Water.ppt
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Transcript of Water.ppt
Water and the Fitness of the
Environment
Water - Polarity
• Water - simple, common, but exceptional– H2O - two Hydrogen and one Oxygen
– covers 75% of earth’s surface
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
Water - Polarity
Polar bonds between O and two H atoms– Oxygen is more electronegative
• in water, –O (slightly negative charge)–H (slightly positive charge)
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
Fig 2.12 Polar covalent bonds in a water molecule
Hydrogen Bonds
• Partial charges on atoms in water allow bonds to form between molecules – Hydrogen bonding
• results when H from one molecule is attracted to O of a different molecule
• partial positive attracted to partial negative
Fig 3.2 Hydrogen bonds between water molecules
1
4
32
hybrid s+3p orbitals
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
Fig 2.15 A Hydrogen bond between water and ammonia
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
partial pos.
partial neg.
Water - Polarity
• Hydrogen Bonding – between water molecules– gives water its special properties
Cohesion
Adhesion
Surface Tension
Temperature Moderation
Water Properties - Cohesion
• Cohesion– Binding together of like molecules by H bonds– High in water– H-bonds constantly breaking and reforming– most water molecules are bonded to
neighboring molecules at any instant– Contributes to water transport in plants
Water Properties - Adhesion
• Adhesion– Clinging of one substance to another unlike
substance– also involves H-bonds– also contributes to water transport in plants– water adheres to molecules of the walls of the
xylem vessels in plant stems (trunks) helps counter the effects of gravity
Cohesion and adhesion move water through plants
Water Properties - Surface Tension
• Surface Tension– Measure of how
difficult it is to stretch or break the surface of a liquid
– Higher in water than other liquids
– Ordered arrangement of water molecules at air-water interface
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 3.4
Water - Temperature Moderation
• Heat is the measure of the total amount of kinetic energy (energy of motion) in a body of matter
• Temperature is a measure of the intensity of heat due to the average kinetic energy of the molecules
• How does water moderate temperature?
Water - Temperature Moderation
• Water can absorb a lot of heat with only a small change in temperature– has a high Specific Heat
Water - Specific Heat
• Significance– A large body of water can absorb a large
amount of heat from the sun in daytime and during the summer, while warming only a few degrees.
– At night and during the winter, the warm water will warm cooler air.
– Stabilizes temperatures
Water - Temperature Moderation
• Liquids absorb heat as they evaporate– For water - 580 cal for each gram evaporated
• high compared with other liquids
– Heat of vaporization• Amount of heat a liquid must absorb for 1g
to be converted from liquid to gaseous state
Water - Heat of Vaporization
• Water’s high heat of vaporization – due to H bonding– results in “evaporative cooling”
• Hottest molecules evaporate, cooler molecules remain behind
• Cools oceans in tropics• Evaporation of sweat cools body
Fig 3.5 Hydrogen bonds in ice
• Are more “ordered” than in liquid water, making ice less dense
• Insulates the water it floats on
Ice WaterCopyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
Water - Solvent of Life
• Solution – Liquid that is a completely homogeneous
mixture of two or more substances
*** Sugar in water ***
Water - Solvent of Life
• Solvent - dissolving agent (water)
• Solute - substance that is dissolved (sugar)
• Aqueous solution - water is the solvent
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Water - Solvent of Life
• What happens when a solute dissolves in a solvent?
• Partial negative (O) and positive (H) charges on water molecule have affinity for positive and negative parts of solute
Fig 3.6 A crystal of table salt dissolving in water
Pos. charged Na+ ionscling to partial neg. charged O atomsof water molecules
Neg. charged Cl- ionscling to partial pos. charged H atomsof water molecules
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
Na+
Cl-
Water - Solvent of Life
• Other compounds besides ionic ones can also be solubilized
• Most will have regions that are polar– Partial pos. and neg. regions (like water)– May have some ionic regions, too– Proteins, DNA, etc.
Water - Solvent of Life
• Two categories of substances:– Hydrophilic (water-loving)
• compound with an affinity for water• polar or ionic compounds• can form H-bonds with water
– Hydrophobic (water-fearing)
• compounds which lack an affinity for water• non-polar compounds• lipids of the cell membrane• no H-bonding with water