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How do atoms combine? Bonding and Shapes of Molecules

Learning Module

Chemistry is the study of matter, and to have a complex understanding of the world around us, it is imperative that students have an in-depth understanding of how atoms combine with each other to create the substances around them. This unit is designed for an introductory honors level high school chemistry class. It covers the types of bonds, naming and writing formulas for binary covalent compounds, Lewis Structures, VSEPR theory and the shapes of molecules, and intermolecular forces. Students in this class should have a basic understanding of atoms, and basic atomic structure including protons, neutrons, and electrons and valence electrons should be familiar to students.

As a result of completing this Learning Module, the students will be able to :

  • Distinguish between ionic, covalent, and metallic bonds.
  • Name and write formulas for binary covalent compounds.
  • Draw Lewis Structures for simple molecules.
  • Identify the 3-dimensional shape of a molecule using VSEPR theory.
  • Label the intermolecular forces present between molecules.
  • Explain how the shape of molecules affect its properties. 

Next Generation Science Standards Disciplinary Core Ideas Addressed:

PS2.B: Types of Interactions. Attraction and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter, as well as the contact forces between material objects. (secondary to HS-PS1-1),(secondary to HS-PS1-3)

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. [Clarification Statement: Examples of properties that could be predicted from patterns could include reactivity of metals, types of bonds formed, numbers of bonds formed, and reactions with oxygen.] [Assessment Boundary: Assessment is limited to main group elements. Assessment does not include quantitative understanding of ionization energy beyond relative trends.]

HS-PS1-3. Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles. [Clarification Statement: Emphasis is on understanding the strengths of forces between particles, not on naming specific intermolecular forces (such as dipole-dipole). Examples of particles could include ions, atoms, molecules, and networked materials (such as graphite). Examples of bulk properties of substances could include the melting point and boiling point, vapor pressure, and surface tension.] [Assessment Boundary: Assessment does not include Raoult’s law calculations of vapor pressure.]

Update 1

For the Student

By the end of this lesson, you should be able to describe the properties of covalent and ionic bonds. 

There are only 92 naturally occurring elements, but millions of different materials on this planet. Atoms combine to form different molecules and compounds and are held together by chemical bonds. Two main types of bonds are covalent and ionic bonds. Covalent bonds involve the sharing of valence electrons and occur between non-metals. Ionic bonds involve the attraction between opposite charged ions formed from the transfer of valence electrons. 

Media embedded November 25, 2018
Media embedded November 25, 2018

Comment: Create a "bumper sticker" slogan for either ionic or covalent bonds. 

Update: Read the article "Linus Pauling: American Hero". The article talks about three main contributions that Linus Pauling made to society: His model of chemical bonding, his work on proteins, and his work for world peace. What do you think was his most important contribution? Why? Use evidence from the article to defend your position.

Respond: Read at least 3 other students' updates and respond. Did you agree with their position? Where there any ideas presented in the update that caused you to reconsider what you had previously thought?

For the Teacher

By the end of this lesson, students should be able to summarize the properties of ionic and covalent bonds and determine the types of elements involved in each bond. 

In this update, students are watching two different videos that summarize the main ideas of the lesson. Most students should have background knowledge of covalent and ionid bonds, and this should serve as a summary and a reminder. For students that have limited knowledge, a more extensive overview on valence electrons and types of bonds. 

Students should watch the two videos on types of bonds and make a comment where they create a "bumper-sticker" slogan about one type of bond. 

Then they should read the article "Linus Pauling American Hero" and create an update on the article where they argue what they think his most important contribution to society. 

Update 2

For the Student

By the end of this lesson, you will be able to identify the properties of ionic, covalent, and metallic bonds by completing the following lab activity. 

TYPES OF BONDS LAB ACTIVITY

After completing the activity, research the types of bonds present in each of the substance and complete the knowledge survey. The knowledge survey covers properties of ionic, covalent, and metallic bonds. You should use the results of your lab activity and information learned in Update 1 to complete this survery.

Comment: What substances were the most difficult to identify and what properties were not easy to distinguish.

