Our site will be under maintenance on Saturday, Nov. 16, 2024 from 6pm EST until midnight. Thanks for your patience!

« 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?

Periodic Trends II: Electron Affinity, Atomic Radius, & Ionic Radius Mark as Favorite (77 Favorites)

ACTIVITY in Periodic Table, Atoms, Model of the Atom, Valence Electrons, Subatomic Particles, Atomic Radius, Ionic Radius, Electron Affinity, Electrons, Ions, AACT Simulations. Last updated October 03, 2024.

Summary

In this simulation, students will focus their investigation on the electron affinity of an atom. Through the use of this simulation students will have the opportunity to examine the formation of an anion as well as compare the atomic radius of a neutral atom to the ionic radius of its anion.

Grade Level

High school

AP Chemistry Curriculum Framework

This simulation supports the following unit, topics and learning objectives:

  • Unit 1: Atomic Structure and Properties
    • Topic 1.5: Atomic Structure and Electron Configurations
      • 1.5.A: Represent the electron configuration of an element or ions of an element using the Aufbau principle.
    • Topic 1.7: Periodic Trends
      • 1.7.A: Explain the relationship between trends in atomic properties of elements and electronic structure and periodicity.
    • Topic 1.8: Valence Electrons and Ionic Compounds
      • 1.8.A: Explain the relationship between trends in the reactivity of elements and periodicity.

Objectives

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

  • Predict that the ionic radius of an anion will be larger than the atomic radius of its neutral atom.
  • Identify the general trend of increasing electron affinity value from left to right within a period.
  • Recognize the trend of increasing ionic radius in a group such as the halogens.
  • Explain that the addition of an electron to an atom, and the formation of an anion is an exothermic process.
  • Recognize the impact of sub-atomic particles and atomic organization on the electron affinity value of an atom.
  • Understand the relationship between electron affinity, atomic radius and ionic radius.

Chemistry Topics

This lesson supports students’ understanding of

  • Atomic Structure
  • Periodic Trends
  • Electron Affinity
  • Atomic Radius
  • Ionic Radius
  • Model of the Atom

Time

Teacher Preparation: minimal

Lesson: 45 minutes

Materials

Safety

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

Teacher Notes

  • The student handout/instructions assume that a student knows the difference between a “group” and a “period.”
  • The student should understand the periodic trends of atomic radius and ionization energy, as well as a basic understanding of nuclear charge and shielding effect in order to successfully use the student handout.
  • There is a separate simulation, Periodic Trends I: Ionization Energy, Atomic Radius & Ionic Radius that can be used for teaching students about the relationship between these specific trends as well as cation formation.
  • Please note that Nitrogen is not a selectable atom in this simulation. Nitrogen is an anomaly and does not follow the general trend for affinity, as it has an extremely low/not stable value for its first electron affinity, due to its orbital stability (p3).
  • Electron affinity is defined as the amount of energy released when an atom gains an electron in order to for a negative anion. This is an exothermic process, and therefore the data values included in the simulation are denoted with a negative (-) sign.

For the Student

Background

In this investigation you will examine the electron affinity of select atoms from the periodic table. You will have the opportunity to analyze the effect that electron affinity has on other periodic trends, including atomic radius and ionic radius.

  1. What subatomic particles are located in the nucleus of an atom? Does the nucleus of the atom have a charge? Is so, what is it?
  2. What factors determine the size (radius) of an atom? Explain.
  3. Draw a Bohr model for Magnesium (Mg) and Chlorine (Cl). Which atom should be larger?
  4. Is it more difficult to remove a valence electron from a Magnesium (Mg) atom or a Chlorine (Cl) atom? Explain.
  5. What does a positively charged ion indicate in terms of its subatomic particles? Use the Calcium ion Ca+2 as a specific example in your explanation.
  6. What does a negatively charged ion indicate in terms of its subatomic particles? Use the Fluoride ion F-1 as a specific example in your explanation.

*Check your answers before moving on to the next portion of the activity.

Procedure

Using your computer, tablet or mobile device, navigate to the website: teachchemistry.org/electron-affinity

You should see the picture below on your screen:

Investigation

  1. Choose any element shown in green from group 7 on the periodic table by clicking the on the element symbol. You should see details about the element that you chose appear at the bottom of the screen. An example is shown below:
  • a. How many valence electrons are present in this atom?
  • b. How can this atom become stable?
  • c. Attempt to add an electron to the atom. Describe what happened:
  • d. Comparing the neutral atom and its anion, what do you notice about the radius in the side-by-side comparison? Do the data values support the visual representation?
  • e. Are there any other noticeable differences between the neutral atom and its anion (other than size)? List them below:
  • f. Explain why there is a difference in size between the neutral atom and its anion, making specific reference to subatomic particles.

Reset the selected data using the reset symbol.

  1. Choose any element shown in green from group 1 on the periodic table by clicking the on the element symbol. You should see details about the element that you chose appear at the bottom of the screen. An example is shown below:
  • a. How many valence electrons are present in this atom?
  • b. How can this atom become stable?
  • c. Attempt to add an electron to the atom. Describe what happened:
  • d. Why did this atom behave differently than the atom chosen in question 1?

Reset the selected data using the reset symbol.

  1. Choose one of the following elements by clicking on the element symbol:
    1. Oxygen (O)
    2. Phosphorous (P)
    3. Sulfur (S)

You should see details about the element that you chose appear at the bottom of the screen.

  • a. How many valence electrons are present in this atom?
  • b. How can this atom become stable?
  • c. Attempt to stabilize the atom by adding the necessary number of electrons. Describe what happened:
  • d. Comparing the neutral atom and its anion, what do you notice about the radius in the side-by-side comparison? Do the data values support the visual representation?
  • e. Are there any other noticeable differences between the neutral atom and its anion (other than size)? List them below:
  • f. Explain why there is a difference in size between the neutral atom and its anion, making specific reference to subatomic particles.
  1. Consider the elements located in group 7 on the periodic table.
  • a. What do you notice about the electron affinity values for each of these group 7 elements compared to the values for other elements that are in the same period?
  • b. Which atom in group 7 should have the largest atomic radius (consider only F, Cl, Br and I)? Why?
  • c. Based on your answer to part b, and what you have learned so far, which anion in group 7 should have the largest ionic radius (consider only F-1, Cl-1, Br-1 and I-1)? Why?
  • d.Interact with the simulation and select the atoms mentioned in part b & c., to determine if your predictions are correct. Explain your analysis below:
  • e. Based on your answers above, can you make a general statement about the ionic radius trend of anions within a group?

Review Questions

  1. Decide whether the following statements are true or false, and briefly explain your choice in the space provided after each statement:
  • a. True or False: Metals usually have stronger electron affinity than non-metals.
  • b. True or False: Noble gas elements have a very large value for electron affinity.
  • c. True or False: Negative anions have a larger ionic radius than the atomic radius of their neutral atom.
  • d. True or False: The value for electron affinity is a negative value because when an electron is added to the outer shell of an atom, energy is released.
  • e. True or False: Electron affinity values generally increase from left to right in a period on the periodic table.
  • f. True or False: A larger numerical value for electron affinity means it is more difficult for an electron to be added to an atom.

Using the simulation, check your predicted answers to see if you are correct!