Making Connections between Electronegativity, Molecular Shape, and Polarity (25 Favorites)

ACTIVITY in Polarity, Periodic Table, Molecular Structure, VSEPR Theory, Electronegativity. Last updated August 7, 2017.


Summary

In this activity, students will find the electronegativity values of a variety of elements, draw the Lewis structures of select molecules that are made with those elements, and identify the molecular shape of each molecule. Students will then be asked to determine if the molecules are polar or nonpolar based on the electronegativity values of the atoms and the molecular shape. Students will use Ptable.com to find information about atoms and molecules and connect what they find to observable properties.

Grade Level

High School

NGSS Standards

  • 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.

Objectives

By the end of this activity, students should be able to

  • Relate the shape of a molecule and the relative electronegativity values of its constituent atoms to the polarity of the molecule.
  • Describe the properties and functions of common molecules.
  • Draw Lewis structures of a molecule based on the molecular formula.
  • Identify the shape of a molecule based on the Lewis structure.

Chemistry Topics

This activity supports students’ understanding of

  • Periodic trends
  • Electronegativity
  • Molecular shape
  • Polarity

Time

Teacher Preparation: 10 minutes

Lesson: 60 minutes

Materials

  • Computer for each student or pair of students
  • Access to the internet
  • Handout for each student (either electronic or paper)

Safety

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

Teacher Notes

  • This activity is designed so that students will make connections between the concepts of electronegativity, molecular shape and polarity. Students should have been introduced to these concepts before this activity.
  • Students also need to be familiar with the Ptable.com web interface. If they have never used it before a brief overview of where to find the different tabs, how to scroll over elements to get more information, and where to find specific information would be helpful at the beginning of the activity.
  • Depending on the students’ familiarity and comfort level with Lewis structures, more complicated molecules may be substituted for those suggested here.
  • At the end of the activity, the teacher can wrap up by having students review the Lewis structures, molecular shapes, polarities, and interesting facts with the class. During this discussion, the teacher can point out any connections between the molecular properties and the interesting facts the students share.
  • An answer key document is provided and available for download for teacher reference

For the Student

Making Connections between Electronegativity, Molecular Shape, and Polarity

Objective

At the end of this activity you should be able to determine the polarity of a molecule based on the electronegativity of its constituents and its molecular shape.

Directions

Complete each of the following tasks using Ptable.com. Answer the questions as you go along.

  • Go to http://ptable.com/ in your web browser.
  • Select the “Properties” tab at the top.
  • Scroll over an element to see its electronegativity (see image below). Fill in the table below with the electronegativity values for the atoms provided. An example is provided for you.Activity connectionsusingptable screenshot1

Element

Electronegativity

C

2.55

H

Cl

Br

N

O

F

P

  • Which atom is the most electronegative? How can you tell?
  • If an atom with a high electronegativity value bonds with an atom with a low electronegativity value, what impact does the difference in electronegativity value have on the bond?
  • Draw the Lewis structures of the molecules below and determine their molecular shape:

CH4




Shape:

NH3




Shape:

CCl4




Shape:

PCl5




Shape:

HBr




Shape:

N2




Shape:

F2




Shape:

OF2




Shape:

  • Go to the “Compounds” tab on Ptable.com and find the “Name or Formula” search bar. It is circled in the image below.Activity connectionsusingptable screenshot2

Search for each of the molecules in question 6. Click the link to the molecule that matches the formula exactly. An example of CCl4 is shown below.Activity connectionsusingptable screenshot3

After you have clicked on the link, a window will pop up on the screen with information regarding the structure and function of the molecule. An example of what you should see for of CCl4 is shown below. Please note that some structures do not include lone electron pairs. Activity connectionsusingptable screenshot4

  • Look at the structure for each molecule and determine if your Lewis structure and shapes were correct. Describe any structures or shapes you had incorrect and explain why they were incorrect:
  • For each molecule, use the correct shape in combination with the electronegativity values you found in question 3 to determine if the molecule is polar or nonpolar. Describe how you know if each molecule is polar or nonpolar.

CH4

Polar or Nonpolar?

How do you know?

NH3

Polar or Nonpolar?

How do you know?

CCl4

Polar or Nonpolar?

How do you know?

PCl5

Polar or Nonpolar?

How do you know?

HBr

Polar or Nonpolar?

How do you know?

N2

Polar or Nonpolar?

How do you know?

F2

Polar or Nonpolar?

How do you know?

OF2

Polar or Nonpolar?

How do you know?

  • Read about each molecule and write down one intereacting fact about each molecule.

CH4

NH3

CCl4

PCl5

HBr

N2

F2

OF2

  • Considering differences in electronegativity values between bonded atoms and the overall molecular shape, what do nonpolar molecules have in common?
  • Considering differences in electronegativity values between bonded atoms and the overall molecular shape, what do polar molecules have in common?
  • Write a short paragraph describing how electronegativity and molecular shape determine the polarity of a molecule. In your paragraph, describe why chemists consider relative electronegativity values and not absolute electronegativity values when determining the polarity of a bond. Also explain how a molecule with polar bonds can be non-polar overall.