Resonanceï¿½-ï¿½The WikiPremed MCAT Course

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Integrated Sequence	Physics	Chemistry	Organic	Biology

The Chemical Bond

Valence electrons and the octet rule

Covalent bonding

Bond Energy

Drawing a Lewis Electron Dot Diagram of a Molecule

Formal Charge

Molecular orbital theory

Orbital hybridization

Resonance

Valence shell electron pair repulsion theory

Electronegativity difference and polarity

Ionic bonding

Lattice Energy

Bonding in Metals

Web Resources

Purdue Universityï¿½-ï¿½Resonance Hybrids
Concise description of resonance.

Chem1 Virtual Textbookï¿½-ï¿½Too many structures: resonance hybrids
Presentation of resonance in the context of Lewis structures but which expands to a very readable introductory quantum mechanical explanation of resonance stability.

Special points of emphasis

Work, Energy, and Power

Electricity

The Chemical Bond

Thermochemistry

The Second Law of Thermodynamics and Heat Engines

The π orbitals of an extended sequence of sp² hybridized atoms may combine to form a π system, wherein electrons are delocalized through orbital hybridization over a large number of atoms. Such resonant forms are lower energy, i.e. more stable than non-conjugated systems.

Why is that so. A simplistic way of looking at it is to say that extended conjugation allows electron charge to spread out and decrease in potential energy, a simplistic, but useful way of looking at it.

A more complete way is to say that in addition to the decrease in electrostatic potential energy, there is also greater 'quantum multiplicity' in extended hybrid orbitals.

For both of these reasons, resonance hybridization decreases the free energy of a molecular form, making it more stable.

The WikiPremed MCAT Course is a free comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum.

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