polarity - casey souders - homecsouders.weebly.com/uploads/6/3/7/8/6378620/polarity...polarity c....

Polarity

C. Souders- Battlefield

Standard of Learning

SOL CH.3 d: The student will demonstrate an understanding of various bonding processes and the properties associated with each.

Essential Question(s)

How are chemical bonds classified? How does the bond type affect properties? How are electron dot diagrams used to represent compounds?

Unit: Bonding Lesson: Polarity Time Frame: 120 minutes (1.5 blocks)

PWCS Standards Based Planning Process

Standards: What will students know and be able to do? Essential Understandings -

Many chemical bonds can be classified as ionic or covalent. Covalent bonds may be either polar or non-polar. The bond type can be determined using the concept of

electronegativity and the values computed on the basis of differences of negativities of the involved atoms.

Compounds have various properties depending on bond type.

Essential Skills �–

Use an appropriate electronegativity chart to predict the kind of bond formed between two atoms.

Based on the values obtained predict the polar nature of any covalent bond that

may be formed. Based upon the bond types formed in a compound, predict the physical

properties of the compound with respect to selected properties such as conductivity, boiling point, freezing point and any chemical properties that affect is ability to undergo reactions.

Use drawings of the Bohr model of the atom to illustrate the electron

distribution of the bonds in covalent, ionic, and polar bonds.

Use appropriate mathematical signs ( +/ -) to indicate a polar bond and/or polar molecule.

Assessment: How will the student and I know when he/she is successful?

Before Lesson (Pre-Assessment) �– This lesson follows the lesson on Lewis structures and the basics of ionic and covalent bonding. The results from the quiz on the previous lesson should give a good indication of how many students are fluent with the topic. The teacher can ask students to draw lewis structures of different elements and compounds to ensure their understanding.

During Lesson (Formative) �– Students will be building on the concept of covalent bonding and applying their knowledge of ionic bonding in this unit. This lesson causes students some difficulty because of the 3-dimensional aspect. The molecular geometry lab should help with this. It is imperative that the teacher follow students progress closely and make sure that they are not only understanding each individual concept but how they all work together.

After Lesson (Summative) �– This lesson will most likely close with a unit test on bonding. Students will be tested on their ability to distinguish between ionic and covalent bonds, identify polarity and assume 3-D structures of molecules.

Task Analysis: What knowledge, skills and level of understanding do students need to be successful with this lesson?

Pre-Assessment Data: This lesson immediately follows the lesson on Lewis structures. The ability to draw a lewis dot diagram is necessary for the success in this lesson.

o Students must be able to draw the Lewis dot diagram for elements and compounds.

o Students should have an understanding of electronegativity and its trends on the periodic table.

o Students should be able to identify the difference between an ionic and a covalent bond.

Important Vocabulary (Literacy) �–

Polarity Electronegativity (previous) Non-polar covalent bond Polar covalent bond Ionic bond (previous) Covalent bond (previous) VSEPR Theory

Skill Development and Differentiation�– Students should be coming into this lesson with a solid knowledge of Lewis dot diagrams and a good grasp on ionic and covalent bonds. Kinesthetic and visual learners should benefit from the electronegativity demonstration and Molecular Geometry Lab, as these both allow hands on interaction. Visual learners should also benefit from the Polar Bears and Penguins activity, being able to use cartoon pictures to help understand the concept. On each of the activities there is a bonus question at the end for students who may be progressing faster than the majority of the class. These questions should challenge them to think deeper into the concept and keep them involved in the activities while other students may need additional time. Students who are excelling could also be encouraged to identify molecular shapes solely by using their flashcard information instead of building each molecule.

PWCS Standards Based Planning Process (continued)

Instruction Using Inquiry Model: What learning experiences will facilitate student success?

Framing the Learning: 1. Engage �– The lesson will start with the warm-up attached. These questions should all be answered correctly before moving on with the lesson. The

teacher should give the students a few minutes to answer the questions and then go over them to make sure that they understand the correct answer. Once the definition of electronegativity is clarified the teacher will walk the students through the electronegativity demonstration. Be sure students are understanding what the tug of war rope means and what the ball signifies. After each part of the demonstration the teacher should stop the class and have someone repeat back what just happened and why.

