UTPA STEM/CBI Courses/Organic Chemistry/Molecular Shapes

Course Title: Organic Chemistry I

Lecture Topic: Molecular Shapes

Instructor: Hari D. Mandal

Institution: TAMIU

Backwards Design

Course Objectives

• Primary Objectives- By the next class period students will be able to:
  • Understand the concept of Lewis structures.
  • Identify the valence electrons.
  • Understand the various structural formulas of organic compounds.
  • Understand valence shell electron pair repulsion (VSEPR) theory.
  • Understand the geometric shapes of molecules based on VSEPR.
  • Understand the concept of hybridization and its relationship with the molecular shapes.

• Sub Objectives- The objectives will require that students be able to:
  • Identify valence electrons.
  • Identify the lone-pair and bond-pair electrons.
  • Draw Lewis structures of various molecules.
  • Use VSEPR to determine electron domain geometry and actual geometry of molecules.
  • Draw the of s and p atomic orbitals correctly.
  • Draw the sp, sp2, and sp3 hybrid orbitals correctly.
  • Draw and understand the overlapping of orbitals leading to covalent bonds

• Difficulties- Students may have difficulty:
  • Identifying the difference between the electron domain geometry and actual geometry of a molecule.
  • Understanding the formation of covalent bonds between hybrid orbitals and between atomic orbitals.
  • Understanding the relationship between the hybrid orbitals and molecular shapes.
  • Understanding the orbital overlapping leading to bonds.

• Real-World Contexts- There are many ways that students can use this material in the real-world, such as:
  • Molecular shape is a fundamentally important feature that often determines the fate of a compound in terms of molecular interactions with preferred and non-preferred biological targets.
  • Complementarity of binding in small molecule-protein, peptide-receptor, antigen-antibody and protein-protein interactions is key to life and survival, but also to targeting molecules with bioactivity.
  • Molecular shapes plays a key role in the senses: smell (via hundreds of olfactory receptors), sight (via receptors responsible for the perception of color), and taste (via receptors responsible for the perception of bitter, sour, sweet, and salt)

Model of Knowledge

• Concept Map
  • Write electron configurations of common elements.
  • Identify the valence electrons.
  • Draw Lewis structures.
  • Apply VSEPR and determine the electron domain geometry.
  • Determine the molecular geometry.
  • Describe the hybridization of the molecule that fits the geometry.

• Content Priorities
  • Enduring Understanding
    • Predict the shapes of the molecules without any lone-pair electron.
    • Predict the shapes of the molecules that contain lone-pair electrons.
    • Know the difference between the bond-pair and lone-pair electrons.
    • Know the effect of lone-pairs on the overall shape of the molecules.
  • Important to Do and Know
    • Common bond angles in organic compounds are usually close to 109°, 120°, or 180°.
    • Common shapes: linear, trigonal planar, tetrahedral, etc.
    • These bond angles and the shapes of the molecules cannot be explained with simple s and p orbitals.
    • To explain the shapes of molecules, we assume that the s and p orbitals combine to form hybrid atomic orbitals that separate the electron pairs more widely in space and place more electron density in the bonding region between the nuclei.
  • Worth Being Familiar with
    • Hybridization is the concept of mixing atomic orbitals into new hybrid orbitals suitable for the pairing of electrons to form chemical bonds.
    • Hybrid orbitals have different energies and shapes than the component atomic orbitals.
    • Hybrid orbitals are useful in the explanation of molecular geometry and atomic bonding properties.

Assessment of Learning

• Formative Assessment
  • In Class (groups)
    • Students will draw Lewis structures of some assigned molecules.
    • Count the number of bond-pair and lone-pair electrons.
    • Predict the shapes of the molecules based on the VSEPR model.
    • Compare the shapes and hybridization of each molecule.
  • Homework (individual)
    • Assigned homework problem from text or created by the instructor.
• Summative Assessment
  • Students will be given exam based on the topic in the class.
  • One or more students solve problems on the white board..
  • Predict the shapes of the molecules based on the VSEPR model.
  • Compare the shapes and hybridization of each molecule.

Legacy Cycle

OBJECTIVE

By the next class period, students will be able to:

• Understand VSEPR theory
• Understanding various geometric shapes of common molecules.
• Understanding electron domains and how they are used to predict molecular geometry
• Understand how to predict molecular geometry

The objectives will require that students be able to:

• Determine electron domains and use this knowledge to develop electron domain geometries and this can be used to understand what bond angles are possible and why there are different set bond angles.
• Use the knowledge of electron domain geometries to predict molecular geometries.

THE CHALLENGE

To develop three dimensional molecular model using chemistry model kit or everyday household objects.

GENERATE IDEAS

Different groups develop different ideas for various objects that can be used to construct molecular models.

MULTIPLE PERSPECTIVES

The students work in small groups for 15 min and come up with ideas.

RESEARCH & REVISE

This will occur throughout group and assigned projects.

TEST YOUR METTLE

Each group member builds a different molecule.

GO PUBLIC

One or more students solve the challenge on the board

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