1Basic ChemistryBasic Chemistry

Ch. 2 OutlineCh. 2 Outline

Basic ChemistryBasic Chemistry

2Basic ChemistryBasic Chemistry

Chemical ElementsChemical Elements

MatterMatter::Anything that has mass and occupies spaceAnything that has mass and occupies space

Only 92 naturally occurring Only 92 naturally occurring elementselements

Organisms composed primarily (95%) of only Organisms composed primarily (95%) of only six elementssix elementsCarbon, Hydrogen, Nitrogen, Oxygen, Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, SulfurPhosphorus, Sulfur

CHNOPSCHNOPS

3

Composition of Earth’s Crustversus Organisms

4Basic ChemistryBasic Chemistry

Atomic StructureAtomic Structure

AtomsAtoms - Smallest particles of elements - Smallest particles of elementsAtoms composed of three types of subatomic Atoms composed of three types of subatomic

particlesparticlesProtonsProtons­ Positive chargePositive charge­ In nucleusIn nucleus

NeutronsNeutrons­ Neutral chargeNeutral charge­ Also found in nucleusAlso found in nucleus

ElectronsElectrons­ Negative chargeNegative charge­ Orbit nucleusOrbit nucleus

5Basic ChemistryBasic Chemistry

Atomic SymbolsAtomic Symbols

Each element represented by unique atomic Each element represented by unique atomic symbolsymbolFirst letter capitalizedFirst letter capitalized

Superscripted numberSuperscripted number::

­ Represents mass numberRepresents mass number

­ Count of protons plus count of neutronsCount of protons plus count of neutrons

Subscripted numberSubscripted number::

­ Represents atomic numberRepresents atomic number

­ Number of protons in nucleusNumber of protons in nucleus

MassMassNumberNumber

AtomicAtomicNumberNumber

AtomicAtomicSymbolSymbol

126

Carbon

C

6Basic ChemistryBasic Chemistry

Periodic TablePeriodic Table

Elements grouped in periodic table based on Elements grouped in periodic table based on characteristicscharacteristicsVertical columns = groups; chemically similarVertical columns = groups; chemically similar

1

H1.008

3

Li6.941

11

Na22.99

19

K39.10

4

Be9.012

12

Mg24.31

20

Ca40.08

5

B10.81

13

Al26.98

21

Ga69.72

6

C12.01

14

Si28.09

22

Ge72.59

7

N14.01

15

P30.97

23

As74.92

8

O16.00

16

S32.07

24

Se78.96

9

F19.00

17

Cl35.45

25

Br79.90

10

Ne20.18

18

Ar39.95

26

Kr83.60

2

He4.003

II

IIII IIIIII IVIV VV VIVI VIIVII

VIIIVIII

11

22

33

44

Groups

Periods

7Basic ChemistryBasic Chemistry

IsotopesIsotopes

IsotopesIsotopes::

Atoms of the same element with a differing Atoms of the same element with a differing numbers of neutronsnumbers of neutrons

Some isotopes spontaneously decaySome isotopes spontaneously decay

­ RadioactiveRadioactive

­ Give off energy in the form of rays and Give off energy in the form of rays and subatomic particlessubatomic particles

­ Can be used as tracersCan be used as tracers

­MutagenicMutagenic – Can cause cancer – Can cause cancer

126

Carbon 12C 13

6

Carbon 13C 14

6

Carbon 14C

8Some Medical Uses forLow Level Radiation

9Some Medical Uses forHigh Level Radiation

10Basic ChemistryBasic ChemistryElectron Shells, OrbitalsElectron Shells, Orbitalsand Energy Levelsand Energy Levels

Atoms normally have as many electrons as Atoms normally have as many electrons as protonsprotons

Opposite charges balance leaving atom Opposite charges balance leaving atom neutralneutral

Electrons are attracted to the positive nucleusElectrons are attracted to the positive nucleusRevolve around nucleus in orbitalsRevolve around nucleus in orbitalsCan be pushed into higher orbitals with Can be pushed into higher orbitals with energyenergy

