2.5 Chapter 2 Summary
Christelle Sabatier
Learning Objectives
- Predict the water solubility of small molecules based on their structures.
- Identify carbons and hydrogens in small molecule structures.
2.1 Atoms, Ions, and Molecules (a little chemistry review)
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Atoms are composed of protons, neutrons, and electrons. The number of protons defines the element; electrons in the outer shell determine chemical behavior.
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Isotopes have varying neutron numbers but similar chemical properties.
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Ions form when atoms gain or lose electrons, becoming charged (cations: positive; anions: negative).
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Molecules are two or more atoms held together by chemical bonds. Biological molecules include water, salts, organic compounds, and so on.
2.2 Covalent Bonds and Other Molecular Interactions
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Covalent bonds involve sharing electron pairs:
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Nonpolar covalent: equal sharing (e.g., O₂, CH₄)
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Polar covalent: unequal sharing due to electronegativity differences (e.g., H2O)
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Electronegativity determines bond polarity; greater differences lead toward ionic character.
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Ionic bonds form when electrons transfer fully, creating oppositely charged ions.
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Non-covalent interactions:
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Hydrogen bonds are weak attractions between atoms with a partial positive charge and atoms with a partial negative charge; they are crucial for water’s properties, protein folding, and DNA stability.
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Van der Waals forces are transient attractions due to temporary dipoles between atoms forming nonpolar covalent bonds.
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These weaker forces significantly contribute to macromolecular structure and function.
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2.3 Water
- Polarity and hydrogen bonding: H2O’s bent shape and polar bonds create dipoles, enabling extensive hydrogen bonding between molecules.
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Unique properties:
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Water’s properties include high melting/boiling points, surface tension, heat capacity, and cohesion due to H-bonds.
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Ice forms an open, hydrogen-bonded lattice, making it less dense than liquid water.
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Biological roles:
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Water is a universal solvent that dissolves hydrophilic molecules and impacts biochemical interactions.
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Thermal stability supports enzyme function and climate buffering.
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Dynamic network: Bonds continually form and break in picoseconds, yet they collectively shape water’s macroscopic behavior.
2.4 Carbon
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Fundamental to life: Carbon’s four valence electrons allow up to four covalent bonds, enabling diverse structures.
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Hydrocarbons: Chains or rings of C and H (e.g., methane, propane) store significant energy and serve as fuel.
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Bond variety: Single, double, and triple C–C bonds influence molecular geometry and reactivity.
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Isomers: Molecules with the same formula but different structure are called isomers and lead to varied properties (structural, cis-trans).
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Enantiomers: Mirror-image molecules that are not superimposable (e.g., L- and D-amino acids) are called enantiomers; often only one form (usually L) is biologically active.
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Functional groups: Common reactive attachments on carbon backbones include hydroxyl, methyl, carbonyl, carboxyl, amino, phosphate, and sulfhydryl. They confer specific chemical traits—hydrophilic, hydrophobic, acidic, and basic—and mediate macromolecule activity and interactions.
How These Chapters Interconnect:
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From atoms → life: Building blocks (atoms and ions) form molecules via bonds; carbon chemistry provides the backbone of diverse biological macromolecules.
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Interactions shape biology: Non-covalent forces (H‑bonds, van der Waals) and water’s polarity determine structure, function, and interactions in cells.
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Functional diversity: Carbon’s bonding versatility and functional groups enable the complexity of proteins, nucleic acids, lipids, and carbohydrates.
Practice Questions
Licenses and Attributions
“2.5 Chapter 2 Summary” was initially generated by ChatGPT4.0 and then modified by Christelle Sabatier. “2.5 Chapter 2 Summary” is licensed under CC-BY-NC 4.0.