Strong Chemical Bonds (SAM)

Interactive, scaffolded model

Overview and Learning Objectives

First, students experiment with how orbital shapes are affected by other charges and atoms. Then, students explore the role of electronegativity in bond formation by setting the electronegativities of two bonded atoms. They should see that ionic bonds form between atoms of very disparate electronegativities, and that polar covalent bonds form between atoms of somewhat disparate electronegativities, and non-polar covalent bonds form between atoms that have similar electronegativities. Finally, they will also see how a molecular surface becomes polarized when polar covalent bonds are part of a larger molecule.

Students will be able to:

• experiment with setting the electronegativity of two different atoms;
• explain the relationship between types of bonds and the electronegativity of the bonded atoms;
• explain why polar bonds form and their relationship to electron clouds as they are attracted to two different nuclei.

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Classroom Practice

The intention of this activity is that it would be run over two separate class days, so that the students would complete Part 1, then have a class discussion, perhaps revisiting some of the key models together via an LCD projector or smart board, and then complete Part 2 the next day. Having students complete the entire computer based activity in one sitting is not recommended.

Prerequisite: Because students explore the formation of chemical bonds using atoms that depict electrons in orbitals instead of orbits, it would be helpful if they had some understanding of basic atomic structure and concept of a simple orbital. There are also several representations of molecules in this activity, so understanding that molecules can be visualized in various ways, yet still be the same molecule, will also be a benefit.

The last part of the activity connects the idea of polarity to the properties of various amino acids. While not necessary, if the students were already familiar with the idea that a protein is linked chain of amino acids, it would be beneficial.

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Central Concepts

Key Concept:

The type of bond formed -- ionic, non-polar covalent, or polar covalent -- depends on the electronegativity of the two atoms that are bonded together.

Additional Related Concepts

Concept Map Available

Molecular Biology

• Polar molecules
• Polar nature of water

Physics/Chemistry

• Bonds
• Covalent bonds
• Dipole
• Electron
• Electronegativity
• Ionic bonds
• Molecule
• Van der Waals

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Textbook References

• Biology (Prentice-Hall) New York Edition - Chapter Eight: Photosynthesis
• Biology (Prentice-Hall) New York Edition - Chapter Two - The Chemistry of Life
• Biology: Concepts and Connections (Pearson) 5th Edition - Chapter 2: The Chemical Basis of Life
• BSCS Blue (8th Edition) - Chapter 1: The Chemistry of Life
• Cell Biology (Pollard and Earnshaw) Saunders 2002 - Chapter Three: Basic Biophysical Concepts

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Benchmarks and Standards

AAAS

• THE PHYSICAL SETTING: THE STRUCTURE OF MATTER - Atoms often join with one another in various combinations in distinct molecules or in repeating three-dimensional crystal patterns (Full Text of Standard)
  
  
• THE PHYSICAL SETTING: THE STRUCTURE OF MATTER - The configuration of atoms in a molecule determines the molecule's properties (Full Text of Standard)
  
  

NSES

• Physical-Science: Matter Structure/Properties - 1 Atoms interact with one another by transferring or sharing electrons (Full Text of Standard)
  
  
• Physical-Science: Matter Structure/Properties - 3 Bonds between atoms are created when electrons are paired up (Full Text of Standard)
  
  

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Extensions and Connections

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Macro Micro Link

By understanding the different types of bonds that can form, many physical properties can be understood, including boiling point and solubility.

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Activity Credits

Created by CC Project: Molecular Logic using Molecular Workbench

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Requirements

• Adobe Flash Plugin
• Java 1.5+ - Java 1.5+ is available for Windows, Linux, and Mac OS X 10.4 and greater. If you are using Mac OS X 10.3, you can download MW Version 1.3 and explore within it instead.
• QuickTime for Java - Important Note: Due to a recent QuickTime update, you may not be able to see some models with embedded Flash components. We are currently trying to develop a workaround.

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