Chapter 2Chapter 2

The Chemical Basis of LifeThe Chemical Basis of Life

I. Elements: I. Elements: Substances that can not be broken down into Substances that can not be broken down into

simpler substances by chemical reactions.simpler substances by chemical reactions. There are 92 naturally occurring elements: There are 92 naturally occurring elements:

Oxygen, carbon, nitrogen, calcium, sodium, etc.Oxygen, carbon, nitrogen, calcium, sodium, etc. Life requires about 25 of the 92 elementsLife requires about 25 of the 92 elements Chemical Symbols: Chemical Symbols:

Abbreviations for the name of each element.Abbreviations for the name of each element. Usually one or two letters of the English or Usually one or two letters of the English or

Latin name of the elementLatin name of the element First letter upper case, second letter lower case. First letter upper case, second letter lower case.

Example: Helium (He), sodium (Na), potassium Example: Helium (He), sodium (Na), potassium (K), gold (Au).(K), gold (Au).

Main ElementsMain Elements: Over: Over 98% 98% of an organism’s of an organism’s mass is made up ofmass is made up of six elements. six elements. OxygenOxygen (O): 65% body mass (O): 65% body mass

Cellular respiration, component of water, and most Cellular respiration, component of water, and most organic compounds.organic compounds.

CarbonCarbon (C): 18% of body mass. (C): 18% of body mass. Backbone of all organic compounds.Backbone of all organic compounds.

HydrogenHydrogen (H): 10% of body mass. (H): 10% of body mass. Component of water and most organic compounds.Component of water and most organic compounds.

NitrogenNitrogen (N): 3% of body mass. (N): 3% of body mass. Component of proteins and nucleic acids (DNA/RNA)Component of proteins and nucleic acids (DNA/RNA)

CalciumCalcium (Ca): 1.5% of body mass. (Ca): 1.5% of body mass. Bones, teeth, clotting, muscle and nerve function.Bones, teeth, clotting, muscle and nerve function.

PhosphorusPhosphorus ( (PP): 1% of body mass): 1% of body mass Bones, nucleic acids, energy transfer (ATP).Bones, nucleic acids, energy transfer (ATP).

Minor Elements: Minor Elements: Found in low amounts. Found in low amounts. Between 1% and 0.01%. Between 1% and 0.01%. PotassiumPotassium (K): Main positive ion inside cells. (K): Main positive ion inside cells.

Nerve and muscle function.Nerve and muscle function.

SulfurSulfur (S): Component of most proteins. (S): Component of most proteins. SodiumSodium (Na): Main positive ion outside cells. (Na): Main positive ion outside cells.

Fluid balance, nerve function.Fluid balance, nerve function.

ChlorineChlorine (Cl): Main negative ion outside cells. (Cl): Main negative ion outside cells. Fluid balance.Fluid balance.

MagnesiumMagnesium (Mg): Component of many (Mg): Component of many enzymes and chlorophyll.enzymes and chlorophyll.

Trace elements: Trace elements: Less than 0.01% of mass:Less than 0.01% of mass: BoronBoron ((BB)) ChromiumChromium ((CrCr)) CobaltCobalt ((CoCo)) CopperCopper ((CuCu)) IronIron ((FeFe)) FluorineFluorine ( (FF)) IodineIodine ( (II)) ManganeseManganese ( (MnMn)) MolybdenumMolybdenum ( (MoMo)) SeleniumSelenium ( (SeSe)) SiliconSilicon ( (SiSi)) TinTin ( (SnSn)) VanadiumVanadium ( (VV)) ZincZinc ( (ZnZn) )

II. Structure & Properties of AtomsII. Structure & Properties of AtomsAtoms: Atoms: Smallest particle of an element that Smallest particle of an element that retains its chemical properties. Made up of retains its chemical properties. Made up of three main subatomic particles.three main subatomic particles.

