Water (HWater (H22O)O) 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

Take Home MessageTake Home Message

Water is unique among all liquids and the Water is unique among all liquids and the uniqueness plays a major role in life on uniqueness plays a major role in life on Earth and elsewhere in the solar systemEarth and elsewhere in the solar system

Water’s unusual and unique properties give Water’s unusual and unique properties give it a place “all its own” among compounds it a place “all its own” among compounds and moleculesand molecules

Water solutions and pH are critical concepts Water solutions and pH are critical concepts in chemistry and biologyin chemistry and biology

Emergent properties of HEmergent properties of H22O are a special O are a special case study of the significance of hierarchy case study of the significance of hierarchy theorytheory

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

SystemsSystems 25 of 92 natural elements are known 25 of 92 natural elements are known

to be essential to life on Earthto be essential to 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)

Compare to solar abundance and Compare to solar abundance and discuss relative to origin/evolution of discuss relative to origin/evolution of lifelife

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 is the most abundant Hydrogen is the most abundant element in universeelement in universe

Oxygen is the 3Oxygen is the 3rdrd most abundant most abundant elementelement

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 billions years of life in water aloneFirst 3 billions 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 Hof H22OO Exquisite properties of HExquisite properties of H22O arise from O arise from

chemical attractions among molecules chemical attractions among molecules because Hbecause H22O is a polar moleculeO is a polar 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 to Water in a liquid state is not too cold to

slow reactions and not too hot to break slow reactions and not too hot to break bondsbonds

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 a liquid (it floats)than a liquid (it floats)

Mechanism Mechanism HH22O expands when it solidifiesO expands when it solidifies 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: FreezingFreezing

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 (hydronium ion)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)…pH scale molar concentration)…pH scale Statistically very rare BUT exceedingly important Statistically very rare BUT exceedingly important

in chemistry of life (e.g., proteins, macromolecules)in chemistry of life (e.g., proteins, macromolecules) HH++ and OH and OH-- are very reactive and affect much are very reactive and affect much

of the chemistry of living systems (e.g., of the chemistry of living systems (e.g., membranes, metabolism)membranes, metabolism)

Water and pH Water and pH

Water and SolutionsWater and Solutions

Solutions: mixture of ions or Solutions: mixture of ions or molecules of 2 or more substancesmolecules of 2 or more substances Air as a mixture (OAir as a mixture (O22 in N in N22)) Tea as a mixture (aqueous if water))Tea as a mixture (aqueous if water)) Coffee as a mixture (aqueous)Coffee as a mixture (aqueous)

Solvent (majority) and solute Solvent (majority) and solute (minority)(minority)

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)

Water and Solutions: Water and Solutions: ConcentrationsConcentrations

MolesMoles Little furry critters with no eyes that live in tunnels Little furry critters with no eyes that live in tunnels

in the ground; 3 moles per acre is a 1 molar solutionin the ground; 3 moles per acre is a 1 molar solution Moles to a chemist are not furry animalsMoles to a chemist are not furry animals

1 mole is 1 gram molecular weight of a substance 1 mole is 1 gram molecular weight of a substance (atom, molecule), and it (atom, molecule), and it alwaysalways contains the exact contains the exact same number of atoms or moleculessame number of atoms or molecules

6.02 x 106.02 x 102323 atoms – Avogadro’s Number (not atoms – Avogadro’s Number (not avocado)avocado)

1 mole of C is 12 grams and it contains 6.02 x 101 mole of C is 12 grams and it contains 6.02 x 102323 atomsatoms

1 mole of Na is 23 grams and it contains 6.02 x 101 mole of Na is 23 grams and it contains 6.02 x 102323 atoms atoms

1 mole of H1 mole of H22O is 18 grams and it contains 6.02 x O is 18 grams and it contains 6.02 x 10102323 molecules of H molecules of H2200

Very precise way of measuring concentrationVery precise way of measuring concentration

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 B Substance A has a pH of 2 and Substance B has a pH of 3. This means that ____.has a pH of 3. This means that ____.A.A. Substance A is more basic than Substance A is more basic than Substance BSubstance BB.B. Substance B is more acidic than Substance B is more acidic than Substance ASubstance AC.C. Substance A is 10 times more acidic Substance A is 10 times more acidic than substance Bthan substance BD. Substance B is 10 times more acidic than D. Substance B is 10 times more acidic than substance Asubstance A

QuestionsQuestions

A deep lake in Minnesota is covered with ice. A deep lake in Minnesota is covered with ice. What is the water temperature at the bottom of What is the water temperature at the bottom of the lake?the lake?

In the summer in Virginia, pond water In the summer in Virginia, pond water temperature is very warm (~30 temperature is very warm (~30 00C). In the fall, C). In the fall, the drop in night time air temperature results the drop in night time air temperature results in surface water temperature falling (e.g., 20 in surface water temperature falling (e.g., 20 00C). What would you expect to happen in small C). What would you expect to happen in small ponds as the surface water temperature is ponds as the surface water temperature is cooler than the water temperature at the cooler than the water temperature at the bottom of the pond (~30 bottom of the pond (~30 00C)?C)?

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?

Take Home MessageTake Home Message

Water is unique among all liquids and the Water is unique among all liquids and the uniqueness plays a major role in life on uniqueness plays a major role in life on Earth and elsewhere in the solar systemEarth and elsewhere in the solar system

Water’s unusual and unique properties gives Water’s unusual and unique properties gives it a place “all its own” among compounds it a place “all its own” among compounds and moleculesand molecules

Water solutions and pH are critical concepts Water solutions and pH are critical concepts in chemistry and biologyin chemistry and biology

Emergent properties of HEmergent properties of H22O are a special O are a special case study of the significance of hierarchy case study of the significance of hierarchy theory in the natural sciencestheory in the natural sciences