Bonding, Carbon and Water

1. Bonding, Carbon and Water Mini Lecture 2.2 AP Biology

2. Atoms with unfilled outer shells tend to undergo chemical reactions to fill their outer shells. They can attain stability by sharing electrons with other atoms (covalent bond) or by losing or gaining electrons (ionic bond) The atoms are then bonded together into molecules. Octet rule—atoms with at least two electron shells form stable molecules so they have eight electrons in their outermost shells.

4. Ionic bonds Ions are charged particle that form when an atom gains or loses one or more electrons. Cations—positively charged ions Anions—negatively charged ions Ionic bonds result from the electrical attraction between ions with opposite charges. The resulting molecules are called salts.

6. Covalent bonds Covalent bonds form when two atoms share pairs of electrons. The atoms attain stability by having full outer shells. Each atom contributes one member of the electron pair.

8. Carbon atoms have four electrons in the outer shell—they can form covalent bonds with four other atoms.

9. Strength and stability—covalent bonds are very strong; it takes a lot of energy to break them. Multiple bonds Single—sharing 1 pair of electrons Double—sharing 2 pairs of electrons Triple—sharing 3 pairs of electrons N N C H C C

10. Degree of sharing electrons is not always equal. Electronegativity—the attractive force that an atomic nucleus exerts on electrons It depends on the number of protons and the distance between the nucleus and electrons.

12. If two atoms have similar electronegativities, they share electrons equally, in what is called a nonpolar covalent bond. If atoms have different electronegativities, electrons tend to be near the most attractive atom, in what is called a polar covalent bond

14. Polar Covalent Bonds • Electronegative O pulls e- from H • This causes a partial (+) charge on the H, and a partial (-) charge on the O • Partial charges are indicated by lower case deltas (d) • The bonds between O and H are polar covalent bonds d+ d+ d-

15. Water Forms Hydrogen Bonds • Partial charges interact • Hs attracted to Os • Causes water to self-associate

16. Hydrogen Bonding • Gaseous water molecules interact very little • Liquid water molecules are hydrogen bonded, but can slip past each other • As water freezes, it forms a crystalline lattice because H bonding lasts longer

17. Water is “Sticky” • Water is sticky because of H bonding • Cohesive – sticks to itself • Adhesive – sticks to other things • Meniscus

18. Water has High Surface Tension • Water sticks to itself strongly and so has high surface tension • Forms meniscus • Forms droplets • Small animals can ‘skate’ on surface

19. Other water properties • High specific heat • High heat of vaporization • Great solvent

20. Carbon • Carbon: • Is the single most abundant element of Life • Is neither strongly electronegative nor positive • Can share 4 electrons and form 4 covalent bonds with 4 other atoms (single, double or triple bonds) • Interacts with many other atoms • Makes a great variety of molecules – because it can form straight or branched chains or rings • The diversity of carbon-carbon interactions provides for the diversity of biomolecules: lipid, carbohydrate, protein, nucleic acid

21. Carbon Double Bonds • 2 double bonds connect O to C on either side, and the molecule is linear. • As a result, oxygen atoms pull on electrons in a linear manner and so carbon dioxide is nonpolar.

22. H H C C H H C C H H H H C C H H C C C C Covalent Carbon-Carbon Bonds • Carbon may form… • single bonds • ethane • double bonds • ethene • triple bonds • ethyne H H H H H H H H H H H C C H H H

23. Hydrocarbons: C & H

24. R = radical & can Represent Any Atom or atoms

26. Macromolecules Most biological molecules are polymers (poly, “many”; mer, “unit”), made by covalent bonding of smaller molecules called monomers.

27. 4 MAIN Macromolecules • Proteins: Formed from different combinations of 20 amino acids • Carbohydrates—formed by linking similar sugar monomers (monosaccharides) to form polysaccharides • Nucleic acids—formed from four kinds of nucleotidemonomers • Lipids—noncovalent forces maintain the interactions between the fatty acid monomers

28. Polymers are formed and broken apart in reactions involving water. Condensation—removal of water puts monomers together (dehydration synthesis) Hydrolysis—addition of water breaks a polymer into monomers

31. PDQ 2.2

32. 1. Ionic vs. Covalent Ionic Covalent Both atoms share electrons in order to fill their outer shells Occurs between 2 nonmetals Bond can be polar (shared unequally)or nonpolar (shared equally) • 1 atom donates to another atom in order to fill their outer shells • Metal donates to the nonmetal • Bond occurs from attraction of cation (+) to anion (-)

33. 2. Electronegativity • Attractive force than an atomic nucleus exerts on electrons in a covalent bond • Causes covalent bonds to not be shared equally • Causes partial charges on atoms

34. 3. Nonpolar Covalent vs. Polar Covalent Nonpolar Covalent Polar Covalent Bond in which electrons are not shared equally Occurs when 2 atoms are NOT close to each other in electronegativity Causes partial charges on atoms • Bond in which electrons are shared equally • Occurs when 2 atoms are close to each other in electronegativity

35. 4. Hydrogen bond and differences • Occurs between a partially positive charged atom and a partially negatively charged atom • It differs from a covalent bond because electrons are not being shared • It differs from an ionic bond because the charges are partial • It is weaker than both a covalent and an ionic bond

36. 5. Hydrophilic vs. Hydrophobic Hydrophilic Hydrophobic Water fearing Nonpolar Attracted to nonpolar substances like oil Does not dissolve in water • Water loving • Polar • Attracted to water • Dissolves in water • Usually caused by polarity

37. 6. Van Der Waals Compare Contrast Very weak compared to all other chemical bonds Interaction of electrons of nonpolar substances only  no polar substances are involved • Chemical bond

38. 7. Rank bonds from least to greatest energy • Van Der Waals • Hydrophobic interactions • Hydrogen Bond • Ionic Bond • Covalent Bond

39. 8. Why is water polar? • Because the oxygen and hydrogen do NOT share their electrons equally • Oxygen wants the electron more because it is MORE electronegative • Therefore Oxygen gets more of a negative charge and hydrogen gets more of a positive charge • This means it is polar and unbalanced.

40. 9. Water bonding – showing hydrogen bond

41. 10. Water properties

42. 11. Inorganic vs. Organic Inorganic Organic Has carbon AND hydrogen LARGE • No carbon AND hydrogen • smaller

43. 12. Carbon  • Has 4 Valence electrons • Can bond with 4 other atoms • Possibilities are endless of what carbon can make!

44. 13. Functional Groups

45. 14. Bonding interactions for each functional group

46. 15. Macromolecules • Carbohydrates • Lipids • Proteins • Nucleic Acids

47. 16. Making Macromolecules • Condensation or Dehydration Synthesis

48. 16. Breaking Macromolecules • Hydrolysis