ParticleParticle LocationLocation MassMass ChargeChargeProtonProton (p (p++) In nucleus ) In nucleus 1 +1 1 +1

NeutronNeutron (n (noo) In nucleus ) In nucleus 1 0 1 0

ElectronElectron (e (e--) Outside nucleus ) Outside nucleus 0 0** -1 -1

** Mass is negligible for our purposes. Mass is negligible for our purposes.

Atomic Particles: Protons, Neutrons, and Electrons

Helium Atom Carbon Atom

Structure and Properties of AtomsStructure and Properties of Atoms1. Atomic number1. Atomic number = # protons = # protons The number of protons is The number of protons is uniqueunique for each for each elementelement Each element has a fixed number of protons in its Each element has a fixed number of protons in its

nucleus. This number will nucleus. This number will nevernever change for a change for a given element.given element.

Written as a Written as a subscriptsubscript to left of element symbol. to left of element symbol.

Examples: Examples: 66C, C, 88O, O, 1616S, S, 2020CaCa

Because atoms are electrically neutral (no Because atoms are electrically neutral (no charge), the charge), the numbernumber of of electronselectrons andand protonsprotons are are always the same.always the same.

In the periodic table elements are organized by In the periodic table elements are organized by increasingincreasing atomic number. atomic number.

Structure and Structure and Properties of Atoms:Properties of Atoms:2. Mass number2. Mass number = # protons + # neutrons = # protons + # neutrons Gives the mass of a specific atom.Gives the mass of a specific atom. Written as a Written as a superscriptsuperscript to the left of the element to the left of the element

symbol.symbol.

Examples: Examples: 1212C, C, 1616O, O, 3232S, S, 4040Ca. Ca. The number of protons for an element is always The number of protons for an element is always

the same, but the number of neutrons may vary.the same, but the number of neutrons may vary. The number of neutrons can be determined by: The number of neutrons can be determined by:

# neutrons = Mass number - Atomic number# neutrons = Mass number - Atomic number

Structure and Structure and Properties of Atoms:Properties of Atoms:

3. Isotopes3. Isotopes:: Variant forms of the same element. Variant forms of the same element. Isotopes have Isotopes have differentdifferent numbers of numbers of neutronsneutrons and and

therefore different therefore different massesmasses.. Isotopes have the Isotopes have the samesame numbers of numbers of protonsprotons and and

electronselectrons.. Example: In nature there are three forms or Example: In nature there are three forms or

isotopes of carbon (isotopes of carbon (66C):C): 1212C: About 99% of atoms. Have 6 pC: About 99% of atoms. Have 6 p++, , 6 n6 noo, and 6 e, and 6 e--.. 1313C: About 1% of atoms. Have 6 pC: About 1% of atoms. Have 6 p++, , 7 n7 noo, and 6 e, and 6 e--. . 1414C: Found in tiny quantities. Have 6 pC: Found in tiny quantities. Have 6 p++, , 8 n8 noo, and 6 e, and 6 e--. .

RadioactiveRadioactive form (unstable). Used for form (unstable). Used for datingdating fossils. fossils.

Electrons determine how an atom can bond Electrons determine how an atom can bond with other atomswith other atoms

A. A. Energy levels Energy levels: Electrons occupy different : Electrons occupy different energy levels around the nucleus. energy levels around the nucleus.

Level (Shell)Level (Shell) Electron CapacityElectron Capacity

11 2 (2 (Closest to nucleus, lowest energy)Closest to nucleus, lowest energy)

22 88

33 8 8 (If valence shell, 18 otherwise)(If valence shell, 18 otherwise)

4, 5, & 64, 5, & 6 18 18

B. B. Electron configuration:Electron configuration: Arrangement of Arrangement of

electrons in orbitals around nucleus of atom.electrons in orbitals around nucleus of atom.

C. C. Valence ElectronsValence Electrons: Number of electrons in : Number of electrons in

outerouter energy shell of an atom. energy shell of an atom.

