Water (HWater (H22O)O)04 October 200504 October 2005

Why water exists and why is it Why water exists and why is it importantimportant

Water’s unusual propertiesWater’s unusual properties Hydrogen bonding and polarityHydrogen bonding and polarity Liquid stateLiquid state CohesionCohesion SolventSolvent

Water and solutionsWater and solutions Hierarchy theory and the emergent Hierarchy theory and the emergent

properties of waterproperties of water

Elements of the Solar Elements of the Solar System: Role in Living System: Role in Living

SystemsSystems

25 of 92 natural elements essential 25 of 92 natural elements essential to life on Earthto life on Earth

Four of the above make up 96%Four of the above make up 96% Carbon (C), Carbon (C), Oxygen (O),Oxygen (O), HydrogenHydrogen

(H)(H) and Nitrogen (N) and Nitrogen (N) Solar abundance and importance Solar abundance and importance

relative to origin/evolution of liferelative to origin/evolution of life

Elements of the Elements of the Periodic TablePeriodic Table

Relative Abundance of Elements in the Sun

0

2

4

6

8

10

12

0 5 10 15 20 25 30 35 40 45

Atomic Number

Log

of R

elat

ive

Abu

ndan

ce (S

i)

H

He

Li

Be B

C

C

N

O

Fe

Ne

Na

Mg

Al

Si

P

S

Cl

Ar

K

Ca

Fe

Water and Its Water and Its Properties: Properties:

CompositionComposition

Elemental composition of HElemental composition of H22OO Hydrogen: most abundant element in Hydrogen: most abundant element in

universeuniverse Oxygen: 3Oxygen: 3rdrd most abundant element most abundant element

Hypothesis: HHypothesis: H22O is common O is common throughout the universethroughout the universe

Liquid Solution for Liquid Solution for Living SystemsLiving Systems

IntroductionIntroduction Life on Earth in water ~4 billion years Life on Earth in water ~4 billion years

agoago First 3 billion years of life in water aloneFirst 3 billion years of life in water alone All life tied to watery medium (plants, All life tied to watery medium (plants,

animals and microbes)animals and microbes) SimplicitySimplicity and and complexitycomplexity of the of the

nature of the water moleculenature of the water molecule Deceptively Deceptively simplesimple in structure in structure ExquisiteExquisite in function in function

Water and Its Properties: Water and Its Properties: PolarityPolarity

Composition and structure: a polar moleculeComposition and structure: a polar molecule

FeaturesFeatures Attraction is electricalAttraction is electrical Hydrogen bonding among Hydrogen bonding among two or more moleculestwo or more molecules of of

HH22OO Exquisite properties of HExquisite properties of H22O: chemical O: chemical

attractions among molecules because Hattractions among molecules because H22O is a O is a polar moleculepolar molecule

Water and Its Properties: Water and Its Properties: PolarityPolarity

Water and Its Properties: Water and Its Properties: Phase DiagramPhase Diagram

Water and Its Properties: Water and Its Properties: Liquid StateLiquid State

Water is liquid over broad range of Water is liquid over broad range of temperaturestemperatures

00ooC to 100C to 100ooCC

ComComparisonparison with other compounds with other compounds

CompoundCompound Chemical FormulaChemical Formula FreezeFreeze VaporVapor RangeRange ((ooC) (C) (ooC) (C) (ooC)C)

WaterWater H H22OO 0 0 100 100 100 100

AmmoniaAmmonia NH NH33 -78 -78 -33 -33 45 45

MethaneMethane CH CH44 -182 -182 -164 -164 18 18

Water and Its Water and Its Properties: Liquid StateProperties: Liquid State

Significance of broad range of Significance of broad range of temperatures for water to exist as a temperatures for water to exist as a liquidliquid Water in a liquid state is not too cold Water in a liquid state is not too cold

to slow reactions and not too hot to to slow reactions and not too hot to break bondsbreak bonds

Could life evolve in another phase Could life evolve in another phase (i.e., gas, solid)?(i.e., gas, solid)?

