Biology Properties of Water. Matter consists of chemical elements in pure form and in combinations called compounds Organisms are composed of matter Matter.

Biology

Properties of Water

Matter consists of chemical elements in pure form and in combinations called compounds

• Organisms are composed of matter• Matter is anything that takes up space and has

mass

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Matter is made up of elements An element is a substance that cannot be broken down to other substances by chemical reactionsA compound is a substance consisting of two or more elements in a fixed ratioA compound has characteristics different from those of its elements

Table 2-1

Fig. 2-UN3

Nucleus

Protons (+ charge)determine element

Neutrons (no charge)determine isotope Atom

Electrons (– charge) form negative cloudand determinechemical behavior

Fig. 2-UN6

Ionic bond

Electrontransferforms ions

NaSodium atom

ClChlorine atom

Na+

Sodium ion(a cation)

Cl–

Chloride ion(an anion)

Fig. 2-9

Hydrogen

1H

Lithium

3LiBeryllium

4BeBoron

5BCarbon

6CNitrogen

7NOxygen

8O

Fluorine

9FNeon

10Ne

Helium

2HeAtomic number

Element symbol

Electron-distributiondiagram

Atomic mass

2He

4.00Firstshell

Secondshell

Thirdshell

Sodium

11NaMagnesium

12Mg

Aluminum

13AlSilicon

14SiPhosphorus

15PSulfur

16S

Chlorine

17ClArgon

18Ar

Electron-distributiondiagram

(a)

(b) Separate electronorbitals

Neon, with two filled shells (10 electrons)

First shell Second shell

1s orbital 2s orbital Three 2p orbitals

(c) Superimposed electronorbitals

1s, 2s, and 2p orbitals

x y

z

Fig. 2-10-4

Hydrogen Bonds

• A hydrogen bond forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom

• In living cells, the electronegative partners are usually oxygen or nitrogen atoms

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 2-16

+

+

+

+

+

Water (H2O)

Ammonia (NH3)

Hydrogen bond

Overview: The Molecule That Supports All of Life

• Water is the biological medium on Earth

• All living organisms require water more than any other substance

• Most cells are surrounded by water, and cells themselves are about 70–95% water

• The abundance of water is the main reason the Earth is habitable

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The polarity of water molecules results in hydrogen bonding

• The water molecule is a polar molecule: The opposite ends have opposite charges

• Polarity allows water molecules to form hydrogen bonds with each other


Fig. 3-2

Hydrogenbond

–H

+

H

O

——

——

+

+

+

–

–

–

Four emergent properties of water contribute to Earth’s fitness for life

• Four of water’s properties that facilitate an environment for life are:

– Cohesive behavior– Ability to moderate temperature– Expansion upon freezing– Versatility as a solvent


Cohesion

• Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion

• Cohesion helps the transport of water against gravity in plants

• Adhesion is an attraction between different substances, for example, between water and plant cell walls


Fig. 3-3

Water-conductingcells

Adhesion

Cohesion

150 µm

Directionof watermovement

• Surface tension is a measure of how hard it is to break the surface of a liquid

• Surface tension is related to cohesion


Fig. 3-4

Water’s High Specific Heat

• The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC

• The specific heat of water is 1 cal/g/ºC

• Water resists changing its temperature because of its high specific heat


Insulation of Bodies of Water by Floating Ice

• Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” making ice less dense

• Water reaches its greatest density at 4°C• If ice sank, all bodies of water would eventually

freeze solid, making life impossible on Earth


20

Heat Capacity• Water has a high heat capacity

Temperature = rate of vibration of molecules Apply heat to liquid

Molecules bounce faster Increases temperature

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

• Thermal inertia – resistance to temperature change More heat required to raise water one degree than most other liquids (1 calorie

per gram) Also, more heat is extracted/released when lowering water one degree than most

other liquids

21

Properties of Water:Heat of Vaporization

• High heat of vaporization

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

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

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

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

• This is why sweating (and panting) cools

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

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

22

Evaporative Cooling

of Animals

23

Heat of Fusion

• Heat of fusion (melting)

– To raise ice from -2 to -1 ºC; ~1 calorie

– To raise water from -1 to 0 ºC; ~1 calorie

– To raise water from 0 to 1 ºC; ~80 calories!

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

• This is why ice is used for cooling

– NOT because ice is cold

– But because it absorbs so much heat before it will warm by one degree

24

Heat Content of Water

at Various Temperatures

25

Properties of Water:Uniqueness of Ice

• Frozen water less dense than liquid water

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

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

Melting ice draws heat from the environment

26

A Pond in Winter

27

Density of Waterat Various Temperatures

Fig. 3-6a

Hydrogenbond

Liquid waterHydrogen bonds break and re-form

IceHydrogen bonds are stable

Hydrophilic and Hydrophobic Substances

• A hydrophilic substance is one that has an affinity for water

• A hydrophobic substance is one that does not have an affinity for water

• Oil molecules are hydrophobic because they have relatively nonpolar bonds

• A colloid is a stable suspension of fine particles in a liquid


Basic ChemistryBasic Chemistry 30Properties 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

Biology Properties of Water. Matter consists of chemical elements in pure form and in combinations called compounds Organisms are composed of matter Matter.

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