Learning Experiences:

2. Explore �– There are two activities/labs involved in this lesson, �“Polar Bears and Penguins�” and the �“Molecular Geometry Lab.�” These two activities will help to explain the concept of polarity of a bond and of a molecule.

�“Polar Bears and Penguins�” is an activity that involves reading a comic and applying the cartoon to the concept of electronegativity and polarity. It is important for the teacher to observe students and make sure they are actively taking a part in the reading and conceptualizing the comic. The smaller the groups the more involved the students will have to be.

�“Molecular Geometry Lab�” is an activity where students will actually build a set of molecules to identify their bond polarity as well as their symmetrical polarity. It is important for the teacher to rotate around the room and help the students build the molecules with their ball and stick models. They will have problems when it comes to creating double and triple bonds, because it takes them a while to realize the holes left in the balls are either lone electrons or they need to be bonded to something. Students will also try to �“guess�” answers on their data sheet based of what they think, instead of using the building tools in front of them. The teacher needs to encourage them to build each molecule.

3. Explain �– In this lesson there is some major confusion about the 3-D shapes. This is why the lab is included, however it is not always enough. There is a PowerPoint with some of the basic information. There is also a file with VSEPR flashcards. Using these to explain the main different molecular shapes is usually helpful for students. It gives them a quick reference with all of the information about the shape. It is important that students can identify the shape from a Lewis dot diagram, which is part of the flash card information. 4. Elaborate �– There is one practice worksheet attached for this lesson. It is up to the teacher to determine the progression of the class and if they should need more practice.

If the class is moving quickly they can begin on the structures of the organic carbon chains with common functional groups. If the students need more help with the 3-D aspect of building molecules a modification of the 3-D lab could be repeated using Hershey

kisses and toothpicks. Allow the students to create their own ball and stick model key with the different color Hershey kisses and build their molecules along with them.

5. Evaluate �– There is a quiz included in the lesson to check for progress and mastery. At the end of the unit this information should also be included in a unit test.

PWCS Standards Based Planning Process (continued)

Resources: Warm-Up handout Electronegativity demonstration, teacher will need a tug-of-war rope with a ball (or something similar), the supplied element cards printed

and string to make necklaces out of them. PowerPoint to give basis of knowledge Polar Bears and Penguins PowerPoint to use along with activity, Polar Bears and Penguins (activity source

http://www.keypress.com/Documents/chemistry/SampleLessons/SmellsTG.pdf) comic book printed as a class set, and Polar Bears and Penguin Handout.

Molecular Geometry Lab handout and a class set of ball and stick models. See �‘Elaborate�’ for alternative lab equipment ideas. Polarity handout Polarity Quiz

Reflection: Based on data, how do I refine the learning experiences and/or the assessment? Analysis of Data �– This lesson is an important part of the next unit. Although mastery of this topic is preferred, a strong understanding of

bonding is necessary for future units. If a student struggles with bonding they will continue to struggle through the remainder of the curriculum. Immediate Implications �– It is important for student and teacher reflection of this unit. If mastery is not achieved the teacher should provide

guided support for the student to gain a better understanding. However, it is also important for the student to reflect on his/her participation in this unit. Did he/she build each molecule in the 3-D lab or did he/she guess on answers based on what they thought to be correct? The building of the molecules is very important for understanding and if students missed out on that they need to go back and re-build for their own understanding.

Future Planning �– This lesson will be used prior to the next unit nomenclature. A strong understanding of bonding should give students the

confidence they need to begin the next unit with a positive outlook. Because the next unit can be daunting the more positive a student feels about their current knowledge the more successful they will be.

Warm-Up

1. What is the difference between an ionic and a covalent bond?

2. Draw the Lewis dot diagram of H2O.

3. What is electronegativity?

4. Draw the electronegativity trend on the periodic table below


ENGAGE PHASE

Name: ____________________________________ Class Period: ______ Date: ________________

Warm-Up KEY

1. What is the difference between an ionic and a covalent bond?

Ionic is between metal and non-metal, covalent is between two non-metals. Ionic involves a transfer of electrons and covalent shares electrons.

2. Draw the Lewis dot diagram of H2O.

3. What is electronegativity?

Ability of an atom to attract electrons.

