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Chemistry of Life Part I Common Constituents and Bonds

Chemistry of Life Part I Common Constituents and Bonds. Covalent Bonds. the sharing of a pair of valence electrons by two atoms. Hydrogen atoms (2 H). LE 2-10. e-. e-. Hydrogen molecule (H 2 ). A single covalent bond, or single bond, is the sharing of one pair of valence electrons

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Chemistry of Life Part I Common Constituents and Bonds

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  1. Chemistry of Life Part I Common Constituents and Bonds

  2. Covalent Bonds • the sharing of a pair of valence electrons by two atoms

  3. Hydrogen atoms (2 H) LE 2-10 e- e- Hydrogen molecule (H2)

  4. A single covalent bond, or single bond, is the sharing of one pair of valence electrons • A double covalent bond, or double bond, is the sharing of two pairs of valence electrons • Covalent bonds can form between atoms of the same element or atoms of different elements • A molecule is two or more covalently bonded atoms Strong bond

  5. LE 2-11b Name (molecular formula) Electron- shell diagram Structural formula Space- filling model Oxygen (O2)

  6. LE 2-11c Name (molecular formula) Electron- shell diagram Structural formula Space- filling model Water (H2O)

  7. Electronegativity • an atom’s attraction for the electrons in a covalent bond Examples: Oxygen and nitrogen are highly electronegative • The more electronegative an atom, the more strongly it pulls shared electrons toward itself

  8. Nonpolar covalent bond • the atoms share the electron equally -molecule has no charge (neither positive nor negative)

  9. Molecular Oxygen LE 2-11b Name (molecular formula) Electron- shell diagram Structural formula Space- filling model Oxygen (O2) Nonpolar covalent molecule Neutral

  10. Polar covalent bond • one atom is more electronegative • the atoms do not share the electron equally • Partial negative and positive charges

  11. – O H H + + H2O H2O: Polar covalent molecule LE 2-12

  12. Ionic Bonds • Formed by the transfer of electrons from one atom to another • After transfer, both atoms charged • A charged atom (or molecule) is called an ion • Weaker than covalent bond

  13. Anion • negatively charged ion • Cation • positively charged ion • Ionic bond • attraction between an anion and a cation

  14. LE 2-13 Na Cl Na+ Cl– Sodium atom (an uncharged atom) Chlorine atom (an uncharged atom) Sodium ion (a cation) Chlorine ion (an anion) Sodium chloride (NaCl)

  15. Ionically bonded atoms • ionic compounds, or salts e.g. NaCl • often crystals

  16. LE 2-14 Na+ Cl–

  17. Hydrogen Bonds • when a hydrogen atom covalently bonded to one electronegative atom is attracted to another electronegative atom • Example: water (H2O) • Weak, but many together are strong

  18. – + LE 2-15 Water (H2O) + Hydrogen bond – Ammonia (NH3) + + +

  19. Van der Waals Interactions • Attraction between adjacent atoms by fleeting charge differences • Very weak • Collectively, can be strong, as between molecules of a gecko’s toe hairs and a wall surface

  20. Autumn K, Sitti M, Liang YA, Peattie AM, Hansen WR, Sponberg S, Kenny TW, Fearing R, Israelachvili JN, Full RJ. 2002. Evidence for van der Waals adhesion in gecko setae. Proc Natl Acad Sci USA: 99(19):12252-6. Department of Biology, Lewis & Clark College, Portland, OR 97219, USA. autumn@lclarke.edu Kellar Autumn

  21. Order of Relative Bond Strength Covalent >ionic> hydrogen> Van der Waals In biological systems, often many weak bonds collectively are strong and help stabilize structures. Example: DNA double helix: held together through H-bonds

  22. Molecular Structure of Molecules is Crucial For example Between hormone and hormone receptor

  23. Nitrogen Carbon Hydrogen Sulfur LE 2-17a Natural endorphin Oxygen Morphine Structures of endorphin and morphine

  24. LE 2-17b Natural endorphin Morphine Endorphin receptors Brain cell Binding to endorphin receptors

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