Bonds: The Basis For Biology

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Objective

SWBAT determine if a chemical reaction will result in an ionic or covalent bond based on the location of the elements on the periodic table.

Big Idea

No more guessing! Students will utilize the periodic table and their understanding of atoms to predict the types of bonds that will form during simple chemical reactions.

Lesson Introduction: Bonding With Your Students

1 minutes

The video clip provides an introduction and rationale for this lesson reviewing types of chemical bonds.  

The students currently enrolled in my Biology College Prep class have already been introduced to this content in their 8th grade Physical Science classes, so I use this lesson as a review of their extensive study last year.  If your students have not had this content before, I suggest splitting up the content over two days with Ionic Bonds on the first day and Covalent Bonds on the second.  Another strategy to reinforce this concept is to use pre-made or teacher-made manipulatives for students to use in an effort to visual the movement of electrons to form these types of bonds, thus forming new compounds through chemical reactions.

Hook - Bonds Are Everywhere

5 minutes

Students will watch this video clip and then create a Venn diagram to compare and contrast ionic and covalent bonds.  Students will share their responses with their neighbor.  As a check for understanding, each group will give a summary statement to the class explaining either the similarities or differences between ionic and covalent bonds.  

Student Work - Types of Bonds Comparison - After analyzing the student responses, most of the students are able to explain the movement of electrons in ionic (give up or receive) and covalent (share) bonds, but it seems many students missed the rationale as to why certain elements form which type of bond.  A point of emphasis should be that ionic bonds form between one nonmetal element and one metal element while covalent bonds from between two nonmetal elements.  

Direct Instruction - Bonds: The Building Blocks Of Life

25 minutes

Students will get out a sheet of paper and title it, "Lecture Notes: Chemical Bonds".  The lesson's power point lecture notes  will build off of the students understanding of the arrangement of the periodic table and atomic structure.  By conceptualizing the number of valence electrons in an atom, students are able to predict which elements can create chemical bonds to complete the outer energy level using the octet rule to make the molecule chemical stable.  The students will be referred to models of the atomic structure, the types of bonds, and the periodic table throughout the lesson.  

Sample of Student Work - Lecture Notes - Types of Bonds  By this point in the year, the students have come to realize that the lecture notes reveal the content of future tests so they will give their best effort to record a majority of what is discussed in the presentation.  Students are encouraged to take their notes in any format that supports their study habits and makes it easier to review.

The lecture notes will focus the students' attention on ionic, covalent, and metallic bonds.  

Guided Practice - Covalent Bonds: Sharing Is Caring

10 minutes

Students will work with their neighbor to complete the Covalent Bonding Practice Worksheet.  Experience proves that students have a more difficult time conceptualizing the model of single, double, and triple covalent bonds so it is recommended to have the students work in pairs to gain confidence through collaboration.  Remind students that covalent bonds only occur between two non-metals!

Remind students to complete each sample problem with these steps:

  1. Write the chemical symbol for each element in the sample problem (leave enough space!)
  2. Diagram the number of valence electrons filling in one on each side of the imaginary square around the chemical symbol. Once there are four electrons filled in, continue to pair up the electrons.  Any unpaired electrons have the potential to participate in the chemical bond.
  3. Identify any remaining unpaired electrons on all atoms in the sample problem.
  4. Determine how many bonds will be needed to complete the octet for each atom.
  5. Draw in the bonds on your models and determine if each atom has the equivalent of eight electrons in either paired or bonded valence electrons.

Once the students get the hang of the process, sample covalent bonds seem like a riddle trying to pair up the electrons to make the chemical compound stable and the valence shells full.

Sample of Student Work - Covalent Bonds The samples of student work that were randomly collected demonstrate the wide range of mastery for this topic. The first student's sample work reflects a strong understanding of the topic, but made a critical error modeling the water molecule that was reviewed in class.  This type of error seems common with 9th grade students and is attributed to a lack of concentration and attention because the student really had mastered the content!

Please view the Lesson Reflection for more insight regarding student mastery of this concept!

 

 

Independent Practice - Bonds: Isn't It Ionic

10 minutes

Now that the students have worked with their neighbor solving the Covalent Bonding Practice Worksheet, it is time to use the lecture notes and collaborative confidence to complete this next activity on their own.  Remind students that ionic bonds occur between a metal and a non-metal.  Students will work to complete the Ionic Bonding Practice Worksheet. Students are reminded of the following steps when solving the sample problems:

  1. Write the chemical symbol for each element in the sample problem (leave enough space!)
  2. Diagram the number of valence electrons filling in one on each side of the imaginary square around the chemical symbol. Once there are four electrons filled in, continue to pair up the electrons.  Any unpaired electrons have the potential to participate in the chemical bond.
  3. Identify any remaining unpaired electrons on all atoms in the sample problem.
  4. Determine if the atom is going to give up (metals) or receive (nonmetals) the electrons during the formation of the ionic bond.  
  5. Draw in the arrows on your models to represent the transfer of electrons from one atom to the next. 
  6. To check for accuracy, count to determine if each atom has eight electrons or an outer valence shell.

The class will review the correct solutions when all of the students have had time to complete their models of ionic bonds.  Student volunteers will be given the opportunity to come to the front board to sketch their ionic bond models and provide a narration to explain the transfer of electrons.

Sample of Student Work - Ionic Bonds - Analysis of the student work for this activity revealed that students either mastered the concept of ionic bonds or completely struggled!  After further investigation, students who were struggling with drawing the models of ionic bonds did not understand how the number of valence electrons for each element related to the concepts of chemical bonds.  By going back to review how to determine the number of valence electrons and the energy levels of electrons, students were able to refocus and start fresh.  By the end of the lesson, more students were successful with the ionic bonding models and were even able to assist their peers with comprehending the concept.   

 

 

Close: Predictions Using The Periodic Table

5 minutes

With five minutes remaining in the class session, students will bring their attention back up to the front board for a final check for understanding.  Students will need to determine which type of bond is created between the sample elements and sketch the correct model for the chemical bond that will form.  Students should be reminded that most of the time atoms chemically combine in ratios that are more complicated than 1:1, so encourage students to stretch their understanding and go beyond the simple solutions!

  1. Lithium and Chlorine  =  Li   +  Cl 
  2. Carbon and Oxygen   =  C +   O
  3. Sodium and Chorine  =  Na  +   Cl  
  4. Chlorine and Oxygen  =  Cl  +   O

At the conclusion of the final activity, student volunteers will share the type of bond created for each sample question, as well as the final balanced chemical equation.  If students did not complete either the Ionic Bonding or Covalent Bonding Practice Worksheets, they will need to finish them as homework to ensure all students have had ample practice with both types of chemical bonding models.