Electron Arrangements of Important Elements of Life

1 Valence electron 4 Valence electrons 5 Valence electrons 6 Valence electrons

III. How Atoms Form Molecules: III. How Atoms Form Molecules: Chemical BondsChemical Bonds

MoleculeMolecule: : Two or more atoms combined chemically.Two or more atoms combined chemically.CompoundCompound: A substance with two or more elements : A substance with two or more elements

combined in a fixed ratio.combined in a fixed ratio. Water (HWater (H22O)O) Hydrogen peroxide (HHydrogen peroxide (H22OO22)) Carbon dioxide (COCarbon dioxide (CO22)) Carbon monoxide (CO)Carbon monoxide (CO) Table salt (NaCl)Table salt (NaCl)

Atoms are linked by Atoms are linked by chemical bonds.chemical bonds.Chemical FormulaChemical Formula:: Describes the chemical Describes the chemical

composition of a molecule of a compound. composition of a molecule of a compound. Symbols indicate the type of atomsSymbols indicate the type of atoms Subscripts indicate the number of atomsSubscripts indicate the number of atoms

How Atoms Form Molecules: How Atoms Form Molecules: Chemical BondsChemical Bonds

““Octet Rule”Octet Rule”: When the outer shell of an atom : When the outer shell of an atom is not full, i.e.: contains fewer than 8 (or 2) is not full, i.e.: contains fewer than 8 (or 2) electrons (electrons (valence e-valence e-),), the atom tends to gain, the atom tends to gain, lose, or share electrons to achieve a complete lose, or share electrons to achieve a complete outer shell (8, 2, or 0) electrons.outer shell (8, 2, or 0) electrons.

ExampleExample: : Sodium has 11 electrons, 1 valence electron.Sodium has 11 electrons, 1 valence electron.Sodium Sodium losesloses its electron, becoming an ion: its electron, becoming an ion:NaNa ------->-------> NaNa++ + + 1 e1 e--

1(2), 2(8), 1(2), 2(8), 3(1)3(1) 1(2), 2(8)1(2), 2(8)Outer shell has 1 eOuter shell has 1 e-- Outer shell is fullOuter shell is fullSodium atomSodium atom Sodium ionSodium ion

Number of valence electrons determine the Number of valence electrons determine the chemical behavior of atoms.chemical behavior of atoms.

ElementElement ValenceValence CombiningCombiningTendencyTendency

ElectronsElectrons CapacityCapacity

SodiumSodium 11 11 LoseLose 1 1

CalciumCalcium 22 22 LoseLose 2 2

AluminumAluminum 33 33 LoseLose 3 3

CarbonCarbon 44 44 ShareShare 4 4

NitrogenNitrogen 55 33 GainGain 3 3

OxygenOxygen 66 22 GainGain 2 2

ChlorineChlorine 77 11 GainGain 1 1

NeonNeon** 88 00 StableStable

* Noble gas* Noble gas

How Atoms Form Molecules: How Atoms Form Molecules: Chemical BondsChemical Bonds

Atoms can lose, gain, or share electrons to satisfy Atoms can lose, gain, or share electrons to satisfy

octet rule octet rule (fill outermost shell).(fill outermost shell).

Two main types of Chemical BondsTwo main types of Chemical Bonds

A. A. Ionic bondIonic bond: Atoms : Atoms gaingain or or loselose electrons electrons

B. B. Covalent bondCovalent bond: Atoms : Atoms shareshare electrons electrons

A. A. Ionic Bond:Ionic Bond: Atoms gain or lose electrons. Atoms gain or lose electrons. Bonds are attractions between Bonds are attractions between ionsions of opposite of opposite charge.charge.

Ionic compoundIonic compound: One consisting of ionic bonds.: One consisting of ionic bonds.

