After learning about the concepts of electronegativity and polarity in yesterday’s lesson, students learned that scientist Linus Pauling assigned electronegativity values to individual atoms as a measure of how strongly an atom attracts electrons (click here for a deeper dive into how he calculated electronegativity).  Although not used in class, the Lesson 44 PowerPoint is provided here as a resource and includes a copy of the periodic table with electronegativity values for each element.  It also explains the difference in electronegativity between covalent bonds (0.5 and less), polar covalent bonds (between 0.5-2.1), and ionic bonds (greater than 2.1).

After practicing how to calculate bond differences as a class, students worked through the Lesson 44 Worksheet using the Electronegativity Scale and Bonding Continuum handout.

Students who finish the work early had time to complete yesterday’s Lesson 43 worksheet and Monday’s Polarity and Intermolecular Forces Gizmo.  Students who are fully caught up have the opportunity to investigate vectors and may earn bonus credit for completing one or both vector-related Gizmos.

Notes from class:

Keep Learning!

Want more information about dipoles from yesterday’s lesson?  Read about how dipole moments are calculated.

Wondering how scientists measure the electronegativity of atoms?  One new technique involves atomic force microscopy.  Read more:  Electronegativity of a single atom scrutinized under the microscope.

The Pauling scale of electronegativity was updated in a paper published a year ago (January 2019, Journal of the American Chemical Society).  Read a summary of the work: New scale for electronegativity rewrites the chemistry textbook.  Want more?  Take a look at the supporting data for the journal article.

Homework:

• Read Lesson 44 in the textbook.  Login via the Sapling website and enter your username and password.
• Write notes for Lesson 44 and work through the practice problems at the end of Lesson 44
• Please ask questions about anything from Lesson 44 you do not yet fully understand.

After completing the entry task on slide 3 of the Lesson 43 PowerPoint, we visualized the concept of a “charged wand” and it’s effect on polar molecules using a balloon, electrons gently extracted from the hair of a student volunteer, and a burette filled with water.  Students observed water flowing straight through the burette at the beginning of the demonstration, and then saw how water was attracted to the “charged wand” when the balloon was placed close to the stream of water.  Students were challenged to explain the observation using their understanding from our work yesterday (models drawn in the class notes below).  Next, we watched the Bozeman Science video below about the polarity of water molecules to review, extend, and apply the learning from yesterday to real-world scenarios:

We then talked through the definitions of electronegativity and dipole, relating both concepts back to molecules of water and carbon dioxide (see class notes below).  Finally, students received copies of the Lesson 43 Worksheet and accompanying cartoon to work through.

Notes from class:

Keep Learning!

Looking for more challenge?  When drawn as vectors, dipole arrows allow scientists to calculate the magnitude and direction of the overall dipole of a molecule.  Using vector addition, dipole arrows explain why water is polar while carbon dioxide is non-polar.  Brush up on vectors and vector addition using the Gizmo simulations.  Ask for one or both copies of the Gizmo handouts and grow your brain!

Homework:

• Read Lesson 43 in the textbook.  Login via the Sapling website and enter your username and password.
• Write notes for Lesson 43 and work through the practice problems at the end of Lesson 43
• Please ask questions about anything from Lesson 43 you do not yet fully understand.