Release that energy when they fall back to Release that energy when they fall back to lower orbitallower orbital

Different energy levels referred to as electron Different energy levels referred to as electron shellsshells

11Basic ChemistryBasic ChemistryThe The Octet RuleOctet Rule for forDistribution of ElectronsDistribution of Electrons

Bohr modelsBohr models show show electron shellselectron shells as as concentric circles around nucleusconcentric circles around nucleus

Each shell has two or more Each shell has two or more electron orbitalselectron orbitals

­ Innermost shell has two orbitalsInnermost shell has two orbitals

­ Others have 8 or multiples thereofOthers have 8 or multiples thereof

Atoms with fewer than 8 electrons in Atoms with fewer than 8 electrons in outermost shell are chemically reactiveoutermost shell are chemically reactive

If 3 or less – Tendency to If 3 or less – Tendency to donatedonate electrons electrons

If 5 or more – Tendency to If 5 or more – Tendency to receivereceive electrons electrons

12Bohr Models of Atoms

13Periodic Table (Revisited)

Vertical columns indicatenumber of electronsin outermost shell

1

H1.008

3

Li6.941

11

Na22.99

19

K39.10

4

Be9.012

12

Mg24.31

20

Ca40.08

5

B10.81

13

Al26.98

21

Ga69.72

6

C12.01

14

Si28.09

22

Ge72.59

7

N14.01

15

P30.97

23

As74.92

8

O16.00

16

S32.07

24

Se78.96

9

F19.00

17

Cl35.45

25

Br79.90

10

Ne20.18

18

Ar39.95

26

Kr83.60

2

He4.003

1

2

3

4

Horizontal periods indicate

total number

of electron shells

I

II III IV V VI VII

VIII

14Basic ChemistryBasic Chemistry

Elements and CompoundsElements and Compounds

MoleculeMolecule - Two or more atoms bonded - Two or more atoms bonded together by covalent bondstogether by covalent bonds If all atoms in molecule are of the same If all atoms in molecule are of the same elementelement­Material is still an elementMaterial is still an element

­ OO22, H, H22, N, N22, etc., etc.

If at least one atom is from a different elementIf at least one atom is from a different element­Material formed is a Material formed is a compoundcompound

­ COCO22, H, H22O, CO, C66HH1212OO66, etc., etc.

­ Characteristics dramatically different from Characteristics dramatically different from constituent elementsconstituent elements

15Basic ChemistryBasic Chemistry

Chemical BondingChemical Bonding

Bonds between atoms are caused by Bonds between atoms are caused by electrons in outermost shellselectrons in outermost shells

The process of bond formation is called a The process of bond formation is called a chemical reactionchemical reaction

Atoms “want” 8 electrons in outer shellAtoms “want” 8 electrons in outer shell

If have < 4 outers, desire to donate themIf have < 4 outers, desire to donate them If have > 4 outers, desire to receive moreIf have > 4 outers, desire to receive more

16Basic ChemistryBasic ChemistryTypes of Bonds:Types of Bonds:Ionic BondingIonic Bonding

Sodium:Sodium:Has 1 outer electronHas 1 outer electron

Chlorine:Chlorine:Has 7 outer electronsHas 7 outer electrons

In reaction, Na completely gives up its In reaction, Na completely gives up its outer electron to Clouter electron to ClNa now a positive ion and Cl a negative ionNa now a positive ion and Cl a negative ionDissimilar charges now bind ions togetherDissimilar charges now bind ions togetherForms sodium chlorideForms sodium chloride­An An ionic compoundionic compound­NaCl table salt)NaCl table salt)

17Formation of Sodium Chloride

18Basic ChemistryBasic ChemistryTypes of Bonds:Types of Bonds:Covalent BondsCovalent Bonds

When atoms are horizontally closer together in the When atoms are horizontally closer together in the periodic tableperiodic table