Na + Cl ----------> Na + Cl ----------> NaNa++ Cl Cl--

sodium chlorine Table saltsodium chlorine Table salt

(Sodium (Sodium chloride)chloride)

Two Types of Ions:Two Types of Ions:

Anions:Anions: Negatively charged particle ( Negatively charged particle (ClCl--))

Cations:Cations: Positively charged particle ( Positively charged particle (NaNa++))

Ionic Bonding: Sodium Chloride

A Crystal of Sodium Chloride:Ions are Held Together by Ionic Bonds

B. B. Covalent BondCovalent Bond: Involves the “: Involves the “sharingsharing” of one ” of one or more pairs of electrons between atoms.or more pairs of electrons between atoms.

Covalent compoundCovalent compound: One consisting of : One consisting of covalent bonds.covalent bonds.

ExampleExample: Methane (CH: Methane (CH44): Main component ): Main component

of natural gas.of natural gas.

HH ||

H---C---HH---C---H ||HH

Each line represents on shared pair of electrons.Each line represents on shared pair of electrons.Octet rule is satisfiedOctet rule is satisfied: Carbon has 8 electrons,: Carbon has 8 electrons,Hydrogen has 2 electronsHydrogen has 2 electrons

There may be more than one covalent bond between There may be more than one covalent bond between atoms:atoms:

1. 1. Single bond:Single bond: One electron pair is shared between One electron pair is shared between two atoms.two atoms.Example: Chlorine (ClExample: Chlorine (Cl22), water (H), water (H22O); methane O); methane (CH(CH44))

Cl --- ClCl --- Cl

2. 2. Double bond:Double bond: Two electron pairs share between Two electron pairs share between atoms.atoms.Example: Oxygen gas (OExample: Oxygen gas (O22); carbon dioxide (CO); carbon dioxide (CO22))

O=OO=O3. 3. Triple bondTriple bond:: Three electron pairs shared between Three electron pairs shared between

two atoms.two atoms.Example: Nitrogen gas (NExample: Nitrogen gas (N22))

N = NN = N

----

Single and Double Covalent Bonds

Number of covalent bonds formed Number of covalent bonds formed by important elementsby important elements: :

Carbon (4) Carbon (4)

Nitrogen (3)Nitrogen (3)

Oxygen (2)Oxygen (2)

Sulfur (2)Sulfur (2)

Hydrogen (1)Hydrogen (1)

Two Types of Covalent Bonds: Polar and Two Types of Covalent Bonds: Polar and NonpolarNonpolar

ElectronegativityElectronegativity: : A measure of an atom’s A measure of an atom’s ability to attract and hold onto a shared ability to attract and hold onto a shared pair of electrons.pair of electrons.Some atoms such as Some atoms such as oxygenoxygen or or nitrogennitrogen have a much higher electronegativity have a much higher electronegativity than others, such as carbon and than others, such as carbon and hydrogen.hydrogen.

ElementElement ElectronegativityElectronegativityOO 3.53.5NN 3.03.0

S & CS & C 2.52.5P & HP & H 2.12.1

Polar and Nonpolar Covalent BondsPolar and Nonpolar Covalent Bonds

A.A. Nonpolar Covalent Bond:Nonpolar Covalent Bond: When the When the atoms in a bond have equal or similar atoms in a bond have equal or similar attraction for the electrons attraction for the electrons (electronegativity), they are shared (electronegativity), they are shared equallyequally. .

Example: OExample: O22, H, H22, Cl, Cl22

Nonpolar Covalent Bonds: Electrons are Shared Equally

Polar and Nonpolar Covalent BondsPolar and Nonpolar Covalent Bonds

B. B. Polar Covalent BondPolar Covalent Bond: When the atoms : When the atoms in a bond have different in a bond have different electronegativities, the electrons are electronegativities, the electrons are shared shared unequallyunequally. .

Electrons are closer to the more Electrons are closer to the more electronegative atom creating a polarity electronegative atom creating a polarity or partial charge.or partial charge.

Example: HExample: H22OOOxygen has a partial negative charge.Oxygen has a partial negative charge.Hydrogens have partial positive charges.Hydrogens have partial positive charges.