For the Teacher

By the end of this lesson, students will be able to identify the types of bonds present in different substances by analyzing the properties of the molecules. 

In this activity, students will work in groups to perform a series of tests on materials. Based off the results of the tests, students will then determine if the bonding present is either ionic, covalent, or metallic. 

For this lesson, it is important that students are able to directly observe the substances to apply their knowledge. To adapt to an online course, the instructor could create a video for the students to watch that covers the same procedure and allows students to observe the properties over video. 

After the lab, students should take a knowledge survey about the properties of ionic, covalent, and metallic bonding. 

Finally, students will comment on which substance was most difficult to identify and what properties were not easy to distinguish. 

Update 3

For the Student

By the end of this lesson, you should understand how to name and write the formulas of binary covalent compounds. 

For this activity, you should work in groups of 3 to 4 to complete the following activity

Naming Molecular Compounds

Make sure you work as a group and discuss each response. When you reach a stop sign, get the attention of the instructor before you move on.

When finished watch the following video: 

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Comment: Look at the ingredients on some household items. Find a binary covalent compound in the ingredient list and write the name, formula, and product that it is in. Why is naming molecular compounds an important skill? 

For the Teacher

By the end of this lesson, students will be able to name and write the formulas for binary covalent compounds. 

In this lesson, students should work in groups of 3 to 4 to complete the Naming Molecular Compounds Activity. Although the activity is not based in technology, it requires students to create their own meaning from images, tables, and diagrams.

These activities are part of a science series of lessons called POGIL. POGIL is an acronym for Process Oriented Guided Inquiry Lesson. These activities are student-centered, group learning instructional strategy where students work in small teams with the instructor acting as a facilitator. The activities are designed to follow a guided learning inquiry cycle. Through this approach, the student first explore a topic through questioning. Afterwards, concept invention takes place where students see patterns and relationships in data and vocabulary is introduced. Finally, students are asked to apply the concept to new situations. These activities are designed to help the students develop content mastery through student construction of their own understanding and to help students improve communication, critical thinking, problem solving and metacognition.

This video gives a brief explanation of POGILS used in science classrooms.

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During this activity, there are multiple checkpoints built-in, where the instructor should check in with the groups to make sure that the teams understand the material up to that point, answer any questions, and clear up any misunderstandings.

After the activity, students should look at household items and find an example of a binary molecular compound. In a comment, they should write the name, formula, and product that the substance is in. 

Update 4

For the Student

Gilbert Newton Lewis: The chemist who discovered the covalent bond and created the Lewis dot structure method of depicting molecules.

The structure of molecules plays a role in determining how molecules will interact with each other and the properties of molecules. A Lewis Structure is a simple representation of the shape of a molecule. Drawing simple representations of molecules can help visualize and predict the actual structure of the molecule. 

By the end of this lesson, you will be able to draw Lewis Structures for simple molecular compounds. 

Watch the following video and complete the tutorial found at the website below. Take notes as you go on the steps involved in drawing Lewis Structures. 

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Lewis Structure Online Tutorial

After you have taken notes, work in small groups to draw Lewis structures for the following compounds.

Check with your instructor to make sure they are correct. 

Create an Update: Create a video tutorial where you draw and explain how to draw a Lewis Structure for a compound of your choosing. 

For the Teacher

By the end of this lesson, students will be able to correctly draw Lewis structures for simple molecules. 

Students will watch a video and take notes on a website before practicing in groups drawing lewis structures for various molecules.

They will then create a video tutorial where they explain how to draw a lewis structure for a molecule. 

Update 5

For the Student

By the end of this lesson, you will understand how the three dimensional shape of a molecule is determined using VSEPR Theory and why knowing the three-dimensional shape of a molecule is important. 

The shapes of molecules determine many of the properties of substances. It is important to not only understand the simple organization of molecules but also the three-dimensional shape. Watch the video available at this link:

Comment: A symmetrical 2-D structure does not mean there is a symmetrical 3-D structure. Give an example to correspond with this statement. 

