Bond Polarity and Determining Molecular Geometry

Learning Resource Type

Lesson Plan

Subject Area

Digital Literacy and Computer Science

Science

Grade(s)

9, 10, 11, 12

Overview

In this lesson, students will examine the electronegativities of atoms relative to one another to determine if a covalent bond will be classified as polar or nonpolar. Students will use an online simulation to help them understand the importance of lone pairs of electrons as well as bonding pairs of electrons. Students will use ball-and-stick models to examine and identify the shapes of various molecules.

This lesson results from a collaboration between the Alabama State Department of Education and ASTA.

Science (2015) Grade(s): 09-12 - Chemistry

SC15.CHM.3
Use the periodic table as a systematic representation to predict properties of elements based on their valence electron arrangement.

Vocabulary

Protons
Neutrons
Nucleus
Electrons
Valence
Main group elements
Properties
Atoms
Elements
Periods/ Rows
Groups/ Families/ Columns
Atomic/ molecular level
Macroscopic level
Periodic trends
metal/ nonmetal/ metalloid behavior
electrical/ heat conductivity
electronegativity
electron affinity
ionization energy
atomic-covalent/ ionic radii
Molecular modeling
Lewis dot
3-D ball-and-stick
space-filling
VSEPR
Types of bonds
ionic bonds
covalent/ molecular bonds
metallic bonds
Molecular shapes
Ions
Ionic compounds
Covalent/ molecular compounds

Knowledge

Students know:

The atom has a positively-charged nucleus, containing protons and neutrons, surrounded by negatively-charged electrons.
The periodic table can be used to determine the number of particles in an atom of a given element.
The relationship between the arrangement of main group elements on the periodic table and the pattern of valence electrons in their atoms.
The relationship between the arrangement of elements on the periodic table and the number of protons in their atoms.
The trends in relative size, reactivity, and electronegativity in atoms are based on attractions of the valence electrons to the nucleus.
The number and types of bonds formed (i.e. ionic, covalent, metallic) by an element and between elements are based on the arrangement of valence electrons in the atoms.
The shapes of molecules are based on the arrangement of valence electrons in the atoms.
The rules for naming chemical compounds are based upon the type of bond formed.
The number and charges in stable ions that form from atoms in a group of the periodic table are based on the arrangement of valence electrons in the atoms.

Skills

Students are able to:

Predict relative properties of elements using the periodic table.
Predict patterns in periodic trends based on the structure of the atom.
Predict patterns in bonding and shape based on the structure of the atom.
Use the periodic table to determine how elements will bond.

Understanding

Students understand that:

Models are based on evidence to illustrate the relationships between systems or between components of a system.
Each atom has a charged substructure consisting of a nucleus, which is made of protons and neutrons, surrounded by electrons.
The periodic table arranges elements into periods/ rows by the number of protons in the atom's nucleus.
Elements with similar properties are placed into groups/ families/ columns based on the repeating pattern of valence electrons in their atoms.
Attraction and repulsion between electrical charges at the atomic scale explain the structure, properites, and transformations of matter, as well as the contact forces between material objects.
The attraction and repulsion of charged particles in the atom creates patterns of properties of elements.
The arrangement of valence electrons in an atom also creates patterns of properties of elements.
Elements form bonds based upon their valence electron arrangement.
Chemical compounds are named based upon the type of bonds formed by their constituent atoms/ ions.
Different patterns may be observed at the atomic/ molecular level and the macroscopic level.

Scientific and Engineering Practices

Developing and Using Models; Analyzing and Interpreting Data

Crosscutting Concepts

Patterns; Systems and System Models; Structure and Function

DLCS18.HS.25

Primary Learning Objectives

The student will distinguish between bond types including ionic bonds, polar covalent bonds, and nonpolar covalent bonds.
The student will use a model to predict the type of bonding and shape of simple compounds.
The student will determine how electronegativity and electron density determines if a covalent bond is polar or nonpolar.