Polar Covalent Bonds: Electrons are Shared Unequally Creating Partial Charges

Water Molecule

Other Bonds: Weak chemical bonds are Other Bonds: Weak chemical bonds are important in the chemistry of living things.important in the chemistry of living things.

Hydrogen bondsHydrogen bonds: : Attraction between theAttraction between the partially positive H of one molecule partially positive H of one molecule and aand a partially negative atom of anotherpartially negative atom of another

Hydrogen bonds are about 20 X easier to Hydrogen bonds are about 20 X easier to break than a normal covalent bond.break than a normal covalent bond.

Responsible for many properties of water.Responsible for many properties of water. Determine 3 dimensional shape of DNA and Determine 3 dimensional shape of DNA and

proteins.proteins. Chemical signaling (molecule to receptor).Chemical signaling (molecule to receptor).

Hydrogen Bonds: Weak Attractions between Hydrogen and Partially Negative Atoms

Water Molecules

Water: A Unique Compound for Water: A Unique Compound for LifeLife

Water: The Ideal Compound for LifeWater: The Ideal Compound for Life

Living cells are 70-90% waterLiving cells are 70-90% water

Water covers 3/4 of earth’s surfaceWater covers 3/4 of earth’s surface

Water is the ideal solvent for chemical Water is the ideal solvent for chemical

reactionsreactions

On earth, water exists as gas, liquid, and On earth, water exists as gas, liquid, and

solidsolid

I. Polarity of water causes hydrogen bondingI. Polarity of water causes hydrogen bonding

Water molecules are held together by H-bondingWater molecules are held together by H-bonding

Partially positive H attracted to partially Partially positive H attracted to partially

negative O atom.negative O atom.

Individual H bond are weak, but the cumulative effect Individual H bond are weak, but the cumulative effect

of many H bonds is very strong.of many H bonds is very strong.

H bonds only last a fraction of a second, but at any H bonds only last a fraction of a second, but at any

moment most molecules are hydrogen bonded to moment most molecules are hydrogen bonded to

others.others.

Hydrogen Bonds in Water are Responsible for Many of its Properties

Unique properties of water caused by H-bondsUnique properties of water caused by H-bonds

Cohesion:Cohesion: Water molecules stick to each other. Water molecules stick to each other.

This causes This causes surface tensionsurface tension.. Film-like surface of water is difficult to break.Film-like surface of water is difficult to break.

Used by some insects that live on water surface.Used by some insects that live on water surface.

Water forms beads.Water forms beads.

Adhesion:Adhesion: Water sticks to many surfaces.Water sticks to many surfaces.

Capillary Action:Capillary Action: Water tends to rise in narrow Water tends to rise in narrow tubes. This is caused bytubes. This is caused by cohesioncohesion and and adhesion adhesion (water molecules stick to walls of tubes).(water molecules stick to walls of tubes).

ExamplesExamples: : Upward movement of water through Upward movement of water through plant vessels and fluid in blood vessels.plant vessels and fluid in blood vessels.

Unique properties of water caused by H-bondsUnique properties of water caused by H-bonds

ExpandsExpands when it freezes. when it freezes. Ice forms stable H bonds, each molecule is bonded to Ice forms stable H bonds, each molecule is bonded to

four neighbors (crystalline lattice). Water does not four neighbors (crystalline lattice). Water does not

form stable H bonds.form stable H bonds.

Ice is less dense than water.Ice is less dense than water.

Ice floats on water.Ice floats on water.

Life can survive in bodies of water, even though the Life can survive in bodies of water, even though the

earth has gone through many winters and ice agesearth has gone through many winters and ice ages

Ice Forms Stable Hydrogen Bonds and is Less Dense than Water

Unique properties of water caused by H-bondsUnique properties of water caused by H-bonds

StableStable TemperatureTemperature:: Water resists changes in Water resists changes in

temperature because it temperature because it has a high has a high specific heat.specific heat. Specific HeatSpecific Heat: : Amount of heat energy needed to raise Amount of heat energy needed to raise

1 g of substance 1 degree Celsius 1 g of substance 1 degree Celsius

• Specific Heat of Water:Specific Heat of Water: 1 calorie/gram/ 1 calorie/gram/ooCC

High heat of vaporizationHigh heat of vaporization: Water must absorb large : Water must absorb large

amounts of energy (heat) to evaporate.amounts of energy (heat) to evaporate.

