REVIEW: Water Structure

• A water molecule consists of 2 hydrogen and

1 oxygen atom, hence…H2O.

• Electrons are shared through polar covalent

bonding between the atoms.

REVIEW:

Water molecules can form hydrogen bonds

• Partly positive hydrogen atoms of one water molecule are attracted to the partially negative oxygen atom of another water molecule

• The bonds are made and broken quickly as the molecules move, however the large numbers of bonds contribute to the stability of water

Properties of Water

#1

Water Forms an Unusual Solid: Ice

• Most substances become denser when

they solidify from a liquid

• Ice is unusual because it is less dense

than liquid water

Water Forms an Unusual Solid: Ice

LIQUID: Water

molecules are able

to pack tightly and

“roll” around each

other by creating

hydrogen bonds

that form and break

quickly

SOLID: Water

molecules spread

apart slightly during

the freezing process

as the hydrogen

bonds “lock” into place

Water Forms an Unusual Solid: Ice

• As a result, ice floats in liquid water

• Ponds and lakes freeze from the top

down and never freeze completely to the

bottom

– Many plants and fish therefore are not

frozen

#2

Water Dissolves Many Molecules

making it an excellent “SOLVENT”

• Water is the solvent of life

• Water will dissolve:

– Other molecules that have polar covalent

bonds molecules (i.e. amino acids or glucose)

– Ionic compounds (i.e. NaCl, table salt)

Water Interacts with Many Molecules

• Molecules that will dissolve in water are

hydrophilic

Notice that the

slightly positive

part of water

(the H) is

attracted to the

negative

charged

chlorine ion

Notice that the

slightly negative

part of water

(the O) is

attracted to the

positive charged

sodium ion

Water Interacts with Many Molecules

• Water-insoluble molecules

are hydrophobic

– Water molecules are not

attracted to uncharged and

nonpolar molecules like fats

and oil

Water Molecules Tend to Stick Together

• Hydrogen bonding

between water

molecules produces

high cohesion

#3

Water cohesion

explains how

water

molecules can

form a chain in

delivering

water from the

roots to the top

of a tree

That’s

a big

tree!

That’s a

long chain

of water!

Notice the O

(slightly -) is

attracted to the H

(slightly +) of A

DIFFERENT

water molecule

The water is not falling off

the penny because it is

sticking to other water

molecules = COHESION

• Cohesion of water molecules along a

surface produces surface tension

Fishing spiders

and water striders

rely on surface

tension to move

across the

surface of ponds

Surface tension results from the great attraction of water molecules to each

other (due to cohesion). The net effect is an inward force at its surface that

causes water to behave as if its surface were covered with a stretched elastic

membrane. Because of the relatively high attraction of water molecules for

each other, water has a high surface tension compared to that of most other

liquids.

Adhesion • Water molecules sticking to

other surfaces

• The other surfaces are polar

or ionic

#4

Adhesion of

the water to

the spider silk

Adhesion of water

molecules to the

sides of the tube

Cohesion of water to other

water molecules

• Adhesion helps water climb up the thin

tubes of plants to the leaves

• Click link for an overview of “capillary

action”

Water Stabilizes Temperature

• Compared to other molecules, it takes a lot

of energy to change the temperature of

water

– It requires 1 calorie of energy to raise the

temperature of 1g of water 1oC (the specific

heat of water)

• So water heats up or cools down very slowly

– This provides for a stable internal environment

and habitat

#5

Water Stabilizes Temperature

• Because the human body is mostly water, a

sunbather can absorb a lot of heat energy

without sending her/his body temperature

soaring

Water Stabilizes Temperature

• Water requires a lot of energy to turn from

liquid into a gas (heat of vaporization)

– Water requires a high input of energy to break

the hydrogen bonds to turn it from a liquid to a

gas.

– Evaporating water uses up heat from its

surroundings, cooling the nearby environment

(as occurs during sweating)

– Here’s a good link to explain evaporative

cooling

#6

Heat of vaporization

Organisms rely on heat of vaporization to remove body heat

Evaporative cooling

Transparency

Because water is

transparent, light

penetrates tissue and

aquatic environments,

important for

photosynthesis.