2.1 What Does Life Require?

Water

Water on Earth

Can exist in all 3 physical statesLiquidSolidGas

Not all animals must drink liquid water.Can get water from food.Can get water through metabolism of glucose.

Water on EarthSource % of Supply

Oceans 97.08

Ice Sheets and Glaciers 1.99

Ground Water 0.62

Atmosphere 0.29

Lakes (Fresh) 0.01 Inland Seas / Salt Water Lakes

0.005

Soil Moisture 0.004

Rivers 0.001

Water

Water is the solvent, the medium and the participant in most of the chemical reactions occurring in the environment.

On earth, water is found as a liquid, as a solid (ice) or as a gas (water vapor).

Water molecules are attracted to each other, creating hydrogen bonds.

These strong bonds determine almost every physical property of water and many of its chemical properties.

Why does the electron stay in orbit around the nucleus?

The Properties of Water

A molecule consists of two or more atoms held together by chemical bonds

Chemical bonds occur between two atoms in a molecule that share electrons

Water is a molecule made up of two hydrogen atoms and one oxygen atom that are bonded together by shared electrons

In a water molecule, the two hydrogen atoms each share one electron with the oxygen. This gives each hydrogen atom two electrons in their outer shell (the ideal number for shell 1), and the oxygen atom eight in its outer shell (the ideal number for shell 2).

The Properties of Water

Oxygen is more electronegative (electron-pulling) than hydrogen

The electrons in water spend more time near the nucleus of the oxygen atom than near the nuclei of the hydrogen atoms

δ- symbolizes a partial negative charge δ+ symbolizes a partial negative charge

The Properties of Water

The unequal sharing of electrons makes water a polar molecule, since different regions (poles) of the molecule have different charges

When atoms of a molecule carry no charge, they are nonpolar (do not have differing charges)

The Properties of Water

Water molecules tend to orient themselves so that the partially positive charged hydrogen atom of one molecule oxygen atom (with partial negative charge) of another molecule

The Properties of Water

The weak attraction between the hydrogen atom and the oxygen atom is a hydrogen bond

Hydrogen bonding is a weak chemical bond occurring between hydrogen and another atom based on the attraction of partial charges for each other

Cohesion

Water molecules stick to each other. The attraction between the water molecules is

greater than the attraction between water and air. creates a surface tension (film)permits water to hold up substances heavier and

denser than itself. steel needle carefully placed on the surface of a glass of

water will float.

Cohesion of water

molecules permits the flow of water in streams and rivers.

Surface tension is essential for the transfer of energy from wind to water to create waves which are necessary for rapid oxygen diffusion in lakes and seas.

Some aquatic insects such as this water strider (predators on smaller invertebrates) rely on surface tension to walk on water.

Adhesion Water molecules bind to many other

substances such as glass, cotton, plant tissues, and soils.

For example, in a thin glass tube, when the molecules at the edge reach for and adhere to the molecules of glass just above them, they tow other water molecules along with them due to cohesion. The water surface, in turn, pulls the entire body of water to a new level until the downward force of gravity is too great to be overcome. This process is called capillary action.

Adhesion Adhesion allows the flow

of water through the vascular tissues of plants and the flow of blood through blood vessels.

Adhesion

Adhesion also produces viscosityWater flows in layers

Laminar viscosity: friction between layers

Flow is fastest in middle

Slowest near edges of stream and bottom due to friction of layers

Laminar viscosity: friction between layers of water. Flow is fastest in middle, and slowest near edges of stream and bottom due to friction between layers.