• Heat of Vaporization of Water:Heat of Vaporization of Water: 540 calorie/gram. 540 calorie/gram.

Evaporative cooling is used by many organisms to Evaporative cooling is used by many organisms to

regulate body temperature.regulate body temperature.

• SweatingSweating

• PantingPanting

Unique properties of water caused by H-bondsUnique properties of water caused by H-bonds

Universal SolventUniversal Solvent: Dissolves many (but not all) : Dissolves many (but not all)

substances to form substances to form solutionssolutions. .

SolutionsSolutions are homogeneous mixtures of two or are homogeneous mixtures of two or

more substances (salt water, air, tap water). more substances (salt water, air, tap water).

All solutions have at least two components:All solutions have at least two components: SolventSolvent: Dissolving substance (water, alcohol, oil).: Dissolving substance (water, alcohol, oil).

• Aqueous solutionAqueous solution: If solvent is water.: If solvent is water.

SoluteSolute: Substance that is dissolved (salt, sugar, CO: Substance that is dissolved (salt, sugar, CO22).).

• Water dissolves polar and ionic solutes well.Water dissolves polar and ionic solutes well.

• Water does not dissolve nonpolar solvents well.Water does not dissolve nonpolar solvents well.

A Salt Crystal Dissolving in Water

Solubility of a Solute Depends on its Solubility of a Solute Depends on its Chemical NatureChemical Nature

SolubilitySolubility: : Ability of substance to dissolve in a Ability of substance to dissolve in a

given solvent.given solvent.

Two Types of Solutes:Two Types of Solutes:

A. HydrophilicA. Hydrophilic:: “Water loving” dissolve easily “Water loving” dissolve easily in water.in water. Ionic compounds (e.g. salts)Ionic compounds (e.g. salts) Polar compounds (molecules with polar regions)Polar compounds (molecules with polar regions) Examples: Compounds with -OH groups Examples: Compounds with -OH groups

(alcohols).(alcohols). ““Like dissolves in like”Like dissolves in like”

Solubility of a Solute Depends on its Solubility of a Solute Depends on its Chemical NatureChemical Nature

Two Types of Solutes:Two Types of Solutes:

B. HydrophobicB. Hydrophobic: : “Water fearing” do not “Water fearing” do not dissolve in waterdissolve in water Non-polar compounds (lack polar regions)Non-polar compounds (lack polar regions)

ExamplesExamples: Hydrocarbons with only C-H non-polar : Hydrocarbons with only C-H non-polar

bonds, oils, gasoline, waxes, fats, etc.bonds, oils, gasoline, waxes, fats, etc.

ACIDS, BASES, pH AND BUFFERSACIDS, BASES, pH AND BUFFERSA. AcidA. Acid: : A substance that donates protons (HA substance that donates protons (H++). ). Separate into one or more protons and an Separate into one or more protons and an

anion:anion:

HCl (into HCl (into HH22OO ) -------> H ) -------> H++ + Cl + Cl--

HH22SOSO44 (into (into HH22OO ) --------> H ) --------> H++ + HSO + HSO44--

Acids Acids INCREASEINCREASE the relative [H the relative [H++] of a ] of a solution.solution.

Water can also dissociate into ions, at low Water can also dissociate into ions, at low levels:levels:

HH22O <======> HO <======> H++ + OH + OH--

B. BaseB. Base: : A substance that accepts protons (HA substance that accepts protons (H++). ). Many bases separate into one or more positive Many bases separate into one or more positive

ions (cations) and a hydroxyl group (ions (cations) and a hydroxyl group (OHOH-- ).). Bases Bases DECREASEDECREASE the relative [H the relative [H++] of a ] of a

solution solution ( and increases the relative [OH( and increases the relative [OH--] ).] ).