The electrons are not permanently transferred from The electrons are not permanently transferred from one atom to the other like in NaClone atom to the other like in NaCl

A pair of electrons from the outer shell will “time A pair of electrons from the outer shell will “time share” with one atom and then the othershare” with one atom and then the other

This also causes the atoms to remain togetherThis also causes the atoms to remain together

Known as Known as covalent bondingcovalent bonding

Sometimes two pairs of electrons are shared Sometimes two pairs of electrons are shared between atoms – a between atoms – a double covalent bonddouble covalent bond

19Covalently Bonded Molecules

20Basic ChemistryBasic Chemistry

Nonpolar Covalent BondsNonpolar Covalent Bonds

Consider two elements that are equidistant Consider two elements that are equidistant from the edges of the periodic tablefrom the edges of the periodic tableAtoms will have about equal affinity for Atoms will have about equal affinity for electronselectrons

When bonded covalently:When bonded covalently:

­ The bond electrons will spend about equal time The bond electrons will spend about equal time with both atomswith both atoms­ Such covalent bonds are said to be Such covalent bonds are said to be nonpolarnonpolar

21Basic ChemistryBasic Chemistry

Polar Covalent BondsPolar Covalent Bonds

Consider two elements with one much Consider two elements with one much closer to the edge of the table than the closer to the edge of the table than the otherotherAtoms will have unequal affinity for Atoms will have unequal affinity for electronselectrons

The bond electrons will spend more time The bond electrons will spend more time with one atom than the otherwith one atom than the other­ The atom that gets the most time with the The atom that gets the most time with the electrons will be slightly negativeelectrons will be slightly negative­ The other will be slightly positiveThe other will be slightly positive

Such covalent bonds are said to be Such covalent bonds are said to be polarpolar

22Basic ChemistryBasic ChemistryTypes of Bonds:Types of Bonds:Hydrogen BondsHydrogen Bonds

Water (HWater (H22O or H–O–H) is a polar moleculeO or H–O–H) is a polar molecule

Electrons spend more time with O than H’sElectrons spend more time with O than H’s

H’s become slightly H’s become slightly ++, O slightly , O slightly ––

When polar molecules are dissolved in waterWhen polar molecules are dissolved in water

The H’s of water molecules are attracted to the The H’s of water molecules are attracted to the negative parts of the solute moleculesnegative parts of the solute molecules

Results in a weak bond Results in a weak bond – – the the hydrogen bondhydrogen bond

Easily broken, but many together can be quite Easily broken, but many together can be quite strongstrong

23Water Molecule

24Hydrogen Bonding

25Basic ChemistryBasic ChemistryThe Chemistry of Water:The Chemistry of Water:Heat CapacityHeat Capacity

Water has a high heat capacityWater has a high heat capacity TemperatureTemperature = rate of vibration of molecules = rate of vibration of molecules Apply heat to liquidApply heat to liquid­ Molecules bounce fasterMolecules bounce faster­ Increases temperatureIncreases temperature

But, when heat applied to waterBut, when heat applied to water­ Hydrogen bonds restrain bouncingHydrogen bonds restrain bouncing­ Temperature rises more slowly per unit heatTemperature rises more slowly per unit heat­ Water at a given temp. has more heat than most liquidsWater at a given temp. has more heat than most liquids

Thermal inertiaThermal inertia – resistance to temperature change – resistance to temperature change More heat required to raise water one degree than most More heat required to raise water one degree than most

other liquids (1 calorie per gram)other liquids (1 calorie per gram) Also, more heat is extracted/released when lowering Also, more heat is extracted/released when lowering

water one degree than most other liquidswater one degree than most other liquids

26Basic ChemistryBasic ChemistryProperties of Water:Properties of Water:Heat of VaporizationHeat of Vaporization

High heat of vaporizationHigh heat of vaporization

To raise water from 98 to 99 ºC; ~1 calorieTo raise water from 98 to 99 ºC; ~1 calorie

To raise water from 99 to 100 ºC; ~1 calorieTo raise water from 99 to 100 ºC; ~1 calorie

However, large numbers of hydrogen bonds must be However, large numbers of hydrogen bonds must be broken to evaporate waterbroken to evaporate water

To raise water from 100 to 101 ºC; ~540 calories!To raise water from 100 to 101 ºC; ~540 calories!

