7/29/2019 Water and Properties

1/15

13

GENERALCHEMIST

RY

Water and Properties

right The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

7/29/2019 Water and Properties

2/15

1. gas - particles widely separated,no definite shape or volume solid

2. liquid - particles closer together,definite volume but no definiteshape

3. solid - particles are very closetogether, define shape and definitevolume

1

.2Matterand

Properties

Three States of Matter

7/29/2019 Water and Properties

3/15

Three States of Water

(a) Solid (b) Liquid (c)Gas

7/29/2019 Water and Properties

4/15

Comparison of the Three PhysicalStates

1

.2Matterand

Properties

7/29/2019 Water and Properties

5/15

Polarity of Water

In a water molecule two hydrogen atomsform single polar covalent bonds with anoxygen atom. Gives water more structurethan other liquids

Because oxygen is more electronegative, the

region around oxygen has a partial negativecharge.

The region near the two hydrogen atoms has apartial positive charge.

A water molecule is a polar molecule with

opposite ends of the molecule withopposite charges.

7/29/2019 Water and Properties

6/15

Water has a variety of unusualproperties because of attractions

between these polar molecules.The slightly negative regions of one

molecule are attracted to the slightly

positive regions of nearby molecules,forming a hydrogen bond.

Each water moleculecan form hydrogen

bonds with up tofour neighbors.

Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 3.1

7/29/2019 Water and Properties

7/15

HYDROGEN BONDS Hold water molecules

together Each water molecule

can form a maximumof 4 hydrogen bonds

The hydrogen bondsjoining watermolecules are weak,about 1/20th as strongas covalent bonds.

They form, break, andreform with greatfrequency

Extraordinary Propertiesthat are a result ofhydrogen bonds.

Cohesive behavior

Resists changes intemperature

High heat of vaporization

Expands when it freezes

Versatile solvent

7/29/2019 Water and Properties

8/15

Properties of Water

Polar molecule

Cohesion and

adhesion High specific heat

Density greatest

at 4oC Universal solvent

of life

7/29/2019 Water and Properties

9/15

Organisms Depend onCohesion

Cohesion is responsible forthe transport of the watercolumn in plants

Cohesion among watermolecules plays a key role inthe transport of water againstgravity in plants

Adhesion, clingingof one substance toanother, contributestoo, as water adheresto the wall of the

vessels.

Hydrogen bonds hold the

substance together, aphenomenon called cohesion

7/29/2019 Water and Properties

10/15

Surface tension, a measure of theforce necessary to stretch or break

the surface of a liquid, is related tocohesion.

Water has a greater surface tension than

most other liquids because hydrogenbonds among surface water moleculesresist stretching or breaking the surface.

Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 3.3

7/29/2019 Water and Properties

11/15

Moderates Temperatures onEarth

Celsius Scale at Sea Level

100oC Water boils

37oC Human body

temperature

25oC Room temperature

0oC Water freezes

Water stabilizes air temperatures by absorbing heat fromwarmer air and releasing heat to cooler air.

Water can absorb or release relatively large amounts of heatwith only a slight change in its own temperature.

7/29/2019 Water and Properties

12/15

Three-fourths of the earthis covered by water. Thewater serves as a largeheat sink responsible for:

1. Prevention oftemperature fluctuations

that are outside therange suitable for life.

2. Coastal areas having amild climate

3. A stable marine

Specific Heat is the amount of heat that mustbe absorbed or lost for one gram of a

substance to change its temperature by 1oC.

7/29/2019 Water and Properties

13/15

Evaporative Cooling

The cooling of a surface occurswhen the liquid evaporates

This is responsible for:

Moderating earths climate

Stabilizes temperature in aquaticecosystems

Preventing organisms fromoverheating

7/29/2019 Water and Properties

14/15

Density of Water Most dense at 4oC

Contracts until 4oC

Expands from 4oC to 0oC

7/29/2019 Water and Properties

15/15

Most biochemical reactions involve solutesdissolved in water.

There are two importantquantitative proprieties of

aqueous solutions.

1. Concentration

2. pH