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Lecture 9-02 - Lecture 9/02 Chapter 2 Water The solvent of...

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Lecture 9/02 Chapter 2: Water: The solvent of life Earth is unique in this solar system because of water Water sculpted Earth's surface Water apparently also sculpted Mars surface, but disappeared from the planet Water's unusual properties allowed the evolution of life Water as a solvent allows the complex interactions of biomolecules What is Water? water contains one O and 2 H atoms each linked by single covalent bonds O is more electronegative, pulls electrons from hydrogen, so that the electrons are not shared equally in the bond--polar the bond angle in water is bent at 104.5 degrees--"V" shape methane--electrons are shared more equally; nonpolar carbon dioxide--polar, but linear; attraction of electrons by oxygen is equal on both sides Hydrogen Bonding of Water most unique property--probably essential for evolution of life forms H bonds with itself and other molecules H bonds are stronger than other non-covalent bonds H bonds most specific of non-covalent interactions H bonds responsible for the thermal properties of water Hydrogen Bonds each water molecule can bond with 4 other water molecules both a H bond acceptor and donor--learning objective 1 water is actually a "net" of molecules reason for the high boiling point and heat of vaporization: energy needed to break the H bonds freezing causes the "net" to become a rigid tetrahedral lattice lattice breaks, molecules move back closer together makes liquid water denser than solid-- ice floats--allows aquatic life to survive in freezing temperatures
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Other Types of Non-Covalent Bonds -- Learning objective 2 Electrostatic or charge-charge---interactions between oppositely charged molecules (+/- type of interaction) Hydrophobic--nonpolor molecules associate with each other to get away from the water; important in protein structure van der Waals--short range interactions in a protein or nucleic acid; attraction of nuclei from one atom are attracted to electrons of another (vice versa); but if too close then repulsion occurs from electrons These types of interaction are important for macromolecular interactions, proteins, nucleic acids, etc.
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