Y khoa, y dược - Chapter 2: Chemistry comes alive

Chapter 2 Part A Chemistry Comes AliveAnything that has mass and occupies spaceStates of matter:Solid—definite shape and volumeLiquid—definite volume, changeable shapeGas—changeable shape and volumeMatterCapacity to do work or put matter into motionTypes of energy:Kinetic—energy in actionPotential—stored (inactive) energyEnergyPLAYAnimation: Energy ConceptsChemical energy—stored in bonds of chemical substances Electrical energy—results from movement of charged particlesMechanical energy—directly involved in moving matterRadiant or electromagnetic energy—exhibits wavelike properties (i.e., visible light, ultraviolet light, and X-rays)Forms of EnergyEnergy can neither be created nor destroyed (1st law of thermodynamics)Energy may be converted from one form to anotherConversion is inefficient because some energy is “lost” as heatEnergy Form ConversionsElementsCannot be broken down by ordinary chemical means Each has unique properties:Physical propertiesAre detectable with our senses, or are measurableChemical propertiesHow atoms interact (bond) with one anotherComposition of MatterAtomsUnique building blocks for each elementAtomic symbol: one- or two-letter chemical shorthand for each elementEg: Copper Cu Sulfur S Iron Fe Potassium K Mercury Hg Phosphorus P Gold Au Iodine IComposition of MatterOxygen (O) Carbon (C) Hydrogen (H) Nitrogen (N)Major Elements of the Human BodyAbout 96% of body mass About 3.9% of body mass:calcium (Ca), phosphorus (P), potassium (K), sulfur (S), sodium (Na), chlorine (Cl), magnesium (Mg), iodine (I), and iron (Fe)Lesser Elements of the Human Body< 0.01% of body mass:Part of enzymes, e.g., chromium (Cr), manganese (Mn), and zinc (Zn)Trace Elements of the Human BodyDetermined by numbers of subatomic particlesNucleus consists of neutrons and protonsAtomic StructureNeutronsNo chargeMass = 1 atomic mass unit (amu)ProtonsPositive chargeMass = 1 amuAtomic StructureElectronsOrbit nucleusEqual in number to protons in atomNegative charge 1/2000 the mass of a proton (0 amu) Not considered in the calculation of atomic weightAtomic StructurePlanetary model Depicts fixed circular electron pathsUseful for illustrations (as in the text)Model of the AtomFigure 2.1(a) Planetary model(b) Orbital modelHelium atom2 protons (p+)2 neutrons (n0)2 electrons (e–)Helium atom2 protons (p+)2 neutrons (n0)2 electrons (e–)NucleusNucleusProtonNeutronElectroncloudElectronAtoms of different elements contain different numbers of subatomic particlesCompare hydrogen, helium and lithium (next slide)Identifying ElementsFigure 2.2ProtonNeutronElectronHelium (He)(2p+; 2n0; 2e–)Lithium (Li)(3p+; 4n0; 3e–)Hydrogen (H)(1p+; 0n0; 1e–)Atomic number = number of protons in nucleusIdentifying ElementsAtomic weight = mass of the protons and neutrons Identifying ElementsFigure 2.3ProtonNeutronElectronDeuterium (2H)(1p+; 1n0; 1e–)Tritium (3H)(1p+; 2n0; 1e–)Hydrogen (1H)(1p+; 0n0; 1e–)Spontaneous decay (radioactivity)Similar chemistry to stable isotopesCan be detected with scannersRadioisotopesValuable tools for biological research and medicine Cause damage to living tissue: Useful against localized cancers Radon from uranium decay causes lung cancerRadioisotopes Most atoms combine chemically with other atoms to form molecules and compoundsMolecule—two or more atoms of same element bonded together (e.g., H + H = H2 )Compound—two or more atoms of different elements bonded together (e.g., C6H12O6)Molecules and CompoundsMost matter exists as mixturesTwo or more components physically intermixedThree types of mixturesSolutionsColloidsSuspensionsMixtures Solutions are homogeneous mixturesUsually transparent, e.g., atmospheric air or seawater SolventPresent in greatest amount, usually a liquidSolute(s)Present in smaller amountsSolutions Colloids (emulsions)Heterogeneous translucent mixtures, e.g., cytosolLarge solute particles that do not settle outUndergo sol-gel transformationsSuspensions:Heterogeneous mixtures, e.g., bloodLarge visible solutes tend to settle outColloids and SuspensionsFigure 2.4SolutionSoluteparticles Soluteparticles Soluteparticles Solute particles are verytiny, do not settle out orscatter light.ColloidSolute particles are largerthan in a solution and scatterlight; do not settle out.SuspensionSolute particles are verylarge, settle out, and mayscatter light.ExampleMineral waterExampleGelatinExampleBloodMixturesNo chemical bonding between components Can be separated physically, such as by straining or filteringHeterogeneous or homogeneousCompoundsCan be separated only by breaking bondsAll are homogeneousMixtures vs. CompoundsElectrons occupy up to seven electron shells (energy levels) around nucleus Octet rule: Except for the first shell which is full with two electrons, atoms interact in a manner to have eight electrons in their outermost energy level (valence shell)Chemical BondsStable and unreactiveOutermost energy level fully occupied or contains eight electronsChemically Inert ElementsFigure 2.5aHelium (He)(2p+; 2n0; 2e–)Neon (Ne)(10p+; 10n0; 10e–)2e2e8e(a) Chemically inert elementsOutermost energy level (valence shell) completeOutermost energy level not fully occupied by electronsTend to gain, lose, or share electrons (form bonds) with other