4. Draw the electronegativity trend on the periodic table below

Electronegativity Demo:

Materials: A short tug of war rope with a ball strung through the middle of it.

Student volunteers Metal and non-metal necklaces (made from string and cards provided)

Directions:

1. Ask for two student volunteers, try to choose two that are substantially different in size/height/sex/etc. (ex. One tall, large, male and then one short and petite female) Give the larger person the non-metal necklace and the smaller person the metal necklace.

2. As the students to �“tug�” on the rope. The non-metal is going to �‘win�’ the tug-of-war competition. Ask the students why it happened this way.

Reason: non-metal = high electronegativity and metals have low electronegativites (look at warm-up to confirm this). Because of this the electronegativity difference resulted in a transfer of electrons.

3. Now choose two students of similar characteristics. (ex. Two girls, about the same size, but once is slightly taller than the other). Both students will get a non-metal necklace. The taller person will get the non-metal element with the stronger electronegativity.

4. Ask the students to tug on the rope. The slightly larger person will hold the rope closer to them, however the smaller person will still have a grasp on it but may be leaning towards the other person.

Reason: The taller person has a higher electronegativity and therefore

will have only a slightly stronger pull on the electron, resulting on an un-equal sharing of electrons, yet still sharing.

5. Choose two people that are almost exactly the same in characteristics. (ex. Twins would be perfect! But two males, approximately same size/height/etc. will work well too). They will be the same non-metal. They will both pull on the straps equally.

Reason: This will show that the electrons are shared equally because their electronegativity is the same.

Na Cl C O F F

Polar Bears and Penguins Please see attached PowerPoint presentation titled “Polar Bears and Penguins” to edit/project.

Slide 1

Polar Bear and Penguin Activity

Source:Investigation IV �–

Smells © UC Regents, LHS Living by Chemistry, 2003.

Slide 2 Draw the Lewis Dot Structure for HCl


EXPLORE PHASE

Now look at the image below �… a. If the penguin

represents thehydrogen and the

polar bear representsthe chlorine, whatdoes the ice cream

represent?

b.Why is the chlorineatom represented by

the larger animal?

c.Why are thepenguins feet not

touching the ground?

Slide 4 With your group �…

• Read the comic book �“The Bare Essentials ofPolarity�” and complete the questions.

Slide 5

3. Define:a.Polar molecule

b.Electronegativity

c.Dipole

4. Look at the picture on the bottom of page 1.Explain how the iceberg, penguins and polarbears represent the trends of electronegativityon the periodic table.

Slide 7

5. What is happening when two penguins or twopolar bears are arm wrestling?

Slide 8

6. On page 3 there is an image of an oxygenmolecule and on page 4 there is an image of anitrogen molecule. How many scoops of icecrefam are on each and what do the scoopsrepresent?

7. On page 4 there is an image representing CO2

and one representing H2O.a.Identify similarities and differences in these twoimages.

b. What do these similarities and differencesrepresent in terms of bonds?

Slide 10

8. What does the crossed arrow represent inthe comic book?

Slide 11

9. How does polarity relate to electronegativity?

Polar Bears and Penguins Activity Pre-Activity Questions:

1. Draw the Lewis structure for HCl.

2. Answer the questions for the following image�…

a. b. c.

Comic Book Questions:

3. Define:

a. Polar molecule

b. Electronegativity

c. Dipole

4. Look at the picture on the bottom of page 1. Explain how the iceberg, penguins and polar bears represent the trends of electronegativity on the periodic table.


5. What is happening when two penguins or two polar bears are arm wrestling?

6. On page 3 there is an image of an oxygen molecule and on page 4 there is an image of a nitrogen

molecule. How many scoops of ice crefam are on each and what do the scoops represent?

7. On page 4 there is an image representing CO2 and one representing H2O.

a. Identify similarities and differences in these two images.

b. What do these similarities and differences represent in terms of bonds?