HH22O <======> HO <======> H++ + OH + OH--

DirectlyDirectly NHNH33 + H + H++ <=------> NH <=------> NH44++

IndirectlyIndirectly NaOH ---------> Na NaOH ---------> Na++ + OH + OH--

( H( H++ + + OHOH-- <=====> H <=====> H22O )O )

Strong acids and basesStrong acids and bases: : Dissociation is almost Dissociation is almost complete (99% or more of molecules).complete (99% or more of molecules).

HCl (aq) -------------> HHCl (aq) -------------> H++ + Cl + Cl- -

NaOH (aq) -----------> NaNaOH (aq) -----------> Na++ + OH + OH--

(L.T. 1% in this form)(L.T. 1% in this form) (G.T. 99% in dissociated form) (G.T. 99% in dissociated form)

A relatively small amount of a strong acid or base A relatively small amount of a strong acid or base will drastically affect the pH of solution.will drastically affect the pH of solution.

Weak acids and basesWeak acids and bases: : A small percentage of A small percentage of molecules dissociate at a give time (1% or less)molecules dissociate at a give time (1% or less)

HH22COCO33 <=====> H <=====> H++ + HCO + HCO33--

carbonic acid Bicarbonate ioncarbonic acid Bicarbonate ion(G.T. 99% in this form)(G.T. 99% in this form) (L.T. 1% in dissociated form) (L.T. 1% in dissociated form)

C. pH scale: C. pH scale: [H[H++] and [OH] and [OH--]] pH scale is used to measure how basic or acidic pH scale is used to measure how basic or acidic

a solution is.a solution is. Range of pH scaleRange of pH scale: 0 through 14.: 0 through 14.

Neutral solutionNeutral solution: pH is 7.: pH is 7. [H[H++ ] = [OH ] = [OH--]]

Acidic solutionAcidic solution: : pH is less than 7. pH is less than 7. [H[H++ ] > [OH ] > [OH--]]

Basic solutionBasic solution: : pH is greater than 7. pH is greater than 7. [H[H++ ] < [OH ] < [OH--]]

As [HAs [H++] increases pH decreases (inversely ] increases pH decreases (inversely

proportional).proportional).

Logarithmic scale:Logarithmic scale: Each unit on the pH scale Each unit on the pH scale

represents a ten-fold change in [H+].represents a ten-fold change in [H+].

pH of Common Solutions

D. Buffers keep pH of solutions relatively D. Buffers keep pH of solutions relatively constantconstant

BufferBuffer:: Substance which prevents sudden Substance which prevents sudden large changes in pH when acids or bases are large changes in pH when acids or bases are added.added.

Buffers are biologically important because Buffers are biologically important because most of the chemical reactions required for life most of the chemical reactions required for life can only take place within narrow pH ranges.can only take place within narrow pH ranges.

Example: Example: Normal blood pH 7.35-7.45. Serious health Normal blood pH 7.35-7.45. Serious health

problems will arise if blood pH is not stable.problems will arise if blood pH is not stable.

CHEMICAL REACTIONSCHEMICAL REACTIONS

A chemical change in which sA chemical change in which substances ubstances ((reactantsreactants) are joined, broken down, or ) are joined, broken down, or rearranged to form new substances (rearranged to form new substances (productsproducts).).

Involve the making and/or breaking of Involve the making and/or breaking of chemical bonds.chemical bonds.

Chemical equations are used to represent Chemical equations are used to represent chemical reactions.chemical reactions.

ExampleExample::

2 H2 H22 ++ OO22 -----------> 2H -----------> 2H22OO

2 Hydrogen Oxygen 2 Hydrogen Oxygen 2 Water2 WaterMoleculesMolecules Molecule Molecule MoleculesMolecules

Chemical Reactions Require Making and Breaking Bonds