Session Overview
| Modules | Bonding and Molecules |
| Concepts | linear combination of atomic orbitals–molecular orbitals (LCAO-MO): energy level diagrams, bonding and anti-bonding orbitals, and hybridization, paramagnetism and diamagnetism |
| Keywords | Wolfgang Pauli, primary bond, ionic bond, covalent bond, metallic bond, electronegativity, metal, non-metal, superposition, alkali metal, node, lobe, nodal plane, electron density, alloy, electronic conductivity, ionic conductivity, molten salt, liquid metal, energy level diagram, atomic orbital, molecular orbital, bonding orbital, antibonding orbital, paramagnetism, sigma bond, pi bond, hybridization, single bond, double bond, triple bond, diamagnetism, octet stability, polar bond, polar molecule, nonpolar molecule, homonuclear molecule, heteronuclear molecule, Schrödinger's equation, linear superposition, atomic orbital wavefunction, conservation of orbital states, Aufbau principle, quantum numbers, Pauli exclusion principle, Hund's rule, bonding electron, nonbonding electron, unpaired electrons, Lewis structure, electron transfer |
| Chemical Substances | ethylene (C2H4), methane (CH4), carbon (C), acetylene (C2H2), titanium tetrachloride (TiCl4), sulfur hexafluoride (SF6), bromine pentafluoride (BrF5), iodine tetrafluoride (IF4-), helium (He), dilithium (Li2), disodium (Na2), nitrogen (N2), oxygen (O2), fluorine (F2) |
| Applications | sodium vapor lamps |
Prerequisites
Before starting this session, you should be familiar with:
Looking Ahead
Prof. Sadoway discusses the shapes of molecules (Session 11).
Learning Objectives
After completing this session, you should be able to:
- Define polar bond, polar molecule, dipole moment.
- Identify three types of primary bonds: ionic, covalent, metallic.
- Explain why homonuclear molecules and molecules containing symmetric arrangements of identical polar bonds must be nonpolar.
- Sketch energy level diagrams for molecules using LCAO-MO, and identify the bonding orbitals and antibonding orbitals.
- Explain how paramagnetism occurs.
- Describe the components of sigma bonds and pi bonds.
- Explain the source of electronic conductivity and ionic conductivity.
Reading
Archived Lecture Notes #2 (PDF), Section 3
| Book Chapters | Topics |
|---|---|
| [Saylor] 9.2, "Localized Bonding and Hybrid Atomic Orbitals." | Valence bond theory: a localized bonding approach; hybridization of s and p orbitals; hybridization using d orbitals |
| [Saylor] 9.3, "Delocalized Bonding and Molecular Orbitals." | Molecular orbital theory: a delocalized bonding approach; bond order in molecular orbital theory; molecular orbitals formed from ns and np atomic orbitals; molecular orbital diagrams for second-period homonuclear diatomic molecules; molecular orbitals in heteronuclear diatomic molecules |
| [Saylor] 9.4, "Combining the Valence Bond and Molecular Orbital Approaches." | Multiple bonds; molecular orbitals and resonance structures |
Lecture Video
> Download from iTunes U (MP4 - 216MB)
> Download from Internet Archive (MP4 - 216MB)
Resources
Lecture Summary
Prof. Sadoway discusses the following concepts:
- Linear combination of atomic orbitals – molecular orbitals (LCAO-MO)
- Orbitals split into bonding orbitals (lower) and antibonding orbitals (higher). Electrons fill from lowest energy up.
- Types of bonds:
- sigma = no nodal plane separates nuclei
- pi = a nodal plane separates nuclei
-
Paramagnetism: from unpaired electrons in molecular orbitals
- e.g. liquid oxygen is paramagnetic – can be held by a magnetic field
Homework
Textbook Problems
| [Saylor] Sections | Conceptual | Numerical |
|---|---|---|
| [Saylor] 9.2, "Localized Bonding and Hybrid Atomic Orbitals." | none | 1, 2, 7, 8 |
| [Saylor] 9.3, "Delocalized Bonding and Molecular Orbitals." | none | 1, 2, 6, 7, 11, 13, 14, 18 |
For Further Study
People
Wolfgang Pauli - 1945 Nobel Prize in Physics
Other OCW and OER Content
| Content | Provider | Level | Notes |
|---|---|---|---|
| 5.111 Principles of Chemical Science | MIT OpenCourseWare | Undergraduate (first-year) |