1. Water 2.2

2. Essential Idea: Water is the medium of life.
2.2
Water
Understandings:
Water molecules are polar and hydrogen bonds form between them.
Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water
Substances can be hydrophilic or hydrophobic
Applications:
Compare the thermal properties of water with those of methane
Use of water as a coolant in sweat
Modes of transport of glucose, amino acids, cholesterol, fats, oxygen and sodium chloride in blood in relation to their solubility in water

3. Quick Review: Covalent Bonding
Atoms share electrons
Can have single, double, triple bonds
Relatively strong bonds
Many different types for specific kinds of molecules (ex. peptide, glycosidic, phosphodiester)

4. Water Polarity: Uneven distribution of charges around a molecule
Hydrogen side of water molecule is slightly positive while oxygen side is slightly negative
Attraction between positive side of one water molecule and negative side of next = Hydrogen bond

5. One hydrogen bond is weak, but a drop of water contains millions and millions, making water very strong

6. Water forms into droplets (which join together when close)
Cohesion –
Water forms into droplets (which join together when close)
Water has strong surface tension (remember penny lab?) Water can move as a column in plants
(1:55)

7. Adhesion - Attraction between water molecules and other types of molecules
Also at play in movement of water in vascular plants (capillary action) - Once water moves into the vascular tissue, adhesion keeps it from dropping back down

8. Thermal Properties
High Specific Heat – water can absorb a lot of heat without changing temperature
 Moderate climate near large bodies of water
 Living things contain large amounts of water – helps stabilize body temp

9. High Heat of Vaporization – have to add a lot of heat to get water to evaporate
Coolant – When you sweat, the sweat absorbs your body heat in order to evaporate
High Boiling Point – liquid over a broad range of temperatures

10. Water Methane Polarity Polar Non-polar Hydrogen Bonds Yes No
Compare the Thermal Properties of Water and Methane
Water
Methane
Polarity
Polar
Non-polar
Hydrogen Bonds
Yes No
Boiling Point
100 degrees C
-162 degrees C
Freezing Point
0 degrees C
-183 degrees C

11. Solvent Capable of dissolving an abundance of other molecules
Makes it extremely valuable in transporting molecules
Water being transported by cohesion and adhesion in plants is carrying dissolved substances everywhere it goes
Blood is composed mainly of water – carries dissolved substances around your body (glucose, ions, amino acids)
Also makes it an excellent medium for metabolic reactions
*Remember
Solvent = substance doing the dissolving
Solute = substance that gets dissolved
Together they make a solution

12. Hydrophilic molecules – molecules that dissolve in water
Generally polar (like likes like)
Ex. glucose and other carbohydrates, ions such as sodium (Na+, Ca++, Cl-)
Hydrophobic molecules – don’t dissolve in water
Generally non-polar
Ex. Lipids, methane

13. Hydrophobic Interactions - There is often a slight
attraction between non-polar molecules, and they
avoid water together

14. ***Whether a molecule can be dissolved by water or not determines how easily it can be transported in the body***
Is It Soluble?
Yes No

15. Less dense in solid form
Ice floats – insulates large bodies of water to keep them from freezing entirely (life can survive the winter)
Forms habitat for some species