Summary

In this activity, students will demonstrate their knowledge of ionic bond strength and its relationship to the properties of melting point and solubility using a “brackets” activity. After analyzing the ionic charge and radius to predict the strongest and weakest bond between four pairs of ionic substances, they will then determine which will be the least soluble.

Grade Level

AP and High School

AP Chemistry Curriculum Framework

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

• Unit 2: Compound Structure and Properties
  • Topic 2.1: Types of Chemical Bonds
    • 2.1.A: Explain the relationship between the type of bonding and the properties of the elements participating in the bond
  • Topic 2.3: Structure of Ionic Solids
    • 2.3.A: Represent an ionic solid with a particulate model that is consistent with Coulomb’s Law and the properties of the constituent ions.
• Unit 3: Properties of Substances and Mixtures
  • Topic 3.2: Properties of Solids
    • 3.2.A: Explain the relationship among the macroscopic properties of a substance, the particulate-level structure of the substance, and the interactions between these particles.

NGSS Alignment

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

• 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.
• HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data
  • Engaging in Argument from Evidence

Objectives

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

• Estimate the relative strength of an ionic bond in two substances.
• Identify which of two substances will have lower solubility based on the strength of the ionic bonds.

Chemistry Topics

This activity supports students’ understanding of

• Ionic Bonding
• Chemical Formulas
• Physical Properties: Melting Point and Solubility

Time

Teacher Preparation: minimal

Lesson: 45 - 60 minutes

Materials

• Student Handout

Teacher Notes

• Ionic properties such as melting point and solubility are related to the strength of the ionic bond. As a general rule:
  • Ionic compounds with stronger ionic bonds will have higher melting points and lower solubility.
  • Ionic compounds with weaker ionic bonds will have lower melting points and higher solubility.
  • Ionic bonds resulting from ions with higher charges will generally have higher melting points and lower solubility than those with lower charges.
  • Ionic bonds between ions with smaller radii with generally have higher melting points and lower solubility than those with larger radii.
• It is important to stress that these rules are general rules, not absolute trends.
• This activity should be used as a summative assessment following a comprehensive study of ionic compounds, bonding, and properties.
• The compounds students will compare will have similar ionic radii and different charges or similar charges and different ionic radii. There is no case where both will be different.
• There are two sets of brackets. Provide each pair/group of students with one of the brackets. When they finish their bracket they should find a group with the other bracket and come up with the ultimate winner.
• The central question in this activity is, “Predict which compound will be least soluble?” This question can easily be changed:
  • Predict which compound will be most soluble.
  • Predict which compound will have the lowest melting point.
  • Predict which compound will have the highest melting point.