The Properties of Water
2.9 Unequal electron sharing creates a polar molecule
1. Structure:
1 Oxygen Atom and 2 Hydrogen Atoms Covalently Bonded together (H always shares electrons)
2. Its structure makes it a Polar Covalent Molecule:
Covalent: Formed by the unequal sharing of Valence electrons
Polar: Has a positive and negative end
Makes Oxygen more Electronegative
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2.10. Hydrogen bonds are weak bonds important in the chemistry of life
a. Forms Hydrogen Bonds:
A Hydrogen Bond is a weak bond formed between atoms of Hydrogen and Oxygen, Carbon, Nitrogen or F (Any atoms with high ) One Hydrogen Bond is Weak.... Many are strong!!
2.11. H Bonds make liquid water cohesive= a. Cohesion: an attraction between molecules of the same substance
Creates Surface Tension
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b. Adhesion: attraction between molecules of different substances ex. water beads on glass
Also caused by waters ability to H­Bond
Capillary Action
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Surface Tension caused by hydrogen bonding between water molecules...create a net of molecules
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How many H­Bonds come into contact with the paper clip?
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How many H­Bonds come into contact with the paper clip?
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Paper Clip weighs= 1 gram
Each H bond can support 0.25 g of weight before breaking
Will it float?
Why or Why Not?
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Will it float?
Why or Why Not?
1 g
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0.25+0.25+0.25+0.25= 1 gram can be supported
View from the Top
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The weight of the paper clip is evenly distributed over more bonds which can support its weight.
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2.12 Water's H­Bonds moderate Temperature
A. High Heat Capacity:
Heat: Measure of energy associated with
movement of molecule
Temp: Measure of the intensity of heat
H bonds break when heat is added, but that energy is absorbed by surrounding molecules
This means, water can absorb a lot of energy
without changing temp.
It also slows the rate at which water is cooled!!!
Maintains a relatively stable water temp over drastic changes in land temp!!!
(ie...cold sand in morning....scolding hot in the afternoon, but the water stays about
the same)
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Evaporative Cooling: Sweating
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B. Evaporative cooling:
Heat causes molecules to move faster.
As water molecules absorb heat they evaporate,
taking that energy with them.
This leaves cooler water molecules behind
(Why sweating cools you down!!!)
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2.13 Ice is Less Dense than Water
AS TEMP declines Water Molecules H­Bond with adjacent molecules forming a crystal
This is less dense than Liquid water whose H­bonds are constantly being broken and reformed: Allows ice to float on top of water, Insulating large bodies.
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2.14. Water is the Solvent of Life
Forms Solutions and Suspensions
Water is known as the Universal Solvent. (Aqueous Solutions) Its primary reason for importance is that food that we rely on for energy is dissolved in water and efficiently transported throughout our bodies.
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1. Solution: A Homogenous mixture in which the atoms of a substance completely dissociate in another substance
Dissociate means to separate or break apart
a. Solute: Thing being dissolved or dissociated (ie...Salt)
b. Solvent: Thing doing the dissolving or dissociating (ie...Water)
2. Suspension: Mixture in which the particles are too large to completely dissociate
(ie...Milk or Fog) 14
C. Acids and Bases
H+= Hydrogen Ion
OH­= Hydroxide Ion
Acid= H+ ion Donor or an OH­ receptor
Base= OH­ ion Donor or an H+ receptor
pH­ measure of the concentration of
H+ ion
The more H+..the lower the number...but stronger the acid
Chemical with a a. pH of 0­6.9 are acids
More H+ than OH­
b. pH of 7.1­14 are bases
More OH_ than H+
c. pH of 7 are neutral
H+ and OH­ are equal
Water is neutral because it acts as both an
acid and a base
Dissociation of Water into an ACID and a BASE
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H2O
OH­ (Hydroxide ion)
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H+ (Hydrogen Ion)
When water breaks apart it gives off both H+ and OH­ ions, therefore making it both an
___________ and a _________
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Water Acts like a Biological
BUFFER
Carbonic Acid Bicarbonate Buffer System
Normal Blood pH= 7.4
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