Molecular Geometry: (SAM) Introduction to Molecular Shape

Interactive, scaffolded model

Overview and Learning Objectives

This unit focuses on how electron repulsions influence molecular shape. Both the electronic geometries and resulting molecular shapes will be discussed with emphasis on shared and unshared electron pairs as defining factors in the observed shape of a molecule.

Students will be able to:

• Explain that the three dimensional shape of a molecule is dependent on interactions of electrons including, repulsion to other electrons and attraction to nuclei.

• Recognize linear, trigonal planar and tetrahedral molecule shapes based on areas of electron density.

• Explain how both shared and unshared electrons (as represented in Lewis Dot diagrams) influence a molecule’s geometry and use this knowledge to predict the 3D shape of a molecule.

• Differentiate between electron geometry and molecular geometry.

• Apply their understanding of small molecule geometry to larger molecule such as fatty acids.

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Classroom Practice

Teacher's Guide:

http://sam.concord.org/publications/teacher-guides/molecular_geometry.ver6.pdf

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Central Concepts

Key Concept:

Repulsions between electron pairs around a central atom work to distribute the electrons and determine the geometry of a molecule.

Additional Related Concepts

Physics/Chemistry

• Covalent bonds
• Electron

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Extensions and Connections

Fermi Lab's ARISE Project suggests the following enhancement to this SAM unit: http://www.concord.org/~barbara/SAM/ARISE/ARISE_SAM_molecular_geometry.pdf

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Activity Credits

Created by CC Project: SAM using Molecular Workbench

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