• What types of bonds are identified in the followingillustration of a water molecule interacting with an ammoniamolecule? *– A: Bonds 1 are polar covalent bonds, bond 2is a hydrogen bond, and bonds 3 arenonpolar covalent bonds.– B: Bonds 1 and 3 are polar covalent bondsand bond 2 is a hydrogen bond.– C: Bonds 1 and 3 are polar covalent bondsand bond 2 is an ionic bond.– D: Bonds 1 and 3 are nonpolar covalentbonds and bond 2 is a hydrogen bond.– E: Bonds 1 and 3 are polar covalent bondsand bond 2 is a nonpolar covalent bond.• Which drawing depicts the electron configuration ofneon (2010Ne)?– A– B– C– D– ELE 3-2HydrogenbondsFour emergent properties of watercontribute to Earth’s fitness for life• Four of water’s properties that facilitate anenvironment for life:Cohesive behaviorAbility to moderate temperatureExpansion upon freezingVersatility as a solventCohesion• Collectively, hydrogen bonds hold watermolecules together, a phenomenon calledcohesion• Cohesion helps the transport of water againstgravity in plants• Adhesion of water to plant cell walls also helpsto counter gravityLE 3-3Water-conducting cells100 µm• Surface tension is a measure of how hard it isto break the surface of a liquid• Surface tension is related to cohesionModeration of Temperature• Water absorbs heat from warmer air andreleases stored heat to cooler air• Water can absorb or release a largeamount of heat with only a slight change inits own temperatureHeat and Temperature• Kinetic energy is the energy of motion• Heat is a measure of the total amount of kinetic energydue to molecular motion• Temperature measures the intensity of heat due to theaverage kinetic energy of moleculesWater’s High Specific Heat• The specific heat of a substance is the amountof heat that must be absorbed or lost for 1gram of that substance to change itstemperature by 1ºC• Water’s high specific heat minimizestemperature fluctuations to within limits thatpermit life– Heat is absorbed when hydrogen bonds break– Heat is released when hydrogen bonds formEvaporative Cooling• Evaporation is transformation of a substance fromliquid to gas• Heat of vaporization is the heat a liquid must absorbfor 1 gram to be converted to gas• As a liquid evaporates, its remaining surface cools, aprocess called evaporative cooling• Evaporative cooling of water helps stabilizetemperatures in organisms and bodies of waterInsulation of Bodies of Waterby Floating Ice• Ice floats in liquid water because hydrogen bonds in iceare more “ordered,” making ice less dense• If ice sank, all bodies of water would eventually freezesolid, making life impossible on EarthThe Solvent of Life• A solution is a liquid that is a homogeneous mixture ofsubstances• A solvent is the dissolving agent of a solution• The solute is the substance that is dissolved• Water is a versatile solvent due to its polarity• An aqueous solution is one in which water is thesolvent• Water is an effective solvent because itreadily forms hydrogen bonds• When an ionic compound is dissolved inwater, each ion is surrounded by a sphereof water molecules, a hydration shellLE 3-6Na+Na+Cl–Cl–++++++++–––––––––––• Water can also dissolve compounds madeof nonionic polar molecules• Even large polar molecules such asproteins can dissolve in water if they haveionic and polar regionsLE 3-7a Lysozyme moleculein a nonaqueous environment.LE 3-7bLysozyme molecule in a aqueous environment.Hydrophilic and HydrophobicSubstances• A hydrophilic substance is one that has anaffinity for water• A hydrophobic substance is one that does nothave an affinity for waterSolute Concentration inAqueous Solutions• Most biochemical reactions occur in water• Chemical reactions depend on collisions ofmolecules and therefore on theconcentration of solutes in an aqueoussolution• Molecular mass is the sum of all masses of allatoms in a molecule• Numbers of molecules are usually measured inmoles, with one mole being 6.02 x 1023molecules• Molarity is the number of moles of solute perliter of solutionDissociation of water moleculesleads to acidic and basic conditions• A hydrogen atom in a hydrogen bond betweentwo water molecules can shift from one to theother:– The hydrogen atom leaves its electron behindand is transferred as a proton, or hydrogen ion(H+)– The molecule with the extra proton is now ahydronium ion (H3O+)– The molecule that lost the proton is now ahydroxide ion (OH-)LE 3-UN53Hydroniumion (H3O+)Hydroxideion (OH–)• The process can be described in a simplifiedway as the separation of a water molecule intoa hydrogen ion (H+) and a hydroxide ion (OH-)• Though statistically rare, the dissociation ofwater molecules has a great effect onorganisms• Changes in concentrations of H+ and OH- candrastically affect the chemistry of a cellEffects of changes in pH• Concentrations of H+ and OH- are equal in purewater• Adding certain solutes, called acids and bases,modifies the concentrations of H+ and OH-• Biologists use the pH scale to describe howacidic or basic (the opposite of acidic) asolution isAcids and Bases• An acid is any substance that increasesthe H+ concentration of a solution• A base is any substance that reduces theH+ concentration of a solutionThe pH Scale• The pH of a solution is determined by therelative concentration of hydrogen ions• Acidic solutions have pH values less than 7• Basic solutions have pH values greater than 7• Most biological fluids have pH values in therange of 6 to 8LE 3-8pH Scale01234567891011121314Oven cleanerHousehold bleachHousehold ammoniaMilk of magnesiaSeawaterPure waterHuman bloodUrineRainwaterBlack coffeeTomato juiceVinegar, beer, wine,colaDigestive (stomach)juice, lemon juiceBattery acidNeutral[H+] = [OH–]Increasingly Acidic[H+] > [OH–]Increasingly Basic[H+] < [OH–]Buffers• The internal pH of most living cells must remainclose to pH 7• Buffers are substances that minimize changesin concentrations of H+ and OH- in a solution• Most buffers consist of an acid-base pair thatreversibly combines with H+LE 4-3MolecularFormulaStructuralFormulaBall-and-StickModelSpace-FillingModelMethaneEthaneEthene (ethylene)• The electron configuration of carbon gives itcovalent compatibility with many differentelements• The valences of carbon and its most frequentpartners (hydrogen, oxygen, and nitrogen) arethe “building code” that