chapter 6 water. © 2006 brooks/cole, a division of thomson learning, inc. the water molecule is...

Chapter 6 Water

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

The Water Molecule Is Held Together by Chemical Bonds

A water molecule is composed of two hydrogen atoms and one oxygen atom. Water is a polar molecule, having a positive and a negative side.

A molecule is a group of atoms held together by chemical bonds.

Fig. 6-1, p. 155

Two hydrogen atoms...

share their electrons with one oxygen atom...

to form a water molecule held together by covalent bonds...

which acts as if it has negative and positive ends.

Nucleus (+1 unit of charge)

Electron (–1 unit of charge)

Stepped Art

2 – 105°


Water’s Chemical Bonds

Cohesion – the ability of water molecules to stick to each other, creating surface tension.

Adhesion – the tendency of water molecules to stick to other substances


Heat Capacity

Water has a very high heat capacity, which means it resists changing temperature when heat is added or removed.


Water Becomes Less Dense When It Freezes

Because molecules of liquid water are packed less efficiently, ice is less dense than liquid water and floats.


Water Removes Heat from Surfaces As It Evaporates

This cools the air and affects global temperatures.


Coastal Communities have milder temperatures than inland communities.


Ocean-Surface Conditions Depend on Latitude, Temperature, and Salinity

Average surface temperature and salinity for the world ocean. As you would expect, temperatures are lowest in the polar regions and highest near the equator. Heavy rainfall in the equatorial regions “freshens” the ocean near the equator, whereas hot and dry conditions near the tropic lines (Tropic of Capricorn and Tropic of Cancer) result in higher surface salinity in those areas.


Sea-surface average salinities in parts per thousand (‰).


The Ocean Is Stratified into Three Density Zones by Temperature

and Salinity

Surface zone – the upper layer of the ocean, containing the least dense water. The surface zone is only about 2% of total ocean volume.


Pycnocline – a zone in which density increases with depth, containing about 18% of all ocean water

Deep zone – contains about 80% of all ocean water. There is little change in density throughout this layer.


Fig. 6-18b, p. 169

Pycnocline is also a Thermocline

0 Surface zone

Pycnocline 3,281

16,562

9,843

Dep

th (

ft)

2

Dep

th (

km)

3

Deep zone

13,124

4

Density Temperature (°C)

Vertical density and temperature profiles compared


Fig. 6-18a, p. 169

Surface zone 2% of ocean water

80% of ocean waterPycnocline 18% of ocean water

Deep zone

Dep

th (

km)

The density zones

Increasing latitude (north or south)


Sound and light both travel in waves:

• Refraction is the bending of waves


Sunlight does not travel well in the ocean.

• Scattering occurs when light is bounced between air and water molecules, dust and other objects.

• Absorption occurs when light’s electromagnetic energy is converted to heat in the molecules of seawater.


Water Transmits Blue Light More Efficiently Than Red

Only a thin film of seawater is illuminated by the sun. Except for light generated by living organisms, most of the ocean lies in complete blackness.(a) The table shows the percentage of light absorbed in the uppermost meter of the ocean and the depths at which only 1% of the light of each wavelength remains.(b) The bars show the depths of penetration of 1% of the light of each wavelength (as in the last column of the table)


Fig. 6-22c, p. 173


Fig. 6-22d, p. 173


Sound in the Ocean

Sound Travels Much Farther Than Light in the Ocean


Fig. 6-23, p. 174

chapter 6 water. © 2006 brooks/cole, a division of thomson learning, inc. the water molecule is...

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