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Atoms, Molecules, and LifeThe Importance of WaterChapter 2Atoms The basic structural unit of matter.protonneutronelectronnucleuselectron shellHydrogenHeliumCarbon21 341HHydrogen1.0081 - Atomic Number = # of protons2 - Element3 - Symbol4 - Molecular Mass ~ # protons + # neutrons6 CCarbon12.0121 34Properties of Elements Element: a substance that cannot be brokendown nor converted to another substanceby ordinary chemical means. Isotope: atoms of an element that containdifferent numbers of neutrons 12C has 6 protons and 6 neutrons (normal) 14C has 6 protons and 8 neutrons (heavy carbon) Some isotopes are radioactive, they spontaneously break apart, releasing energy and forming new elements.Electrons: the key to bonding Negatively charged Repel each other Attracted to the positively-charged nucleus Can become excitedExcited Electrons:Disobeying Electron Shells Electrons orbit through different energy levels 1st shell: up to 2 electrons (e-) 2nd shell (and each larger shell): up to 8 e- Always fill up the lowest energy level first More stable when shells are fullFree Radicals Atoms with one or more unpaired electron intheir outer shell. Very unstable. Capture electrons from neighboringmolecules, creating new free radicals. Can lead to cell death and a variety ofdiseases. Antioxidants react with free radicals, rendering them harmless to the body.Interacting Elements An atom whose outer electron shell is fullcannot interact with other atoms and is calledinert. Atoms is reactive when its outer electron shellis only partially full and it can react with otheratoms.Molecules Two or more atoms of the same or differentelements held together. Molecules formed from different elementsare compounds. Atoms can form three main types of bonds: Ionic, Covalent, and Hydrogen bondsIonic Bonds An electron is transferred, creatingpositive and negative ions that attractone another.Sodium (11 p+, 11 n) Chlorine (17 p+, 18 n)Example: MgCl2 MgCl2: Total # protons: 12 + (17)*2 = 46 Total # electrons: 12 + (17)*2 = 46 Combined MolecularMass: 24.31 + (34.45)*2 = 93.21 g/mol12MgMagnesium24.3117ClChlorine34.45Chlorine: 17 protons 18 neutrons 17 electrons (7 e- in the outer shell)Magnesium: 12 protons 12 neutrons 12 electrons (2 e- in the outer shell)Ionic bonding, with one electron from Magnesiumdonated to each Chlorine atomCovalent Bonds Electron pairs are shared. Nonpolar covalent bonds: equal sharing. Two hydrogen atoms share electrons to form uncharged H2. Electrons spend the same amount of timearound each nuclei.Covalent Bonds, continued Polar covalent bonds: unequal sharing. Electrons spend more time around one atomthan the other.- -++Oxygen is slightly negativeHydrogen is slightly positiveWater, H2OExample: NH3,Ammonia Polar, covalent bonding, sharingthe electrons of Hydrogen to fillNitrogens outer e- shell. NH3: Total # protons: 7 + (1)*3 = 10 Total # electrons: 7 + (1)*3 = 10 Combined MolecularMass: 14.01 + (1.008)*3 = 17.034 g/mol7NNitrogen14.01Hydrogen: 1 proton 0 neutrons 1 electrons (1 e- in the outer shell)Nitrogen: 7 protons 7 neutrons 7 electrons (5 e- in the outer shell)1HHydrogen1.008Covalent bonds are the most common bondfound in biologic systems.Hydrogen Bonds The slightly attraction between atomsinvolved in polar covalent bonds fromdifferent molecules.- -++- -++- -++Properties of Water Life likely began underwater. All living organisms contain 60-90% H2O. All life depends on water. (examples: Photosynthesis and Digestion)Properties of Water1. Very good solvent. It is able to dissolve a wide range ofsubstances.Solvent: WaterSolute: SaltSolution:Salt WaterProperties of Water Because of itspolarity, waterattracts bothpositive andnegative ions,breaking ionicbonds.Properties of Water2. Hydrophobic and Hydrophilic qualities. Hydrophobic (water-fearing)molecules are non-polar anduncharged.Water cannot dissolve them.Lipids, Fats and OilsHydrophilic (water-loving)molecules are polar.Water dissolves the covalent bonds.Sugars, Salts, and Amino AcidsProperties of Water3. Water molecules tend to stick together. Because of their hydrogen bonds, watermolecules have high cohesion(stickiness). Cohesion of water molecules at thesurface creates surface tension. The tendency for the water surface to resistbreaking.Examples of SurfaceTension and CohesionProperties of Water4. Water can be acidic, basic, or neutral. Water molecules are easily ionized: Pure water has equal concentrations ofhydroxide (OH-) and hydrogen (H+) ions.Acids Acidic solutions have a higher concentration of H+than OH-. Acids release hydrogen ions when dissolved inwater. Many acidic solutions taste sour (vinegar, lemonjuice, etc).Bases Basic solutions have a higher concentration of OH-. Bases combine with hydrogen ions, reducing theirnumber. Many basic solutions taste bitter, and are veryharmful if consumed (ammonia, bleach, etc).pH Scale (0-14) Measures the ratio of H+ to OH-. Neutrality (equal concentrationsof H+ and OH-) is set to 7. Acids have a pH below 7. Bases have a pH above 7.NeutralBasicAcidic1407Buffers A complex molecule that helps maintain asolution at a constant pH. Can combine with H+ to increase pH. Releases H+ to combine with OH- when needed to decrease pH.Example: Carbonate Buffering of BloodCO32- HCO3- H2CO3 pH ~ 6 pH ~ 9.5Properties of Water H20 heats slowly Takes a lot of energy to break H-bonds H20 moderates high and low temperatures H20 freezes slowly A large amount of energy must be removed toform ice crystalsWater moderates the effects oftemperature changes.Water forms an unusual solid:Water forms an unusual solid:IceIce Less dense than liquid water!Less dense than liquid water!LiquidLiquid SolidSolidHomeworkChapter 2The lizard in the beginning of this lectureappears to be running on water.Aside from the speed at which the lizard runs,what properties of water allow the lizard tomove like this? How does this property work?(i.e. describe the arrangement of molecules that giveswater this property)Give two other examples where these propertiesof water are used in nature.