Professional Scientific Societies ES/RP 532 Applied ...Polarity (Polar Bonds) Owing to differences...

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ES/RP 532Applied Environmental Toxicology

Lecture 2Environmental Analytical Chemistry

Chemical Functional GroupsPhysicochemical Properties

Professional Scientific Societiesfor Toxicology

Society of Toxicology (SOT) http://www.toxicology.org/

Society of Environmental Toxicology &Chemistry (SETAC) http://www.setac.org/

Goal of EnvironmentalToxicology

Predict the effects or impact of chemicaltechnologies on organism (ecosystems)

Conceptual Frameworks for UnderstandingFate & Effect of Environmental

Contaminants Environmental Chemodynamics Toxicodynamics

The Logical Process forDetermining Likelihood of Effects Risk Assessment

Hazard Identification Dose-response characterization Exposure assessment Risk characterization

What Is Needed toEstimate (Guess) The Risk?

Risk Assessment

Toxicology Environmental Chemistry

No Observable Effect Level

Exposure Assessment

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“Residues”

Residues refer to chemicalcontaminants in the physicalenvironment and in biological tissues The constituents of chemical products (or

formulations) become residues when theyare dispersed into the environment

Residue Amount Expressed as a concentration

Unit of mass per volume or surface areaMilligrams per Liter (mg/L) (or per square meter)Micrograms per milliliter (µg/mL) (or per sq. cm)

A proportion1% (1 part per 100)0.0001% (1 part per million)

A molar quantityMoles/L (if in solution)

– One mole = the molecular weight of a substance in grams– 1 µmol = the molecular weight in micrograms

What Does It Mean?

Usual range of detections manyenvironmental contaminants rangesfrom ppt (parts per trillion) - ppb (partsper million) From the perspective of purity, that

translates to 99.9999999999% -- 99.9999999% I.e., if 1 ppb = 0.0000001%, then 100%

minus 0.0000001% yields 99.9999999%

99.4% Pure!!!!!!!!

1950 1960 1970 1980 1990 2000

GramsPerLiterg/L ???

100

10-3

10-6

10-9

10-12

10-15

ppthppm

ppbppt

ppq

Year

Analytical Technology Has Advanced FasterThan Biological Understanding

BBBB

B

B

B

B

B

0

5

10

15

20

25

30

35

40

45

0.001 0.01 0.1 1 10

Atrazine Reporting Limit (µg/L)

% Frequency

Frequency of Atrazine Detection in Shallow AquifersIncreases as Reporting Limit Decreases

Kolpin et al. JEQ 25 (1996)

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Pesticide Residues--Frequencies/Identities/Concentrations

Method Detection Limit Method Quantitation Limit Concentrations

means medians geometric mean percentiles

Relevant Questions General Chemistry Review

Emphasis on Functional Groups&

The Concept of Polarity

# of Electrons in Shella

Name Symbol AtomicNumber

AtomicMass

1(K)

2(L)

3(M)

4(N)

5(O)

NetCharge of

Kernel

No. ofCovalent

BondsHydrogen H 1 1.008 1 1+ 1Helium He 2 4.003 2 0

Carbon C 6 12.011 2 4 4+ 4Nitrogen N 7 14.007 2 5 5+ 3, (4)c

Oxygen O 8 15.999 2 6 6+ 2, (1)d

Fluorine F 9 18.998 2 7 7+ 1Neon Ne 10 20.180 2 8 0

Phosphorus P 15 30.974 2 8 5 5+ 3,5Sulfur S 16 32.060 2 8 6 6+ 2, 4, 6, (1)c

Chlorine Cl 17 35.453 2 8 7 7+ 1Argon Ar 18 39.948 2 8 8 0

Bromine Br 35 79.904 2 8 18 7 7+ 1Krypton Kr 36 83.800 2 8 18 8 0

Iodine I 53 126.905 2 8 18 18 7 7+ 1Xenon Xe 54 131.290 2 8 18 18 8 0

Table 2. Electronegativities of Atoms (the greater the number the greater the EN)Charge of kernel1 +1 +4 +5 +6 +7

H2.2

Increasing Size of kernell

C2.5

N3.0

O3.5

F4.0

l

P2.2

S2.5

Cl3.0

l

Br2.8

l

I2.5

l

1 The kernel refers to the nucleus and the inner filled electron shells

Electronegativity (EN)