Procedures/Activities

Before:

Have students pick a partner in the classroom and pretend that their partner is their twin sibling. Have students assume that they are nearing their 16th birthday and that their parents are requiring them to share a car.

Have students brainstorm ways that they could share the car. Hold a classroom discussion to identify the different ways the car could be shared. Be sure that the following explanations arise in the discussion:

The car could be shared 50/50 where each sibling gets the car for the same amount of time each week.
The car could be shared based on need so the sibling that has more extracurricular activities or events gets the car for a larger percentage of the time; the car is shared unequally.
One sibling could take complete control of the car and not share at all with the other.

Relate the ways that the twins can share the car to the way two atoms can share (or transfer) electrons. Use the Image of Bond Types from UC Davis ChemWiki for visualization.

If the twins share 50/50 then the car spends equal time with each twin similarly to in a nonpolar covalent bond where electrons are evenly distributed around both (or all) atoms. Emphasize that the prefix co- (in covalent) means to share and give examples such as the co-captain of a team.
If the twins share the car depending on who needs/wants the car the most they are sharing unequally. Since electrons are still being shared this is still a covalent bond, however, the unequal distribution makes the bond polar covalent. Ask students what they know of that has poles and encourage them to think about the north/south poles of the earth. Describe that the earth is polar because it has 2 distinct poles (north and south) and polar covalent bonds are polar because they also have 2 distinct poles (positive and negative).
In the case that one twin takes complete control of the car, discuss the comparative strengths of the twins. The one with the most strength (the most electronegative) will take complete control of the car. This is similar to an ionic bond. Emphasize the "i" in ionic and remind students that generally "i" is selfish so the electrons are being completely taken by one of the atoms and not being shared at all. Encourage students to think of why this is still considered a bond and not called an ionic transfer (the positive and negative charges that result from the transfer attract one another holding the ions together).

During:

Students will complete "Dipoles and Bond Polarity pHet Activity" worksheet with their partner using the pHet website to develop a rule for determining if a molecule is polar or nonpolar. Be certain to discuss the role and importance of lone pairs of electrons.
Students will be assessed using a Jigsaw Cooperative Learning strategy.
Assign each group a set of questions from the student activity worksheet that they will be responsible for sharing the correct answers with the class. After the individual groups complete the activity the class will come together for a discussion and each group will be responsible for discussing their assigned question(s).
Students will complete Alabama Science in Motion (ASIM) activity Molecular Shape and Polarity using 3-D ball and stick model kits and VSEPR Geometries Chart to determine the shape and polarity of various molecules.

After:

Allow students to individually access the Intermolecular Forces: Review to reinforce calculating number of lone pairs of electrons, bonding pairs of electrons, and molecular geometry to review. To assess student mastery the teacher will actively walk around the room and check individual student work before students leave.

Assessment Strategies

The student will be assessed on their completion of "Dipole and Bond Polarity pHet Activity" worksheet as a group using the jigsaw approach where each group will be responsible for completing the sheet on their own and then sharing the answers to assigned questions with the class.
The student will be assessed on completion of Molecular Shape and Polarity chart from ASIM.
The student will be assessed on individual completion of the Intermolecular Forces: Review website by the teacher walking around the room and checking individual progress before students leave.

Acceleration

Students who are already familiar with polarity and molecular shape can use the pHet activity: Molecule Shapes to look at the bond angles for the different shapes.

Intervention

Students who do not reach mastery on their individual assessment will be pulled for individual or small group instruction drawing molecules on small dry erase boards and discussing molecular arrangement with the teacher.

Total Duration

91 to 120 Minutes

Background/Preparation

Prior to this lesson, students should have some knowledge on periodic trends, specifically electronegativity.
Students should also be comfortable with drawing Lewis structures.

Materials and Resources

Technology Resources Needed

Image of Bond Types from UC Davis ChemWiki

VSEPR Geometries Chart (can be downloaded and printed for student use)

pHet Simulation on Molecule Polarity

ASIM: Molecular Shape and Polarity

pHet Simulation on Molecule Shape (for acceleration strategy)

Approved Date

2016-08-17