5.5C: $$CH_4$$

This module seeks to explain the bonding of the 4 Hydrogen atoms to the 1 Carbon atom in the molecule CH4 (methane),using the molecular orbital theory. Molecular orbital theory describes orbitals that are formed with the interaction of the atomic orbitals of given atoms. These orbitals are spread out over the entire molecule and electrons fill these orbitals in accordance with the aufbau principle.

Introduction

Various concepts explain the molecular orbital theory in the bonding in methane, including character tables, symmetry, LGOs (ligand group orbital approach), and a qualitative MO diagram.

The Symmetry of CH4

• CH4 belongs to the Td point group and contains: 8C3 axes, 3C2 axes, 6S4 axes, and a dihedral plane of symmetry. Using the character table for the Td point group,

Character Table for Td Point group

 Td E 8C3 3C2 6S4 6sigmad A1 1 1 1 1 1 A2 1 1 1 -1 -1 E 2 -1 2 0 0 T1 3 0 -1 1 -1 T2 3 0 -1 -1 1

Molecular Orbital Diagram for CH4

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References

1. Housecroft, C; Sharpe, A. (2008). Bonding in Polyatomic Molecules. In: Pearson Education Limited Inorganic Chemistry. Edinburgh Gate: Pearson Education Limited. pgs. 33, 130-131.

• This is not meant for references used for constructing the module, but as secondary and unvetted information available at other site
• Link to outside sources. Wikipedia entries should probably be referenced here.

Problems

What are ligand group orbitals, and how are they used in MO theory in polyatomic molecules?

How many Vibrational modes and IR/Ramen stretches are there in CH4?

What are the major differences between VB theory and MO theory applied to polyatomic molecules?

Contributors

• Name #1 here (if anonymous, you can avoid this) with university affiliation