EN increases left to right across columns;EN decreases top to bottom across rows

e- e-

e-C

e-e-

e-

e-Ce-

Covalent Bonds

Formed between atoms by sharingelectrons

e-

e-e-

e-

e-

e-

e-

e-

e-

e-

C C

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Polarity (Polar Bonds) Owing to differences in electronegativity,

sharing of electrons in the bondingorbitals may be unequal, i.e., towardone atom or the other

Thus, positive (electron deficient) andnegative (electron rich) poles are set upbetween atoms in a molecule

C Oδ+ δ−

Ionic Bonding When atoms of very large differences in EN

bond, such as between column 7 andcolumn 1 or 2 elements, then the electronsmay be transferred from the atoms of lowestelectronegativity to the atoms of highestelectronegativity

Thus, the atoms of highest EN would have a“permanent” negative charge

The atoms of lowest EN would have a“permanent” positive charge

Na+ Cl-

O Hδ+δ−

Nδ−

Hydrogen Bonding When hydrogen (H) is bonded to O or N,

which are more electronegative, then therelatively positive H can be attracted to anelectronegative atom on nearby molecules Especially if the more EN atom has an unbonded

pair of electrons Forms a hydrogen bond; not as strong as

covalent or ionic bond, but it can form stablemolecular interactions

Geometry (Bond Angles) Atoms within molecules actually exist in

definite geometric spatial relationshipsto one another that are characteristic ofthe type of bond For ex., carbon atoms have four valence

electrons, each oriented toward the cornerof a tetrahedron;

C

N

Nitrogen often uses three valence electrons (with anunpaired electron available for bonding an electrondeficient species like H); its spatial geometry tends toby trigonal

Geometry (Bond Angles) Double bonds will make a molecule

more rigid, giving the atoms lessdegrees of freedom to flop around androtate about each other

C C

Geometry (Bond Angles) Aromatic structures (alternating double bonds

in ringed systems) tend to be planar (i.e., lessfree rotation of the carbon atoms) Characterized by delocalized ‘pi’ electrons that

can impart some electronegative character Aromatic structures also are more stable than

non-cyclic structures

Note that double bonds in linear structures also havedelocalized ‘pi’ bonds

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Dipole Moment

The overall polarity of a molecule depends onboth the presence of polar bonds and on thegeometry of the molecule Planar, trigonal, tetrahedral

The the determinant of overall polarity is thevector sum of the individual polar bonds (i.e.,dipole moment of individual bonds), which iscalled the molecular dipole moment

CH

HH Cl

C OO

Dipole Moment (p) = 0

http://www.chem.tamu.edu/organic/Spring99/dipolemoments.html

p = 6.2 X 10-30 C.mor

1.84 D (debyes)

Intermolecular Forces

Attraction betweenmolecules due toinstantaneous dipolemoments



Substance Molecular Mass Dipole Momentµ (D)

B oiling Point°K

propane, CH3CH2CH3 44 0.1 231dimethyl ether, CH3OCH3 46 1.3 248methyl chloride, CH3Cl 50 2.0 249acetaldehyde, CH3CHO 44 2.7 294acetonitrile, CH3CN 41 3.9 355

The various intermolecular interactions canexplain various physicochemical properties

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R1 NR3

R2amino (primary amine, R2 = R3 = H secondary amine, R3 = H tertiary amine, R1, R2, R3 = C

aniline if R =

-C-C-C-C-

R-OH

R-SH

R1-O-R2

R1-S-R2

alkyl (can be denoted by R)

hydroxy (alcohol, if phenol then R = )

mercapto (thiol, mercaptan)

ether

sulfide (thioether)

Functional Groups impart characteristics upon molecules thatare important in intermolecular interactions and reactivity

R1 C R2

O

carbonyl (ketone, aldehyde when R 2 = H

R C OH

O

carboxy (carboxylic acid)

R1 C O R2

O

ester (carboxylic acid ester)

R1 C S R2

O

thioester

R1 C N

OR2

R3

amide

R C N cyano (nitrile)

phosphate ester (if X = O); thiophosphate ester (if X = S)

nitro

R N O

R NO

O

P O R3R2 O

R1 O X

nitroso

H3C CH2 CH3

Saturation

CH3H3C CH2

Unsaturation

ortho meta para

1 2345

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anthracene

Vapor Pressure The pressure of the vapor of a

compound at equilibrium with its purestate Think of VP as the escaping tendency of

the molecules of a pure substance fromitself

Compound to compound variationsarise as a result of intermolecular forces

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Pressure Gauge

Solution of benzene

Vapor PressureRanges forSeveral Groups ofContaminants

Schwarzenbach et al. 1993

Smaller moleculesin homologousseries tend to havehigher VPs


Vapor pressure tends todecrease with increasecarbon chain length

Vapor pressure isdependent onambient temperature


Water Solubility

The amount of a substance thatdissolves in a given quantity of water ata given temperature to form a saturatedsolution Think of it as the escaping tendency of

molecules from one another when placedin water

Limitations to Water Solubility Regular, highly ordered structure of water

Results from high degree of hydrogen bonding Cause of very high surface tension for such a

small moleculeSurface tension is the intermolecular, cohesive

attraction between like molecules of a liquidthat cause it to minimize its surface area

