Move that Magnet
    • 30 minutes for Coulomb’s Law Computer Simulation
    • 60 minutes for Successive Ionization Guided Inquiry
    • 60 minutes for the Lattice Energy Guided Inquiry

Materials

Safety

  • Do not allow the Neodymium Disc Magnets to snap to each other or to any magnetic surface as the magnets may pinch fingers, break, or shatter.
  • Keep strong magnets away from pacemakers.
  • Magnets may pose a choking hazard.

Teacher Notes

  • Coulomb’s Law Background Information for the Teacher:
  • Move that Magnet!
  • The goal of this introductory activity is to see and feel the general patterns in Coulomb’s Law. This activity is not written to have students derive the Coulomb’s law equation.
    • Many students have prior experiences working with charged particles (static electricity) and magnets. This simple inquiry lab harnesses students’ prior knowledge through magnets.
    • If a student has not taken a physics class yet, the concept of a “force” might be new to them. With the magnets, students will be able to feel and see attractive and repulsive forces. This will help them understand the force arrows drawn in future lessons.
    • Students will be able to see how distance affects attractive/repulsive forces by holding the magnet closer and farther away from the other magnet.Students will also see how the magnitude of charge affects attractive/repulsive forces by using different strength magnets.
  • This activity is written for lab groups of 2-4. Lab partners would be ideal if there are enough supplies available.
  • Students are not required to develop a procedure or data table for this inquiry lab. This keeps the activity quick as its goal is to elicit prior knowledge. However, you can expand this activity to include a formal procedure and data table if you have time.
  • This activity can be modified if supplies are missing:
    • If you don’t have magnets, you can substitute with two blown-up balloons instead. Students can charge the balloon (not attached to the string) with static electricity by rubbing it with a cloth or head. To change the amount of charge on the balloon, the balloon can be rubbed more or less. If students rub the balloon on their head for a long time (10 sec), they may accidently dispel the charge before they can hold it up to the other balloon.
    • If you do not have a ring stand to suspend a magnet by a string, you can stand a round magnet on it side and it should roll towards the other magnet when it is attracted to it. The goal of suspending the magnet from a string is to minimize friction.
    • Students can also explore with the following PhET Simulations if no supplies are available:
    • Balloons and Static Electricity (HTML5)
    • Electric Field Hockey (JAVA) Students use Coulomb’s law to make a goal with a charged hockey puck. This simulation has not been updated to HTML5 (as of June 2018). Check to make sure it will work on your devices at your school before the lesson.
  • Have a whole class discussion where students share out their conclusions and analysis answers. The teacher should be able to tease out the Coulomb’s law concepts: like charges repel, opposite charges attract, force of attraction or repulsion increases by increasing the size of the charge (strength of magnet) and decreasing the distance between charged objects. It might be a good idea for students to add to their Conclusion summary after the whole class discussion.
  • All diagrams were drawn by the author, Melissa Hemling
  • Coulomb’s Law Computer Simulation
  • The goal of this activity is to build off of the previous magnet lab and develop the Coulomb’s Law equation.
  • The supplies used in the previous activity were too crude to develop Coulomb’s law (but allowed students to feel the forces of attraction and repulsion). This computer simulation it detailed enough to help students develop Coulomb’s Law.
  • In this simulation, the red particle represents the proton (positively charged and stationary) while the blue particle represents the electron (negatively charged and mobile). While this is not perfect representation of the atom, it is good enough to get the basic equation of Coulomb’s Law and see how Coulomb’s Law can be applied to atoms.
  • Students should work in pairs, each with their own computer. This way they can discuss and bounce ideas off of each other during the activity.
    • Coulomb’s Law computer simulation
    • It is a HTML5 simulation so it should work on any device that can access an internet browser like Chrome and the internet.
    • If you use an LMS like Moodle or Google Classroom, it may be helpful to post the simulation link online for students to quickly access. It is also hyperlinked in the student version of the activity.
  • Before students begin using the simulation, it would be beneficial to demonstrate how to use the simulation, all of the controls, and which particle is the proton and electron through a computer projector like a SMART board.
  • The teacher may need to guide students in questions 5-7, depending on the mathematical and chemical backgrounds of the students.
  • Have a whole class discussion where students share out their conclusions and analysis answers. The teacher may choose to use the simulation to confirm student conclusions in front of the class on a SMART board. The teacher should try to make connections between the magnet activity and this simulation. It might be a good idea for students to add to their Conclusion summary after the whole class discussion.
  • All diagrams were drawn by the author, Melissa Hemling
  • Successive Ionization Energy Guided Inquiry
  • The goal of this activity is to connect Coulomb’s law to ionization energy. It is important for AP Chemistry students to be able to use Coulomb’s Law to justify trends in ionization energy on the AP Chemistry exam.
  • If your students do not understand Bohr diagrams, shells, valence electrons, and core electrons, please review before using this activity. It is assumed to be prior knowledge.
  • Bohr models are used in the “Models” of this guided inquiry activity. While some Bohr models show electrons paired in the shells and others show electrons as far apart as possible in each shell, it was decided to add electrons to shells clockwise to make the valence electrons easier to analyze. When electrons were placed as far apart as possible, some students missed the differences in number of valence electrons (which is key for this activity).
  • Students will be drawing arrows to represent the effective nuclear charge. Use the Teacher Background Information videos linked above to familiarize yourself with this concept to help students during the activity. Students will measure arrows to communicate the strength of the force. Due to the size of the atoms in the model, the arrows increase or decrease in size by 1 mm. The arrow will be really short for some of the electrons. The goal is to see the relative difference in effective nuclear charge. As students complete this part of the activity, circulate and make sure they are following the directions for calculating the size of the arrows, looking to make sure the relative differences in size of arrows are accurate.