8. What does the crossed arrow represent in the comic book?

9. How does polarity relate to electronegativity?

If you are waiting for others to finish �…

10. Draw an illustration using polar bears and penguins for the molecule HF.

Molecular Geometry Lab

Linear shapes tend to be non polar if the same elements are combined. Linear shapes are polar if 2 different elements are combined. Pyramidal shapes are usually polar Bent shapes are polar Tetrahedral shapes are polar if not symmetrical, nonpolar if symmetrical Construct each of the following: FORMULA NAME # bonded

pairs # non-

bonded pairs

Shape Polarity Ball and Stick Sketch Lewis Dot Structure

H2 Hydrogen

H20 Water

CH4 Methane

Cl2 Chlorine

NH3 Ammonia

HF Hydrogen Fluoride


FORMULA NAME # bonded

pairs # non-

bonded pairs

Shape Polarity Ball and Stick Sketch Lewis Dot Structure

N2 Nitrogen

CO2 Carbon Dioxide

H2O2 Hydrogen Peroxide

O2 Oxygen

H2S Hydrogen Sulfide

1. Which molecules are non polar because all BONDS are non polar?

2. Which molecules have polar bonds but are non polar because of symmetry?

3. Why do we not represent ionic compounds with ball and stick models?

4. How does building molecular models help to determine the shape and polarity of the molecule?

Polarity

Please see attached PowerPoint presentation titled “Polarity” to edit/project. Slide 1

Slide 2

Compare the atoms electronegativity

�• Non-polar covalent bonds: when bonded electrons are shared equally

�• Ex. H2, O2, Cl2

�• Polar Covalent Bond: covalent bond when electrons are shared un-equally.

�• Ex. HCl, H2O

I use the example of divorce in familiesfor this. A non polar covalent bond isparents who share their childrenequally, one week with dad and oneweek with mom. A polar covalent bondis when parents are divorced and oneparent has custody during the weekand the other on the weekends. Yesthey are sharing responsibility, howeverit is shared un equally. And then Ionicbonds are when one parent hascomplete custody and the other parentdoes not see the children.


EXPLAIN PHASE


The higher electronegativity receives a slightly negative chargeThe lower electronegativity receives a slightly positive chargeRepresented by �• So + or -

Slide 4

H-Cl

The polarity is represented by an arrow pointing from Positive to Negative (low to high)

Slide 5 Electronegativitydifference range

Most probable type of bond

Example

0.0 �– 0.4 Non-polar covalent H-H (0.0)

0.4 �– 1.0 Moderately polar covalent

H �– Cl (0.9)

1.0 �– 2.0 Very polar covalent H �– F (1.9)

2.0 Ionic NaCl (2.1)

Valence Shell Electron Pair Repulsion Theory�• Electron pairs repel (like charges)�• Molecules change shape to make the placement

of electrons as far apart as possible.

Slide 7

Slide 8

You are responsible for �…Linearbenttrigonal planartetrahedralpyramidal

Go over each required bond withstudents, making flashcards forstudying & understanding.

Slide 10

Solid line is within the plane.Dotted line is going away from the plane.Solid wedge is coming out of plane

VSEPR Flash Cards

Sketch of the VSEPR Geometry you are describing on the opposite side Sketch of the VSEPR Geometry you are describing on the opposite side



Electron Dot

VSEPR Geometry Name &sketch

StructuralFormula Electron Dot


StructuralFormula

# lone pairs # bonded pairs # lone pairs # bonded pairs

Electron Dot




StructuralFormula


Electron Dot




StructuralFormula


Polarity

1. For each of the following identify whether the compound is ionic, polar covalent or non-polar covalent.

a. HCl

b. H2O

c. LiBr

2. Draw the electron dot structure for each molecule. Identify polar covalent bonds by assigning slightly positive ( +) and slightly negative ( ) symbols to the appropriate atoms.

a. HOOH

b. BrCl

c. HBr

d. H2O

3. For each compound in number 2, identify if the molecule is polar or non-polar based on symmetry.



ELABORATE PHASE

Polarity Quiz 1. Identify the following compounds as ionic, polar covalent or non polar covalent. If polar covalent

identify the partial positive and partial negative elements.

a. MgCl2 b. Br2 c. H2O

2. For PCl3a. Draw the dot diagram

b. What 3 D shape will it form?

c. Draw the 3 D shape

d. Identify the polar and non polar BONDS.

e. Identify whether the MOELCULE is polar or non polar.

3. For H2Oa. Draw the dot diagram

b. What 3 D shape will it form?

c. Draw the 3 D shape

d. Identify the polar and non polar BONDS.

e. Identify whether the MOELCULE is polar or non polar.



EVALUATE PHASE