atoms to achieve stability Chemically Reactive ElementsFigure 2.5b2e4e2e8e1e(b) Chemically reactive elementsOutermost energy level (valence shell) incompleteHydrogen (H)(1p+; 0n0; 1e–)Carbon (C)(6p+; 6n0; 6e–)1eOxygen (O)(8p+; 8n0; 8e–)Sodium (Na)(11p+; 12n0; 11e–)2e6eIonic Covalent HydrogenTypes of Chemical BondsIons are formed by transfer of valence shell electrons between atomsAnions (– charge) have gained one or more electronsCations (+ charge) have lost one or more electronsAttraction of opposite charges results in an ionic bondIonic BondsFigure 2.6a-bSodium atom (Na)(11p+; 12n0; 11e–)Chlorine atom (Cl)(17p+; 18n0; 17e–)Sodium ion (Na+)Chloride ion (Cl–)Sodium chloride (NaCl)+–(a) Sodium gains stability by losing one electron, and chlorine becomes stable by gaining one electron. (b) After electron transfer, the oppositely charged ions formed attract each other. Ionic compounds form crystals instead of individual moleculesNaCl (sodium chloride)Formation of an Ionic BondFigure 2.6cCI–Na+(c) Large numbers of Na+ and Cl– ions associate to form salt (NaCl) crystals. Formed by sharing of two or more valence shell electrons Allows each atom to fill its valence shell at least part of the timeCovalent BondsFigure 2.7a+HydrogenatomsCarbonatomMolecule ofmethane gas (CH4)Structuralformulashows singlebonds.(a) Formation of four single covalent bonds: carbon shares four electron pairs with four hydrogen atoms.orResulting moleculesReacting atomsFigure 2.7borOxygenatomOxygenatomMolecule ofoxygen gas (O2)Structuralformulashowsdouble bond.(b) Formation of a double covalent bond: Two oxygen atoms share two electron pairs.Resulting moleculesReacting atoms+Figure 2.7c+orNitrogenatomNitrogenatomMolecule ofnitrogen gas (N2)Structuralformulashowstriple bond.(c) Formation of a triple covalent bond: Two nitrogen atoms share three electron pairs.Resulting moleculesReacting atomsSharing of electrons may be equal or unequalEqual sharing produces electrically balanced nonpolar moleculesCO2Covalent BondsFigure 2.8aUnequal sharing by atoms with different electron-attracting abilities produces polar molecules H2OAtoms with six or seven valence shell electrons are electronegative, e.g., oxygenAtoms with one or two valence shell electrons are electropositive, e.g., sodiumCovalent BondsFigure 2.8bFigure 2.9Attractive force between electropositive hydrogen of one molecule and an electronegative atom of another moleculeCommon between dipoles such as waterAlso act as intramolecular bonds, holding a large molecule in a three-dimensional shapeHydrogen BondsPLAYAnimation: Hydrogen Bonds(a) The slightly positive ends (+) of the watermolecules become aligned with the slightlynegative ends (–) of other water molecules. +–––––++ ++ +Hydrogen bond(indicated bydotted line)Figure 2.10aOccur when chemical bonds are formed, rearranged, or brokenRepresented as chemical equationsChemical equations contain:Molecular formula for each reactant and product Relative amounts of reactants and products, which should balance Chemical ReactionsH + H  H2 (hydrogen gas)4H + C  CH4 (methane)Examples of Chemical Equations(reactants)(product) Synthesis (combination) reactions Decomposition reactions Exchange reactionsPatterns of Chemical ReactionsA + B  ABAlways involve bond formation AnabolicSynthesis ReactionsFigure 2.11aExampleAmino acids are joined together toform a protein molecule. (a) Synthesis reactionsSmaller particles are bondedtogether to form larger,more complex molecules.Amino acidmoleculesProteinmoleculeAB  A + BReverse synthesis reactionsInvolve breaking of bondsCatabolic Decomposition ReactionsFigure 2.11bExampleGlycogen is broken down to releaseglucose units. Bonds are broken in largermolecules, resulting in smaller,less complex molecules. (b) Decomposition reactionsGlucosemoleculesGlycogenAB + C = AC + BAB + CD = AD + CBAlso called displacement reactionsBonds are both made and brokenExchange ReactionsFigure 2.11cExampleATP transfers its terminal phosphategroup to glucose to form glucose-phosphate.Bonds are both made and broken(also called displacement reactions).(c) Exchange reactionsGlucoseAdenosine triphosphate (ATP)Adenosine diphosphate (ADP)Glucosephosphate++Decomposition reactions: Reactions in which fuel is broken down for energyAlso called exchange reactions because electrons are exchanged or shared differentlyElectron donors lose electrons and are oxidizedElectron acceptors receive electrons and become reducedOxidation-Reduction (Redox) ReactionsAll chemical reactions are either exergonic or endergonicExergonic reactions—release energyCatabolic reactionsEndergonic reactions—form energy bonds: products contain more potential energy than did reactantsAnabolic reactionsChemical ReactionsAll chemical reactions are theoretically reversibleA + B  ABAB  A + BChemical equilibrium occurs if neither a forward nor reverse reaction is dominant Many biological reactions are essentially irreversible due to Energy requirements Removal of productsChemical ReactionsRate of reaction is influenced by: temperature   rate particle size   rate  concentration of reactant   rate Catalysts:  rate without being chemically changed: they reduce the activation energy needed for the reactionEnzymes are biological catalystsRate of Chemical Reactions