The Properties of Water

Water is called the universal solventMany things (solutes) dissolve in water

Chemical reactions occur when the reactants (starting materials) are converted into products (end materials)Dissolving facilitates chemical reactions

The Properties of Water

Salt water is a solution of the salt sodium chloride

Water is able to dissolve sodium chloride, which is a direct result of its polarity

Polar molecules are hydrophilic (water loving) because of their ability to dissolve in water

The Properties of Water

Salts are produced by the reactions of an acid (a substance that increases the concentration of hydrogen ions in a solution) with a base (a substance that reduces the concentration of hydrogen ions in a solution)

The pH scale is a measure of the relative amounts of these ions in a solution

The Properties of Water

pH measures the amount of H+ ions in a solution

Acids have a lot of H+ ions in solution Bases have less H+ ions in solution The pH scale

Low numbers (1-6) acidic7 is neutralHigh numbers (8-14) basic

The Properties of Water

Nonpolar molecules, such as oil, do not contain charged atoms

These atoms are called hydrophobic (water hating)

Water’s High Specific Heat

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

Therefore, the specific heat of water is defined as

1cal/gram/oC

How Water Stabilizes Temperature Water’s high specific heat is linked to hydrogen

bonding. Much of the heat energy is used to disrupt the

hydrogen bonds before the water molecules can begin moving faster.

When the temperature of the water drops slightly, many hydrogen bonds form, releasing a considerable amount of energy in the form of heat.

High Heat Capacity

Water absorbs or releases more heat than many substances for each degree of temperature increase or decrease. Warms slowlyCools slowlyEvaporative cooling: sweating, evapo-

transpiration in plants

High Heat Capacity

Differences in temperature between lakes and rivers and the surrounding air may have a variety of effects. Local fog or mist is likely to occur if a lake

cools the surrounding air enough to cause saturation; small water droplets are suspended in the air.

High Heat Capacity

Water vapor forms a kind of global "blanket" which helps to keep the earth warm. Heat radiated from the sun-warmed surface of

the earth is absorbed and held by the vapor. Water vapor contributes to global warming

Is it a greenhouse gas?

High Heat Capacity

Large bodies of water, such as the oceans or the Great Lakes, have a profound influence on climate. Heat reservoirs and heat exchangersSources of moisture that falls as rain and snow

over adjacent land masses.When water is colder than the air, precipitation is

curbed, winds are reduced, and fog banks are formed.

Freezing and Boiling

Pure water at sea level boils at 100°C and freezes at 0°C. At higher elevations (lower atmospheric pressures) water's boiling temperature decreases. Takes longer to boil an egg at higher altitudes

Doesn’t get high enough to cook the egg properly

If a substance is dissolved in water, the freezing point is lowered.

Spread salt on streets in winter to prevent ice formation.

Biological Antifreeze

Must prevent formation of ice crystals inside cells. Insects cells replace water with glycerolPlants use sugars and proteins to increase

solutes in the cytoplasmAntarctic fish use glycoproteins

Water Vapor

Absolute humidity: actual mass of water vapor in the air

Relative humidity: % of max. water vapor for a particular temperature

Dew point: saturation point for a particular temperature

Air Temp. and Humidity

Warm air holds more water vapor than cold air. This explains why indoor air is so dry in

winter. Cold air outside holds little water. Air coming into house is dry. Heating dries it further.

Absolute Humidity

Chicago’s Weather

• There are two geographical factors that contribute to Chicago's weather.– Lake Michigan: 450 miles long, 80 miles

wide, 900 feet deep. – Location: there really aren’t any major

geographical features to the west or south of Chicago for nearly a thousand miles (1600 kilometers).

• Location effect

– Once weather events start heading to Chicago, there is nothing in the geography to stop them.

– This means that there are usually two to three days warning before any major weather systems hit Chicago.

– This also means that any weather system that happens to head to Chicago tends to get there.

– This makes Chicago weather very variable in the long term.

– But it also tends to be predictable in the short term.

• Lake effect

– As any huge mass of water does, Lake Michigan makes a dandy thermal mass.

– It tends to be much warmer that the air over it in winter, and much cooler than the air in summer.

– In winter, this bring lake effect snows that can drop six inches of snow on downtown while leaving the suburbs dry.

– In summer, this brings the lake breeze, which can drop the temperature dramatically downtown, while it’s broiling hot in the western ‘burbs.

• This also explains why NW Indiana, SE

Michigan, and Buffalo, N.Y. are hit so hard by snowstorms in the winter. – As air passes over the warm lake water, it

picks up moisture. – Then as it passes over the land, it cools

and drops its moisture in the form of snow.