Bonding, Carbon and Water Mini Lecture 2.2 AP Biology

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.

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.

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.

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

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 C H C C N N

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.

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

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- Biology, Sixth Edition Chapter 2, Atoms and Molecules

Water Forms Hydrogen Bonds Partial charges interact Hs attracted to Os Causes water to self-associate Biology, Sixth Edition Chapter 2, Atoms and Molecules

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 Biology, Sixth Edition Chapter 2, Atoms and Molecules

Water is “Sticky” Meniscus Water is sticky because of H bonding Cohesive – sticks to itself Adhesive – sticks to other things Meniscus Biology, Sixth Edition Chapter 2, Atoms and Molecules

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 Biology, Sixth Edition Chapter 2, Atoms and Molecules

Other water properties High specific heat High heat of vaporization Great solvent

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 Biology, Sixth Edition Chapter 3, Chemistry of Life: Organic Compounds

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. Biology, Sixth Edition Chapter 3, Chemistry of Life: Organic Compounds

Covalent Carbon-Carbon Bonds Carbon may form… single bonds ethane double bonds ethene triple bonds ethyne H H C H C H H H H C H H H C H H H C C H H C H Biology, Sixth Edition Chapter 3, Chemistry of Life: Organic Compounds

Hydrocarbons: C & H Biology, Sixth Edition Chapter 3, Chemistry of Life: Organic Compounds

R = radical & can Represent Any Atom or atoms

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

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 nucleotide monomers Lipids—noncovalent forces maintain the interactions between the fatty acid monomers

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 ANIMATED TUTORIAL 2.2 Macromolecules: Carbohydrates and Lipids

PDQ 2.2

1. Ionic vs. Covalent Ionic Covalent 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 (-) 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)

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

3. Nonpolar Covalent vs. Polar Covalent Bond in which electrons are shared equally Occurs when 2 atoms are close to each other in electronegativity 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

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

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

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

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

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.

9. Water bonding – showing hydrogen bond

10. Water properties Property Definition Special Example High heat capacity Water is slow to change temperature Many hydrogen bonds Takes a long time to boil water High heat of vaporization Lots of energy is needed to go from liquid to gas Hydrogen bonds have to be broken Sweating Evaporative Cooling When water evaporates it cools Breaking hydrogen bonds When you sweat, you cool down Cohesion Attraction to each other Polarity in hydrogen bonds Puddles Adhesion Attraction to other molecules capillarity Surface Tension Attractive intermolecular forces at the surface of a liquid Insects walking on water

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

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

13. Functional Groups Functional Group Drawing Name of Compounds Example Property Hydroxyl Alcohols Ethanol Polar. Hydrophilic Carbonyl 1 Aldehydes Acetalaldehyde Very reactive Carbonyl 2 Ketones Acetone Important in Carbohydrates Carboxyl Carboxylic Acids Acetate Acidic. Ionizes in living tissues Amino Amines Methylamine Basic. Accepts H+’s in living tissues Sulfhydryl Thiols Mercaptoethanol Can form disulfide bridges Phosphate Organic Phosphates 3-Phosphoglycerate Negative charged.

14. Bonding interactions for each functional group Hydroxyl Condensation Carbonyl 1 – Aldehyde Energy Releasing, Condensation Carbonyl 2 - Ketone Energy reactions Carboxyl Condensation – gives up OH; Energy releasing Amino Condensation – gives up H Sulfhydryl Forms disulfide brides in proteins Phosphate Condensation – gives up OH, hydrolysis when bonded to another phosphate

15. Macromolecules Carbohydrates Lipids Proteins Nucleic Acids

16. Making Macromolecules Condensation or Dehydration Synthesis

16. Breaking Macromolecules Hydrolysis