Create a Work: You will need to research a molecule of your choice and explain how the shape of the molecule plays a role in its properties. Ideas of molecules to research include ingredients in medicine, immunizations, scents, or food. Your work should be at least 1500 words in length and include at least 3 multimedia elements. 

Once you submit your first draft, you will conduct a peer review of 2 other students papers. Give your peers constructive feedback on how they could improve their paper. After the papers are reviewed, you will be able to incorporate your peer's suggestions, edit you paper, and submit a final work for a grade

For the Teacher

By the end of this lesson, students will be able to understand how VSEPR theory is applied and why knowing the three-dimensional shape of a molecule is important. 

In this lesson, students will watch the video to gain an understanding of how the shape of molecules are important in determining the properties and function of the molecules. 

Students will then create a work where they research a molecule of their choice and explain how the shape of the molecule plays a role in its properties. Ideas of molecules to research include ingredients in medicine, immunizations, scents, or food. The work shouls be at least 1500 words in length and include at least 3 multimedia elements.

 

Update 6

For the Student

By the end of this lesson, you will be able to identify the three dimensional shape of a molecule by using VSEPR theory and Lewis Structures. 

Go to the following website: 

https://phet.colorado.edu/sims/html/molecule-shapes/latest/molecule-shapes_en.html

Here you should work with a peer to complete the following chart. 

Patterns exist in geometries, so once you know the geometry of CH4 , you know the geometry of CF4 , CBr4 , CI4 , NH4 +, etc. For the molecules listed, brainstorm other molecules that would have the same geometry.

Comment: What patterns did you notice while using the simulation? Were there any exceptions that did not fit in with the patterns? Describe some general rules for determining the shape of molecules based off any pattern you observed. 

For the Teacher

By the end of this lesson, students will be able to visualize and identify the three-dimensional shape of molecules using an online simulation. 

Students should go to the following website: https://phet.colorado.edu/sims/html/molecule-shapes/latest/molecule-shapes_en.html

Students should use the simulation to complete a chart that asks students to draw the Lewis Dot Structure, 3-D Sketch, # of Electron Densities, # of Lone Pairs, and Molecular Geometry for a variety of molecules. 

Afterwards, they will create an comment in which they identify patterns in the shapes.  Emphasize to students the fact that patterns exist in geometries, so once you know the geometry of CH4 , you know the geometry of CF4 , CBr4 , CI4 , NH4 +, etc. For the molecules listed, have students brainstorm other molecules that would have the same geometry.

 

Update 7

For the Student

By the end of this lesson, you will be able to determine the polarity of molecules and the intermolecular forces present between different molecules. 

This first video explains what intermolecular forces are and how they affect the properties of matter. 

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This next video explains the difference between polar and non polar molecules. 

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And finally, this video explains the different types of intermolecular forces that occur between non-polar and polar molecules. 

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To determine the intermolecular forces present between molecules, you must first classify the molecule based off its type of bond and its polarity. 

The first classification is whether the molecule is covalent or ionic. Recall that ionic molecules are a combination of a cation and an anion. The common cations are either a metal or ammonium ion (NH4+). The common anions are nonmetals or combinations of nonmetals. On the other hand, covalent compounds are combinations of nonmetals only. Remember that hydrogen (H), regardless of its position on the periodic table, is always a nonmetal.

Covalent compounds are then classified as either polar or nonpolar. Determination of polarity often requires drawing the Lewis structure and determining the molecular shape.

Hydrogen bonding occurs in molecules where hydrogen is covalently bonded to an oxygen, nitrogen, or fluorine atom. This can be determined from the Lewis structure. Polar covalent molecules have dipole-dipole forces. Nonpolar covalent molecules have London dispersion forces

Dispersion or London forces are found between ALL molecules. This is the weakest type of intermolecular force. To understand London dispersion forces, think of the electrons in a molecule as a constantly changing cloud. In a non-polar molecule, on average the electrons are distributed equally over the molecule, but occasionally one side or the other will gain a small excess of electron density. When this occurs, the molecule has a temporary dipole. This means that one side of the molecule has a slight + charge, the other a slight - charge.

When another molecule approaches the first, it can feel this dipole. The electrons around the second molecule can then rearrange so that there is a favorable interaction between the two molecules.

