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Electrons and Ions Explained with Balloons (4 Favorites)

DEMONSTRATION in Atoms, Isotopes, Subatomic Particles, Electrons, Ions. Last updated July 30, 2021.


Summary

In this demonstration, helium balloons and clothespin weights are used to demonstrate how adding an electron makes a negative ion, and removing an electron makes a positive ion, a concept that is often confusing to students.

Grade Level

Middle School, High School

NGSS Alignment

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

  • MS-PS1-1: Develop models to describe atomic composition of simple molecules and extended structures.
  • HS-PS1-7: Use mathematical representation to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
  • Scientific and Engineering Practices:
    • Developing and Using Models

Objectives

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

  • Predict the charge of an ion.
  • Connect charges with subatomic particles.
  • Differentiate between anions and cations and how they are formed.

Chemistry Topics

This demonstration supports students’ understanding of:

  • Subatomic particles
  • Ions and Atoms

Time

Teacher Preparation: 15 min to make the helium balloon(s) neutrally buoyant with clothespin weights
Lesson: 30 minutes

Materials

  • 1 or 2 (or more) Mylar® balloons with ribbons of equal length attached
  • 6-12 mini clothespins, or as many as needed, to attach to the ribbons as weight to adjust the floating/sinking of the balloon
  • Tape, to add on to clothespins to act as small amounts of mass to adjust buoyancy
  • Permanent Marker, to write an “e” symbol on each mini clothespin

Safety

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

Teacher Notes

  • Students should be familiar with the three subatomic particles before this lesson. Therefore, the background reading should be review, and could be assigned with the pre-activity questions as homework before doing the demo in class. Additionally, knowledge of isotopes and writing isotope symbols is expected in the extension exercise but can be skipped if this is used as a middle-school activity or as an introduction to ions and charge.
  • Students often assume that adding something automatically means “positive,” and taking something away equates to “negative.” Of course, the opposite is true when adding negatives, like electrons in atoms. The goal of this demonstration with balloons and weights is to show that adding to something can make it more negative and can help students overcome this common misconception, which is a frequent cause of confusion when introducing the concept of ions and how they form.
  • Since latex allergies are becoming more common, Mylar® is recommended. Select Mylar balloons of the same size and shape. A latex balloon will work, but it will deflate within a day or two.
  • You only need one balloon for this demonstration, but you could get more than one balloon, filled with different amounts of helium to represent different atoms with different numbers of protons in their nuclei, thus requiring different numbers of electrons for a neutral atom.
  • In this demonstration, weights are used as a negative force pulling down and helium is used as a positive force pulling upward. The addition of weights represents the addition of a negative charge (electron). The use of a helium balloon is like the positive charge on a nucleus.
  • Practice explaining the concept before class. Each clothespin represents one electron for the atom, therefore a three-pin balloon represents an atom with 3 electrons, or lithium.
  • Demonstration Procedure:
    • Before starting the class, attach enough mini clothespins to the balloon ribbon(s) to weigh the balloon(s) down enough that it does not rise or sink. If you find that you cannot add an exact number of clothespins to get the balloon to be neutrally buoyant (doesn’t rise or sink), add pieces of tape to the clothespins to make minor mass adjustments.
      • This does not need to be perfect, but it should be close to neutrally buoyant so the balloons are not on the floor or on the ceiling all period. You may notice that air currents in the room affect the balloons.
      • Be sure that the ribbons and any attached clothespins are not resting on a desk/table or the ground.
    • Draw a vertical number line on the white board or chalk board with zero at the middle of the vertical line. (There is no need to write positive and negative numbers on the vertical number line, only indicate that positive is above zero and negative is below zero.)
    • Place the pre-weighted balloon(s) so that it hovers around zero on the number line.
    • Explain to students that the helium that causes the balloon to float represents the positive charge of the protons in the nucleus, and the clothespins that weigh the balloon down represent the negative charge of the electrons in the electron cloud.
    • Ask students if they can identify the atom the balloon represents. They should realize that the number of electrons (clothespins) in a neutral atom (the balloon when it is neutrally buoyant, at zero) equals the number of protons, which can be used to identify the atom.
    • Ask students what will happen if a clothespin is added or removed, and what will happen when the original number of clothespins is restored.
    • Demonstrate that as an electron (clothespin) is removed from the balloon, the balloon rises into the positive region on the vertical number line drawn on the board. This indicates a positively charged ion (cation).
    • Return the clothespin to the balloon. It should return to its neutral buoyancy. Line it up with the zero point on the number line again if it has shifted.
    • Demonstrate that as an electron (clothespin) is added to the balloon, the balloon sinks into the negative region on the vertical number line drawn on the board. This indicates a negatively charged ion (anion).
    • You can repeat the procedure with additional balloons with varying amounts of helium that would require different numbers of clothespins (representing different atoms).
  • Although this exercise focuses on electrons and charge, the calculations section reviews isotope symbols, numbers of subatomic particles, and mass number in addition to the concept of charge.

For the Student

Lesson

Background

There are three subatomic particles that combine to make atoms: protons, neutrons, and electrons. A proton has a +1 charge and an electron has a –1 charge. The neutron is neutral, and has zero charge.

Atoms have the same number of protons and electrons, making them neutral.  An ion is an atom that has an unequal number of protons and electrons and therefore the ion has a charge. Ions can have either a positive charge or a negative charge. A positively charged ion is called a cation and a negatively charged ion is called an anion.

Electrons are on the outside of the atom, so electrons can be lost or gained to create ions.  Protons and neutrons are in the nucleus of the atom and do not change in chemical reactions.

In this demonstration, the upward push of the helium in the balloon represents the positive charge of the protons in the nucleus, and the clothespins weighing the balloon down represents the negative charge of the electrons. A balloon that does not rise OR fall indicates a neutral atom, where the number of protons equals the number of electrons.

Pre-activity Questions

  1. What is the charge on an atom?
  2. Which subatomic particle has a positive charge?
  3. Which subatomic particle has a negative charge?
  4. Which subatomic particle is neutral?
  5. Which subatomic particle(s) is OUTSIDE of the nucleus?
  6. Which subatomic particle(s) is INSIDE the nucleus?
  7. Which subatomic particle can be added or removed in a chemical reaction?
  8. What charge does a cation have?
  9. What charge does an anion have?

Procedure

Observe your teacher as they add and remove clothespins from the balloon ribbon, and answer the following questions:

  1. What is the initial charge of the balloon “atom” according to the number line on the board?
  2. How many electrons are on the balloon “atom”? Use this to determine the identity of the atom it represents and explain how you came to your conclusion.
  3. What happens to the balloon when your teacher removes a clothespin “electron” from the balloon? What happens to the charge?
  4. Does this represent a cation or an anion?
  5. What happens when your teacher puts the clothespin back on the balloon? What happens to the charge?
  6. What happens when your teacher adds an additional clothespin to the balloon? What happens to the charge?
  7. Does this represent a cation or an anion?

Conclusion

Write a paragraph summarizing what you learned from this demonstration about the relationship between atoms, electrons, and the formation of ions. Be sure to address how both cations and anions are formed, and how they relate to the balloon model.

Extension

Previously, you learned about isotopes. Combine that knowledge with your new understanding of ions to complete the missing information in the table below. For the symbol, write the chemical symbol complete with atomic number, mass number, and charge (if applicable) written in the correct places (use number 1 as a guide).

Symbol
Mass number
Protons
Neutrons
Electrons
Charge
1
32
16
16
18
2–
2
17
18
1–
3
77
54
0
4
226
88
0
5
27
13
10
6
23
12
1+
7
83
126
80
8
55
30
23
9