Water and Its Water and Its Properties: Cohesion of Properties: Cohesion of

MoleculesMolecules Cohesion: HCohesion: H22O molecules are “sticky”O molecules are “sticky” Each hydrogen bond last 1 x 10Each hydrogen bond last 1 x 10-12-12 seconds seconds Constant formation and breakage of Constant formation and breakage of

bonds: any moment, a substantial number bonds: any moment, a substantial number of Hof H22O molecules are bonded to its O molecules are bonded to its neighbors neighbors

Consequence: more structure than other Consequence: more structure than other liquidsliquids

Water and Its Properties: Water and Its Properties: FreezingFreezing

Water is unusual in that Water is unusual in that HH22O is less dense as a solid O is less dense as a solid than as a liquid (it floats)than as a liquid (it floats)

Mechanism Mechanism HH22O expands when it O expands when it

solidifiessolidifies Due to hydrogen bondingDue to hydrogen bonding

ConsequenceConsequence Ponds, lakes and ocean freeze Ponds, lakes and ocean freeze

from the top downfrom the top down Consequence for living Consequence for living

system?system?

Water and Its Properties: Water and Its Properties: Solvent of LifeSolvent of Life

Water is versatile solvent due to its polarity Water is versatile solvent due to its polarity and dissociationand dissociation

HH22O HO H++ + OH + OH--

HH22O + HO + H++ H H33OO++ (hydronium ion)(hydronium ion) In pure water, 1 molecule in every In pure water, 1 molecule in every 554 million554 million is is

dissociated (10dissociated (10-7-7 molar concentration)… molar concentration)…pH scalepH scale Statistically very rare BUT exceedingly important Statistically very rare BUT exceedingly important

in chemistry of lifein chemistry of life HH++ and OH and OH-- are very reactive and affect much are very reactive and affect much

of the chemistry of living systemsof the chemistry of living systems

Water and pH Water and pH

Water and Solutions: Water and Solutions: ConcentrationsConcentrations

Concentrations of solutes and solventsConcentrations of solutes and solvents Parts per million (ppm) or billion (ppb)Parts per million (ppm) or billion (ppb)

Atmosphere and carbon dioxide (370 ppm)Atmosphere and carbon dioxide (370 ppm) Percentage by massPercentage by mass

Salinity of ocean water - mass of salts in 1,000 Salinity of ocean water - mass of salts in 1,000 grams of water (35 g in 1000 g water)grams of water (35 g in 1000 g water)

Chemistry: molarity of solutionChemistry: molarity of solution # moles of solute dissolved in 1 liter of solvent # moles of solute dissolved in 1 liter of solvent

(H(H22O)O)

Hierarchy Theory and Hierarchy Theory and Emergent Properties of HEmergent Properties of H22OO

Principle of Principle of hierarchy theoryhierarchy theory Principle of Principle of emergent propertiesemergent properties Example of HExample of H22O in Periodic TableO in Periodic Table a prioria priori: combine one atom of O with two : combine one atom of O with two

atoms of Hatoms of H Emergent propertiesEmergent properties

LiquidLiquid Hydrogen bonding and polarityHydrogen bonding and polarity H+ and OH- in solutionH+ and OH- in solution SolventSolvent Range of temperature at which liquidRange of temperature at which liquid Three phases (gas, liquid and solid)Three phases (gas, liquid and solid)

QuestionQuestion

Substance A has a pH of 2 and Substance Substance A has a pH of 2 and Substance B has a pH of 3. This means that ____.B has a pH of 3. This means that ____.

A.A. Substance A is more basic than Substance A is more basic than Substance BSubstance B

B.B. Substance B is more acidic than Substance B is more acidic than Substance ASubstance A

C.C. Substance A is 10 times more acidic Substance A is 10 times more acidic than substance Bthan substance B

D. Substance B is 10 times more acidic D. Substance B is 10 times more acidic than substance Athan substance A

QuestionsQuestions

A deep lake in Virginia is covered with ice in A deep lake in Virginia is covered with ice in January. What is the water temperature at the January. What is the water temperature at the bottom of the lake relative to that of the surface bottom of the lake relative to that of the surface water?water?

QuestionQuestion

How does ocean water in proximity How does ocean water in proximity to continents affect the climate of to continents affect the climate of the adjoining land mass? Explain the adjoining land mass? Explain your analysis based on the physical your analysis based on the physical and chemical properties of water.and chemical properties of water.

QuestionQuestion

In the search for life on other In the search for life on other planets and in other solar systems, planets and in other solar systems, why is the presence and/or absence why is the presence and/or absence of water regarded as one of the of water regarded as one of the cardinal indicators of the possibility cardinal indicators of the possibility of life?of life?