This is why sweating (and panting) coolsThis is why sweating (and panting) cools

Evaporative cooling is best when humidity is low Evaporative cooling is best when humidity is low because evaporation occurs rapidlybecause evaporation occurs rapidly

Evaporative cooling works poorest when humidity is Evaporative cooling works poorest when humidity is high because evaporation occurs slowlyhigh because evaporation occurs slowly

27Evaporative Cooling

of Animals

28Basic ChemistryBasic ChemistryProperties of Water:Properties of Water:Heat of FusionHeat of Fusion

Heat of fusionHeat of fusion (melting) (melting)To raise ice from -2 to -1 ºC; ~1 calorieTo raise ice from -2 to -1 ºC; ~1 calorieTo raise water from -1 to 0 ºC; ~1 calorieTo raise water from -1 to 0 ºC; ~1 calorieTo raise water from 0 to 1 ºC; ~80 calories!To raise water from 0 to 1 ºC; ~80 calories!

This is why ice at 0 ºC keeps stuff cold MUCH This is why ice at 0 ºC keeps stuff cold MUCH longer than water at 1 ºClonger than water at 1 ºC

This is why ice is used for coolingThis is why ice is used for coolingNOTNOT because ice is cold because ice is coldBut because it absorbs so much heat before it But because it absorbs so much heat before it will warm by one degreewill warm by one degree

29Heat Content of Waterat Various Temperatures

30Basic ChemistryBasic ChemistryProperties of Water:Properties of Water:Water as a SolventWater as a Solvent

Solutions consist of:Solutions consist of: A A solventsolvent (the most abundant part) and (the most abundant part) and A A solutesolute (less abundant part) that is dissolved in (less abundant part) that is dissolved in the solventthe solvent

Polar compounds readily dissolve; Polar compounds readily dissolve; hydrophilichydrophilicNonpolar compounds dissolve only slightly; Nonpolar compounds dissolve only slightly;

hydrophobichydrophobicIonic compounds dissociate in waterIonic compounds dissociate in water

NaNa++

­ Attracted to negative (O) end of HAttracted to negative (O) end of H22OO­ Each NaEach Na++ completely surrounded by H completely surrounded by H22OO

ClCl--

­ Attracted to positive (HAttracted to positive (H22) end of H) end of H22OO­ Each ClEach Cl-- completely surrounded by H completely surrounded by H22OO

31Basic ChemistryBasic ChemistryProperties of Water:Properties of Water:Uniqueness of IceUniqueness of Ice

Frozen water less dense than liquid waterFrozen water less dense than liquid water

Otherwise, oceans and deep lakes would fill Otherwise, oceans and deep lakes would fill with ice from the bottom upwith ice from the bottom up

Ice acts as an insulator on top of a frozen Ice acts as an insulator on top of a frozen body of waterbody of water

Melting ice draws heat from the environmentMelting ice draws heat from the environment

32Density of Waterat Various Temperatures

33A Pond in Winter

34Basic ChemistryBasic ChemistryProperties of Water:Properties of Water:Cohesion & AdhesionCohesion & Adhesion

CohesionCohesion – Hydrogen bonds hold water – Hydrogen bonds hold water molecules tightly togethermolecules tightly together

AdhesionAdhesion – Hydrogen bonds for between water – Hydrogen bonds for between water and other polar materialsand other polar materials

Allows water be drawn many meters up a tree in a Allows water be drawn many meters up a tree in a tubular vesseltubular vessel

High High Surface TensionSurface Tension Water molecules at surface hold more tightly than Water molecules at surface hold more tightly than below surfacebelow surface

