Chapter 6:

Water and Ocean Structure

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Learning Goals:

Water and Ocean Structure

• The properties of water moderate Earth’s temperatures and

enable life on Earth.

• Water resists rising in temperature as it is heated. Water

gives off heat when it freezes, and it absorbs heat as it

thaws.

• Seawater is mostly water molecules but has dissolved

substances.

• The ocean is stratified by density.

Density is driven mainly by temperature and salinity.

• Light is extinguished easily as it passes through water.

Sound is not.2

Water has unique properties

that enable life on Earth.

1. It’s a good solvent.

2. Ice floats.

3. Water has a high heat capacity.

4. Water helps the metabolism of organisms.

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4

Atomic Structure• Atoms – building blocks

of all matter

• Subatomic particles

– Protons

– Neutrons

– Electrons

• Number of protons

distinguishes chemical

elements

5

105°

2 hydrogen

atoms...

share their electrons

with 1 oxygen

atom...

to form water molecule

held together by

covalent bonds...

and creates

negative &

positive ends.

Nucleus (+1 charge)

Electron

(–1 charge)

Structure of Water

Polar Covalent bonds

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Molecules

• Molecule

– Two or more atoms held together by shared

electrons

– Smallest form of a substance

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Water molecule

• Strong covalent bonds

between one hydrogen (H)

and two oxygen (O) atoms

• Both H atoms on same side

of O atom

– Bent molecule shape gives

water its unique properties

• Dipolar

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Hydrogen Bonding

• Polarity means small negative charge at O end

• Small positive charge at H end

• Attraction between positive and negative ends of water molecules to each other or other ions

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Hydrogen Bonding

• Hydrogen bonds are weaker than covalent

bonds but still strong enough to contribute

to

– Cohesion – molecules sticking together

– High water surface tension

– High solubility of chemical compounds in

water

– Unusual thermal properties of water

– Unusual density of water

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Water has unique properties

that enable life on Earth.

1. It’s a good solvent.

2. Ice floats.

3. Water has a high heat capacity.

4. Water helps the metabolism of organisms.

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Water as Solvent

• Water molecules stick

to other polar

molecules.

• Electrostatic attraction

produces ionic bond.

• Water can dissolve

almost anything –

universal solvent

PhET.colorado.edu

http://phet.colorado.edu/en/simulation/legacy/sugar-and-salt-solutions 12

Water has unique properties

that enable life on Earth.

1. It’s a good solvent.

2. Ice floats.

3. Water has a high heat capacity.

4. Water helps the metabolism of organisms.

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Why does ice float?

• Generally speaking, cold water is more

dense than warm water.

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Density

volume

mass

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Water’s Three States of Matter

volume

mass

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Hydrogen bonds cause density to

decrease once colder than 4°C.

If > 1 g/cm3 (pure water), object will sink.

If < 1 g/cm3, object will float.

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Water has unique properties

that enable life on Earth.

1. It’s a good solvent.

2. Ice floats.

3. Water has a high heat capacity.

4. Water helps the metabolism of organisms.

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Oceans can minimize temperature fluctuations.

37.8 deg N19

Water has high heat capacity;

which means it is harder to

change phase/temperature.

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Global Thermostatic Effects

• Marine effect

– Oceans moderate temperature changes from day to night and during different seasons

• Continental effect

– Land areas have greater range of temperatures from day to night and during different seasons

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Day and Night Temperature

Differences

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Atmospheric Heat Transport

Water moves heat between latitudes.23

Latent heat of fusion – heat needed to change from solid to liquid.

Latent heat of vaporization – heat needed to change from liquid to vapor.

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Water has unique properties

that enable life on Earth.

1. It’s a good solvent.

2. Ice floats.

3. Water has a high heat capacity.

4. Water helps the metabolism of organisms.

What percentage of human blood is water?

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Ocean water

• What affects the density of seawater?

1) Temperature

2) Salinity

3) Pressure (only at great depths)

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Salinity

• Expressed in parts

per thousand (ppt)

• Typical ocean

salinity is 35 ppt

(o/oo)

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In places with high

stratification, mixing

between layers difficult.

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Below sea surface, layers are stratified.

Surface zone (or mixed layer) – upper layer, waves

keep everything mixed.29

Surface zone depth varies from 0 to 3300 feet.

Thermocline – where temperature decreases rapidly.

Pycnocline – where density increases rapidly.

Deep Zone – little change in density (80% of ocean).30

Question

• What type of bond holds the 2 hydrogen

and 1 oxygen together to form water?

a) Hydrogen

b) Covalent

c) Ionic

d) Polar Covalent

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Question

• What type of bond holds the 2 hydrogen

and 1 oxygen together to form water?

a) Hydrogen

b) Covalent

c) Ionic

d) Polar Covalent

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Question

• When water vapor condenses to form

rain, what happens to the air around it?

a) It freezes

b) Its pressure lowers

c) It warms

d) It cools

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Question

• When water vapor condenses to form

rain, what happens to the air around it?

a) It freezes

b) Its pressure lowers

c) It warms

d) It cools

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Question

• The region below the sea surface where

salinity increases rapidly is called the

a) Halocline

b) Pycnocline

c) Thermocline

d) Salocline

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Question

• The region below the sea surface where

salinity increases rapidly is called the

a) Halocline

b) Pycnocline

c) Thermocline

d) Salocline

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Question

• Why do you add salt to ice to get your car unstuck from the ice?

a) Salt creates an exothermic reaction heating the ice

b) Salt raises the freezing point

c) Salt lowers the freezing point

d) Salt molecules move faster than water molecules thereby providing additional heat

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Question

• Why do you add salt to ice to get your car unstuck from the ice?

a) Salt creates an exothermic reaction heating the ice

b) Salt raises the freezing point

c) Salt lowers the freezing point

d) Salt molecules move faster than water molecules thereby providing additional heat

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Question

• Which of the following would lower the

salinity of saltwater near the surface?

a) Freezing of seawater into ice

b) More rainfall

c) More evaporation

d) Additional mixing from the deep zone

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Question

• Which of the following would lower the

salinity of saltwater near the surface?

a) Freezing of seawater into ice

b) More rainfall

c) More evaporation

d) Additional mixing from the deep zone

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