Dipole-dipole forces exist between polar regions of different molecules. The presence of a dipole means that the molecule has a partially positive end and a partially negative end. Opposite partial charges attract each other, whereas like partial charges repel.

Hydrogen bonding, as the name implies, involves hydrogen. The hydrogen atom must be bonded to either an oxygen atom or a nitrogen atom. Hydrogen bonding is significantly stronger than a "normal" dipole-dipole force and is very much stronger than London dispersion forces (very weak and short-lived attractions between molecules that arise due to the nucleus of one atom attracting the electron cloud of another atom).

After watching the videos, work in small groups to complete the activity described below. 

Collect the following materials: droppers, a penny, water, ethanol, and hexane.

Take a clean dry penny and place it so the “tails” side is up.

Choose one liquid and carefully add drops to the penny. Be sure to count the drops.

Record the maximum number of drops the penny holds in a data table.

Wipe the penny and dropper dry.

Repeat this process with the other liquids. Save water for last.

It is very important that you use the SAME penny and dropper for each of the substances tested.

Create a data table and record the number of drops of liquid that the penny holds.

Comment: Which substance had the most drops stay on the penny? Why?

Update: Create an update where you draw the Lewis structure for one of the molecules above. Describe the intermolecular forces present for the molecule and how that affected the surface tension of the liquid. Apply this theory to another household substance of your choosing. Ideas could be food items, cosmetics, pr liquids found in a garage. What is the substance and what types of surface tension do you predict it to have?You may upload a video explanation or create a written explanation. 

Respond: Respond to 2 other students' updates. Comment on their choice of household item and if you agree or disagree with thier prediction. 

For the Teacher

By the end of this lesson, students will learn  to determine the polarity of molecules and the intermolecular forces present between different molecules.

In the first part of the lesson, students will watch a series of videos and read a text that describes intermolecular forces, polarity of molecules, and the different types of intermolecular forces. 

After watching the videos and reading the text, students should work in small groups to complete a short lab activity where they test the surface tension of three different substances. They will then analyze their data to determine the types of intermolecular forces present in each of the molecules. 

 

Update 8

For the Student

By the end of this lesson, you will be able to synthesize what you have learned in this learning module to create an explanation as to how molecules that are made of the same elements can have different properties.

Today you will take a look at 15 different molecules that interact with your nasal receptors and help you to smell. Their shape determines which receptors they interact with, causing you to smell different classes of molecules in different ways. As the molecule interacts with the receptor a signal is sent to the brain. In the brain, the signal is interpreted as a specific smell.  

Most organic molecules are largely made of carbon (C) and hydrogen (H) atoms. So scientists often draw the organic molecules in a short‐hand version where the carbon atoms are inferred by the points of lines and shapes.

As you walk around the lab, describe the smell for each oil. Try and make predictions on what each of the scents are before looking. 

Odor Structure Family
1. Vanilla
Aldehyde
2. Cinnamon
Aldehyde
3. Almonds/Cherry
Aldehyde
4. Wintergreen
Ester
5. Pineapple
Ester
6. Banana
Ester
7. Orange
Terpenes
8. Lemon
Terpenes
9. Pine
Terpenes
10. Rose
Alcohol
11. Thyme
Alcohol
12. Peppermint
Alcohol
13. Ginger
Ketones
14. Spearmint
Ketones
15. Caraway
Ketones

Discuss with your classmates the similarities and differences between each of the molecule drawings. 

Update: Create an update where you describe how molecules that are made of the same elements have different properties. Make sure you discuss the shapes of molecules, the polarity, and the intermolecular forces. 

Respond: Respond to two other students' updates. Is there any information that would be enhance their response? Add it here. 

For the Teacher

 

At the end of this lesson, students will be able to apply what they know about covalent compounds, Lewis structures, shapes of molecules, polarity, and intermolecular forces to describe how molecules that are made from the same elements can have different properties.

They will complete an activity in which they smell different samples of essential oils and analyze their molecular structure and shape.

They will then create a update where they describe how molecules that are made of the same elements have different properties.