Amounts to an invisible “skin” on water surfaceAmounts to an invisible “skin” on water surface Allows small nonpolar objects (like water strider) Allows small nonpolar objects (like water strider) to sit on top of waterto sit on top of water

35Water as a Transport Medium

36Basic ChemistryBasic ChemistrypH of Water:pH of Water:AcidsAcids

AcidsAcids

Dissociate in water and release Dissociate in water and release hydrogen ions (Hhydrogen ions (H++))

Sour to tasteSour to taste

Hydrochloric acid (stomach acid) is a Hydrochloric acid (stomach acid) is a gas with symbol HClgas with symbol HCl

­ In water, it dissociates into HIn water, it dissociates into H++ and Cl and Cl--

­Dissociation of HCl is almost total, therefore Dissociation of HCl is almost total, therefore it is a strong acidit is a strong acid

37Basic ChemistryBasic ChemistrypH of Water:pH of Water:BasesBases

BasesBases::

Either take up hydrogen ions (HEither take up hydrogen ions (H++) or ) or release hydroxide ions (OHrelease hydroxide ions (OH--))

Bitter to tasteBitter to taste

Sodium hydroxide (drain cleaner) is a Sodium hydroxide (drain cleaner) is a solid with symbol NaOHsolid with symbol NaOH

­ In water, it dissociates into NaIn water, it dissociates into Na++ and OH and OH--

­Dissociation of NaOH is almost total, Dissociation of NaOH is almost total, therefore it is a strong basetherefore it is a strong base

38Basic ChemistryBasic Chemistry

pH ScalepH Scale

pH scale used to indicate acidity and alkalinity pH scale used to indicate acidity and alkalinity of a solution.of a solution.Values range from 0-14Values range from 0-14­ 0 to <7 = Acidic0 to <7 = Acidic­ 7 = Neutral7 = Neutral­ >7 to 14 = Basic (or alkaline)>7 to 14 = Basic (or alkaline)

Logarithmic ScaleLogarithmic Scale­ Each unit change in pH represents a change of Each unit change in pH represents a change of 10X10X­ pH of 4 is 10X as acidic as pH of 5pH of 4 is 10X as acidic as pH of 5­ pH of 10 is 100X more basic than pH of 8pH of 10 is 100X more basic than pH of 8

39The pH Scale

40Basic ChemistryBasic Chemistry

Buffers and pHBuffers and pH

When HWhen H++ is added to pure water at pH 7, pH is added to pure water at pH 7, pH goes down and water becomes acidicgoes down and water becomes acidic

When OHWhen OH-- is added to pure water at pH 7, pH is added to pure water at pH 7, pH goes up and water becomes alkalinegoes up and water becomes alkaline

BuffersBuffers are solutes in water that resist change are solutes in water that resist change in pHin pH

When HWhen H++ is added, buffer may absorb, or is added, buffer may absorb, or counter by adding OHcounter by adding OH--

When OHWhen OH-- is added, buffer may absorb, or is added, buffer may absorb, or counter by adding Hcounter by adding H++

41Basic ChemistryBasic Chemistry

Buffers in BiologyBuffers in Biology

Health of organisms requires maintaining pH Health of organisms requires maintaining pH of body fluids within narrow limitsof body fluids within narrow limits

Human blood normally 7.4 (slightly alkaline)Human blood normally 7.4 (slightly alkaline)

Many foods and metabolic processes add or Many foods and metabolic processes add or subtract Hsubtract H+ + oror OHOH-- ions ions

­ Reducing blood pH to 7.0 results in acidosisReducing blood pH to 7.0 results in acidosis

­ Increasing blood pH to 7.8 results in alkalosisIncreasing blood pH to 7.8 results in alkalosis

­ Both life threatening situationsBoth life threatening situations

Bicarbonate ion (Bicarbonate ion (--HCOHCO33) in blood buffers pH to ) in blood buffers pH to 7.47.4