  • Make sure students read the Background section before beginning. To introduce the connection between force of attraction and ionization energy have students “act out” by grabbing a pencil from one another in pairs.
    • One student will act as the positive nucleus and hold onto the pencil that represents the valence electron. The strength that the student acting as the nucleus has represents force of attraction. The other student represents ionization energy.
    • At first the “nucleus” student should hold onto the pencil lightly between two fingers with arms outstretched. The “ionization energy” student should try to take the pencil away and should notice that it required very little energy to remove the pencil from the hand. Weak force of attraction = low ionization energy.
    • Next the “nucleus” student should hold onto the pencil tightly with both hands and close to their body. The “ionization energy” student should try to take the pencil away and should notice that it required much more energy to remove the pencil from the hand. Strong force of attraction = high ionization energy.
  • This activity is written for students to work in collaborative groups of 2-4 with a teacher actively facilitating and checking understanding throughout.
  • Visit the POGIL.org website for more information about implementing a guided inquiry activity in your classroom and consult their implementation guide.
  • It is very important that the instructor frequently checks in with groups to check answers as the questions build off of one another.
    • You may just look over student’s shoulders or eavesdrop on conversations to quietly monitor progress and step-in when groups get confused.
    • You may have groups check in with you after key questions to check multiple questions at once.
    • You may decide to have a whole-class discussion after each Model to confirm accuracy and understanding.
    • If groups are confused, step in and help guide them to a correct understanding through a private conversation or whole class discussion.
  • The following areas of the activity may need assistance from a teacher:
    • The Read This! Section and question 5 may be sticking points for your students as it introduces new concepts. Question 5 requires students to draw arrows to represent effective nuclear charge. It may be nice to discuss effective nuclear charge and model how to do this in front of the class before hand or when groups reach this question.
    • Question 13 may be another sticking point where they draw in repulsive arrows. You may need to help model this to the class.
  • After the activity: Have a whole-class discussion to summarize and clarify concepts and vocabulary like effective nuclear charge and electron-electron repulsions . Encourage students to add to their Conclusion section after the discussion.
  • Have students complete a released free response question concerning ionization energy.
  • All diagrams were drawn by the author, Melissa Hemling
  • Lattice Energy Guided Inquiry
  • The goal of this activity is to have students justify qualitative trends in lattice energy using Coulomb’s law. This activity compares and contrasts how to use Coulomb’s law to justify ionization energy versus lattice energy trends. Students often use the wrong vocabulary (confuse ionization energy and lattice energy) when answering these questions on the AP Chemistry test.
  • Students should understand the basics of ionic bonds and crystal lattices before completing this activity. It is considered prerequisite knowledge. Students should have a general understanding of how ionic substances dissolve in water. Understanding how to use the periodic table to determine ionic size might be helpful as well.
  • The cations in this guided inquiry are the same ones used in the Successive Ionization Energy Guided Inquiry to provide continuity and help make connections.
  • This guided inquiry is structured to follow the Successive Ionization Energy Guide Inquiry. This sequence follows some AP textbooks as atoms and periodic trends are usually covered before bonding. If you choose to do these guided inquiries out of order, be sure to cover ionization energy beforehand or skip the ionization energy questions. If you cover lattice energy before ionization energy, I would suggest waiting to use this activity until you cover ionization energy. Then use both the Successive Ionization Energy and Lattice Energy Guided Inquiries back-to-back as a good review of lattice energy.
    • The crystal lattice structures in the Models are not drawn accurately. These simple models are meant to show the relative size of the ions and ratios of ions in the formula in order to analyze lattice energy only.
    • This activity is written for students to work in collaborative groups of 2-4 with a teacher actively facilitating and checking understanding throughout.
  • Visit the POGIL.orgwebsite for more information about implementing a guided inquiry activity in your classroom and consult their implementation guide.
  • It is very important that the instructor frequently checks in with groups to check answers as the questions build off of one another.
    • You may just look over student’s shoulders or eavesdrop on conversations to quietly monitor progress and step-in when groups get confused.
    • You may have groups check in with you after key questions to check multiple questions at once.
    • You may decide to have a whole-class discussion after each Model to confirm accuracy and understanding.
    • If groups are confused, step in and help guide them to a correct understanding through a private conversation or whole class discussion.
  • The following areas of the activity may need assistance from a teacher:
    • The summary chart in question 4 might confuse students. A whole class discussion or sharing of answers between groups might help those that struggle. This question is important to clarify the differences in using Coulomb’s law with ionization energy versus lattice energy.
    • Question 8c may be challenging. To help students out, you may want to draw a particulate diagram of dissolved ions in water.
    • Question 10 is where students apply their learning to a new set of compounds. Make sure to check and discuss ranking and justifications.
    • The summary chart in question 11 might confuse students. A whole class discussion or sharing of answers between groups might help those that struggle. This question is important to clarify the differences in using Coulomb’s law with ionization energy versus lattice energy.
  • After the activity: Have a whole-class discussion to summarize and clarify concepts and vocabulary. Encourage students to add to their Conclusion section after the discussion.
  • Have students complete a released free response question concerning lattice energy.
  • All diagrams were drawn by the author, Melissa Hemling