Causes the high boiling point of water A solute dissolving in water has to disrupt the

orderly structure of water (with consequentenergy costs) Think of it as punching a hole in the water

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O

H H HH

O

HH

O

HH

O

HH

O

HH

O

HH

O

HH

O

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/diph2o.html#c3

Highly ordered structure ofwater due to extensivehydrogen bondingbetween molecules

Imbalance of intermolecular forces at“edge” of water tends to draw outerlayer of molecules into the interior,thereby reducing the surface area.

The water molecules inthe interior of the liquidare attracted equally inall directions.

Surface tension is the measure of inward forces at the surfacethat must be overcome to expand the surface area of the liquid.

Solutes (for ex., any contaminantin water) disrupt the waterstructure. That is, theintermolecular forces betweenwater molecules are disrupted.

If contaminant has functional groupsthat can hydrogen bond with water,then the water structure is disruptedless and more of the contaminant candissolve in the water (comparativelyless free energy in the system) Schwarzenbach et al. 1993

Change in HeatContent


Facilitation & Limitationsof Water Solubility

If a dissolving molecule has functional groupsthat allow hydrogen bonding, then theregularity of the water structure is disruptedless than if the molecule lacked the capabilityof hydrogen bonding

If no polar functional groups, than moreenergy must be expended to disrupt thewater structure Thus, entropy would necessarily be higher, and

consequently, WS would be less

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Examples of WaterSolubility Rangesfor DifferentGroups ofContaminants


Distilled Water vs. SeawaterCompound Solubility, distilled H2O (ppm) Solubility, seawater (ppm)toluene 506.7± 6.1 418.5 ± 5.0acenaphthene 2.42 ± 0.02 1.84 ± 0.04pyrene 0.13 ± 0.01 0.09 ± 0.01

Effect of Temperature on Solubilitylog solubility (ppb)

Compound Molar Volume (mL) 15°C 20°C 25°Ctoluene 109 5.61 5.61 5.62acenaphthene 150 2.33 2.74 3.26pyrene 172 1.75 1.85 1.95

Rossi & Thomas, Environ. Sci. Technol. (1981), p. 715

Other dissolved substances can affect watersolubility of a compound. Solubility can befacilitated by the co-dissolved solvent re-orientingthe water structure so that the compound “fits” intothe water structure in a more thermodynamicallyfavorable manner.




Recall that solution pH is the negative logarithm of the hydrogen ion [H+]concentration. H20 <====> H+ + OH-

H+ + H2O <===> H3O+, and K = 1 at equilibrium; Kw = [H+] x [OH-] = 1 x 10-14 M (the ion product constant for water)

For any acid (or base):HA + H2O <====> H3O+ + A-

Ka = [H + ][A − ]

[HA]= acidity dissociation constant

pH=pKa + log[A− ][HA]

pKa can be thought of as a measure of the tendency of an acid to dissociate (i.e.,deprotonate); by the same analogy, pKb is the tendency of a base to protonate

pKa (and pKb) can be thought of as the tendency of an acid to dissociateor a bases to accept a proton (H+). When pH = pKa, the concentration ofA- (the salt form) and HA are equal.

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Note that protondissociation wouldonly occur atunrealistically highpHs.


pH influences the relative abundance of the species of an organic acid,especially those with more than one acid or base functional group.


Molar Volume

The volume occupied by one mole of asubstance in the gas phase. Regarding liquids and solids, the molar

volume is the volume occupied by a moleof substance in aqueous solution

In a very dilute solution, the molar volumeapproaches that of water (18 x 10-6 m3/mol)

Correlated with WS and VP


As molar volume increases, the entropy for dissolutionalso increases because more energy has to be put intothe system to reorganize the water.


Professional Scientific Societies ES/RP 532 Applied ...Polarity (Polar Bonds) Owing to differences...

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