Summary

In this lesson, students will answer questions about rocks and minerals while listening to a podcast from Tiny Matters. They will then learn how to balance charges to create neutral sets of ions, representing minerals, by using the provided ion cards.

Grade Level

High school

NGSS Alignment

This lesson will help prepare your students to meet performance expectations using the following practices:

• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking
  • Developing and Using Models

Objectives

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

• Identify minerals as pure chemical substances.
• Use ion charges to determine complete ionic chemical formulas for minerals.

Chemistry Topics

This lesson supports students’ understanding of:

• Ionic bonding
• Polyatomic ions
• Empirical formula

Time

Teacher Preparation: ~45 minutes

Lesson:

• Part 1: 10-15 minutes, plus 34-minute podcast
• Part 2: 30-50 minutes

Materials

• 1 set of 96 ion cards per pair/group of students
  • There are 3 copies of the 32 cards – repetitions are intentional
• Podcast Episode: Zircon: How this tiny, ancient mineral is upending what scientists believed about early Earth

Safety

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

Teacher Notes

• This lesson is intended to be an introduction to balancing charges to write ionic compound formulas. The author has found this to be an intuitive way for students to develop mathematical reasoning by modeling minerals with sets of ion cards and adding the charges in attempt to reach a net sum of zero.
• Pre-requisite knowledge for this activity:
  • Notation of chemical formulas, ions, charges
  • Working definitions of element, compound, ionic compound, ion, molecule
• You can access the podcast from the link or any podcast platform listed there:
  • Zircon: How this tiny, ancient mineral is upending what scientists believed about early Earth
  • It is recommended that students be allowed to listen independently to the podcast while answering questions so they can pause, slow down, or repeat segments as needed.
• Copy and cut ion cards with a paper cutter (optional – laminate them for future use).

Part 1:

• Page 1 of the student handout can be done collaboratively or as a teacher-led activity, as students may have last seen the rock cycle in either middle school or in a high school earth science class. The warm-up questions provide prompts for students to think about what they may remember about the rock cycle.
• After the warm-up, briefly review the following points to give context to the information in the podcast. Students should take notes in their “Notes about the Rock Cycle” section.
  • Deep inside the earth a giant mixture of elements and compounds in liquid form is always moving.
  • Minerals are pure substances with a definite chemical composition that form when portions of the liquid mixture cool.
  • Small fragments of many minerals that solidify from the liquid mixture can form a solid mixture that we call a rock.
• Copy or project the diagram from page one of the student activity onto the front board. Refer to this diagram and discuss each of the points shown in this section of the answer key document.
  • When portions of this mixture cool, either inside the earth (from magma) or on the earth’s crust (from lava), igneous rocks are formed. The mixture may contain elements or compounds that have been there since the earth formed and it may contain elements or compounds that have gone through portions of the rock cycle.
  • Igneous rocks may cycle back into the liquid portion of earth or may stay on the earth’s surface and get weathered and eroded.
  • Sedimentary rocks form when lots of fragments of other rocks get compressed into new mixtures and typically form layers. These rocks may cycle back into the liquid portion of earth or may stay on the earth’s surface and get weathered and eroded again.
  • Metamorphic rocks form when other rocks are subjected to heat and pressure, changing the nature and composition of the original rocks. These rocks may cycle back into the liquid portion of earth or may stay on the earth’s surface and get weathered and eroded.
  • When rocks cycle back into the liquid phase, no trace of the original rock will remain because the rock was just a mixture of minerals. Minerals, however, may survive certain cycles if the varying conditions don’t cause their bonds to break.
• Students may complete the active listening section during class or as homework. The podcast is ~34 minutes long. There is a “Tiny Show and Tell” at the end that is unrelated to the major topic. The teacher should decide and instruct the students whether they should listen to this or not. It is only the last ~2-3 minutes of the podcast.

Part 2:

• Review or discuss answers to the podcast questions.
• Reinforce that minerals are pure substances, mostly compounds, that form naturally so they are mixed up with a bunch of other pure substances. This is why it is rare to find large samples of pure minerals that have crystallized without being interrupted by other compounds.
• Direct students to read the Background Information, then ask probing questions to ensure students understand what is meant by monatomic and polyatomic ions.
• Direct students to read and answer questions 1 and 2, then review answers and discuss as needed.
• Groups of 2-3 students will each use a set of ion cards that the teacher prepared. A good way to explain the activity is to use a card set for demonstration before distributing them to students. Before class begins, find all copies in the demo set of the cards containing Cu²⁺, CO₃^2-, and OH^-. Use magnets to hang these on the whiteboard, grouped by ion (all the Cu²⁺ cards together, etc.).
  • Refer students to the first mineral on the worksheet, azurite. Ask them what kinds of ions azurite contain. [Answer: copper(II), carbonate, hydroxide]
  • Point to the cards you have magnetically attached to the whiteboard and explain that compounds form from samples containing billions of atoms/ions, but that you are just looking to find the smallest ratio in which they can combine so you won’t use all available cards.
  • Bring one card for each ion away from their groups and into a new grouping together.
  • Ask students if this grouping of ions has an overall neutral charge and could represent a compound. Clarify any confusion or misunderstanding about how to sum up the charges. [Answer: No, it has a net charge of -1]
  • State that, since azurite contains all three ions, the final formula must contain at least one of each of the three ions.
  • Ask whether the set needs more ions that are positive or more that are negative to reach a neutral charge. [Answer: needs more positive]
  • The only ion in the set with a positive charge is copper(II) ion, so bring another Cu²⁺ card into the combined set and ask students if it is neutral.
  • Repeat in this way until a neutral compound is reached
  • Demonstrate how to fill out the chart for azurite:

• Some minerals will have different ways of reaching neutrality (like choosing between two different ions that have the same charge). The goal is to reach any set that is neutral.
• Many students will naturally look for ways of making it “easier”, which strengthens their mathematical reasoning, and makes determining formulas for ionic compounds made of only two types of ions – which are more typical in high school chemistry classes – seem comparably simple.
• For many students, this can be an activity worth taking the classroom time to complete. For students who “catch on” more quickly, you can reduce the length by omitting some of the minerals.
• This activity can be quickly reviewed during the next class period with a focus on writing chemical formulas for simpler ionic compounds and adding the skill of naming the compounds from the formulas.
• An Answer Key is available for teacher reference.
• Related resources from the AACT library:
  • Chemistry Solutions Article: Part 1 Teaching Earth Chemistry
  • This is the first article in a 4-part series, with associated lessons, that model ways of integrating chemistry and earth science, as suggested in the NGSS Modified Science Domains Model, sometimes called the 3-Course Model.