states of matter & bond strength –gas –gas = molecules not bonded to one another; move...
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States of Matter & Bond StrengthStates of Matter & Bond Strength
– GasGas = Molecules not bonded to one another; move independently. Takes the volume and shape of its container.
– LiquidLiquid = Molecules loosely bonded to one another; bonds easily broken, so liquids flow. Volume is fixed, but takes shape of container.
– SolidSolid = Molecules strongly bonded to one another; fixed size and shape. Bend or break with applied force.
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The Water MoleculeThe Water Molecule
º
If water weren’t polar, it would freeze at -90ºC (-130ºF) and boil at -68ºC (-90ºF).
And it wouldn’t be nearly so good a solvent (dissolver of salts etc).
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The Water MoleculeThe Water Molecule
(ice in glaciers & polar ice
caps)
(oceans, rivers, & lakes)
(water vapor in the
atmosphere)
Strongly bonded Loosely bonded Not bonded
Melting Evaporation
Condensation Freezing
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The Water Molecule - Types of BondsThe Water Molecule - Types of Bonds
• Covalent bondsCovalent bonds– Within each H2O molecule– Bonds the H’s to the O– Very strong! (sharing electrons)
• Hydrogen bondsHydrogen bonds– Between H2O molecules– Bonds H2O molecules to each other– Constantly forming and breaking in
liquid water
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The Water Molecule - Types of BondsThe Water Molecule - Types of Bonds
• High surface tensionHigh surface tension– Hydrogen bonding creates “skin”
– Important for living organisms• Capillarity (e.g., in vascular plants)
Cohesion
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The Water Molecule - Types of BondsThe Water Molecule - Types of Bonds
• Universal solventUniversal solvent– Electrostatic bonds between dipolar
water and ions• Ocean is salty ( NaCl Na+ + Cl– )
Adhesion
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B. B. Density & TemperatureDensity & Temperature
• Density ( Density ( ) ) = Mass / Volume = Mass / Volume (in g/cm3)
• Ratio, so if mass mass or if volume volume • Relative water density affects water-
current development
• Water-density vs. organism-density determines whether an organism will sink or float
– Some floating organisms can vary their density!
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Density & TemperatureDensity & Temperature• Density ( Density ( ) ) = Mass / Volume = Mass / Volume (in g/cm3)
• Most substances get denser (that is, have more mass per unit volume) as they get colder ( T T )
• This is only true for water down to ~4ºC (remember, water freezes at 0ºC)
• As water cools from ~4ºC to 0ºC, it becomes less dense! ( T T )
• The maximum density of fresh water ( maxmax ) is at 3.98ºC
• Let’s draw all that on a graphLet’s draw all that on a graph
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Temperature
D
ensi
ty
Density & TemperatureDensity & Temperature
““Normal” substanceNormal” substance
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Density & TemperatureDensity & Temperature
Temperature
D
ensi
ty
WaterWater
4ºC
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Density & TemperatureDensity & Temperature
(Fig. 6-3, p.102)
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Density & TemperatureDensity & Temperature
As T toward 4ºC:Amount of thermal motion Molecules occupy less volume (same mass) Density
As T from 4ºC to 0ºC:Molecules begin to line up to form ice crystals = Open, 6-sided structures Molecules occupy more volume (same mass) Density
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C. C. Heat & TemperatureHeat & Temperature• HeatHeat
– = Energy produced by the random vibration of atoms or molecules
– A measure of how many molecules are vibrating and how rapidly they’re vibrating
• TemperatureTemperature– = An object’s response to an input or
removal of heat– Records only how rapidly the molecules are
vibrating
• Heat Capacity Heat Capacity = a link= a link– = The amount of heat required to raise the
temperature of 1 gram of a substance by 1ºC
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Heat & TemperatureHeat & Temperature
º
(p.102)
1 calorie Amount of heat required to raise 1
gram of pure liquid water by 1ºC
VERY HIGH!
Water resists changing
temperature when it absorbs or releases heat
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D. D. Changes of StateChanges of State
Let’s draw all that on a graphLet’s draw all that on a graph (Fig. 6-6, p.104)
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