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1、ChemistryAP BiologyChemical BondsElectronegativities of Common ElementsHydrogen2.1Oxygen3.5Carbon2.5Nitrogen3.0Sulfur2.5Phosphorus2.1Sodium0.9Chlorine3.0 Electronegativity = how well an atom “holds its electronsBonds within a moleculeBonding between atoms can be organized on a continuum between cova
2、lent and ionic bondsNonpolar CovalentPolar CovalentIonicBonds within a moleculeNonpolar covalent bond = electrons are shared evenly between bondsPolar covalent bond = electrons are shared but are more tightly held by one atomIonic bond = Electrons are not shared due to strong electronegativity diffe
3、rences (one atom “grabs the electrons from the other)Bond Type By ElectronegativityElectronegativity differenceBond Type 1.7IonicHydrogen BondsThis is a type of bond BETWEEN molecules (different from polar covalent bond)Involves the hydrogen of one molecule being attracted to a strongly electronegat
4、ive atom in another moleculeHHOHNd d-d d+d d+d d+d d-Hydrogen bonds are extremely important in biological systems. Well see them again and again:ProteinsDNAEnzymesAnd more!Img taken without permission from: :/ Van der Waals InteractionsWeak attractions when two molecules are very close togetherTempo
5、rary dipole moments in an atom can cause these tiny attractions Images taken without permission from: :/news.bbc.co.uk/1/hi/sci/tech/781611.stm Properties of WaterPolar molecule forms hydrogen bonds Hydrogen bonds give water some special characteristics:High specific heatEvaporative coolingInsulatio
6、n of bodies of waterProperties of water (cont.)High Specific HeatTakes a lot of energy to heat up 1 degreeMakes water very stableEvaporative coolingWater has a high heat of vaporizationEvaporative cooling prevents overheatingProperties of water (cont.)Insulation of bodies of waterSolid water is less
7、 dense than liquid water ice floats!Ice on top creates a “cover that keeps water below from freezing Allows fish and plants underneath to continue to exist.BuffersMaintain the pH in a solutionTypically consist of an H+ acceptor and an H+ donorWhy might this be important in living things?Image taken
8、without permission from: :/ chemistry.wustl.edu/edudev/LabTutorials/Buffer/images/Eqn10.jpg Carbon- a versatile elementEach carbon atom can form 4 bondsMolecular drawingsIn some molecular drawings, C and H are left out as a shortcutJunction between lines = CLine that ends with nothing at the end = C
9、Since C makes 4 bonds, unless otherwise noted H is assumed to be there2 ways to draw the same molecule!Functional GroupsFunctional groups are groups of atomsparticipate in many chemical reactionsHelp determine the properties of organic moleculesAlcohol (hydroxyl)Other forms: HOAldehydeOther forms: -
10、COHProperties: Polar, Soluble in waterKetoneOther forms:Properties: Polar, Soluble in water Functional groupsCH2COCH2Functional groupsCarboxylOther forms: -COOH, -COO-Properties: Acidic, Polar, Water SolubleAminoOther forms: -NH2, - NH3+Properties: Basic, PolarFunctional groupsThiolOther forms: -SHProperties: Polar, forms disulfide bridges/bonds in proteinsPhosphateOther forms: -PO42-Properties: Charged, Polar
