Linus Pauling was one of the most influential chemists of the twentieth century because he helped explain why atoms join in specific ways to form molecules. His work connected quantum mechanics, laboratory chemistry, and clear visual models of bonds. By making ideas like hybrid orbitals, resonance, and electronegativity easier to use, he gave chemists tools for predicting molecular structure and reactivity.
His book The Nature of the Chemical Bond shaped how generations of students learned chemistry.
Key Facts
- Pauling received the 1954 Nobel Prize in Chemistry for research on the nature of the chemical bond.
- Pauling received the 1962 Nobel Peace Prize for his public work against nuclear weapons testing.
- Electronegativity difference helps estimate bond type: larger difference usually means more ionic character.
- Percent ionic character can be estimated by % ionic = [1 - e^(-0.25(Δχ)^2)] x 100.
- Pauling helped describe resonance, where one Lewis structure is not enough to represent the real electron distribution.
- Pauling and coworkers proposed the alpha helix as a major protein secondary structure stabilized by hydrogen bonds.
Vocabulary
- Chemical bond
- A chemical bond is an attractive interaction that holds atoms together in a molecule or crystal.
- Electronegativity
- Electronegativity is a measure of how strongly an atom attracts shared electrons in a chemical bond.
- Resonance
- Resonance is a model in which multiple Lewis structures are used to describe one real molecule with delocalized electrons.
- Hybrid orbital
- A hybrid orbital is a mixed atomic orbital used to explain molecular shapes and bonding patterns such as tetrahedral carbon.
- Alpha helix
- An alpha helix is a coiled protein structure stabilized by hydrogen bonds along the protein backbone.
Common Mistakes to Avoid
- Treating electronegativity as a fixed force is wrong because it is a relative scale used to compare how atoms attract shared electrons.
- Calling every polar bond ionic is wrong because bond type is usually a continuum, and many bonds have both covalent and ionic character.
- Drawing only one resonance structure as the molecule is wrong because the real molecule is a resonance hybrid with delocalized electrons.
- Thinking the alpha helix is held together by bonds between side chains is wrong because its main stabilizing pattern is hydrogen bonding between backbone groups.
Practice Questions
- 1 Using electronegativities H = 2.20 and Cl = 3.16, calculate Δχ for HCl and decide whether the bond is nonpolar covalent, polar covalent, or mostly ionic.
- 2 Use % ionic = [1 - e^(-0.25(Δχ)^2)] x 100 to estimate the percent ionic character of a bond with Δχ = 1.8. Round to the nearest percent.
- 3 A student draws ozone, O3, with one single bond and one double bond and says one oxygen oxygen bond is permanently shorter than the other. Explain why resonance makes this conclusion incorrect.