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Polar Covalent vs. Nonpolar Covalent
• Polar covalent- which means 2 different nonmetals (ex. water or ammonia) (have opposite charges on molecule b/c electrons are more attracted to oxygen)
• Nonpolar Covalent- means 2 of the same nonmetals (ex. Oxygen or nitrogen gas) and they do not have opposite charges and share electrons equally.
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• Water consists of an oxygen atom bound to two hydrogen atoms by two single polar covalent bonds.
– Oxygen has unpaired & paired electrons which gives it a slightly negative charge while Hydrogen has no unpaired electrons and shares all others with Oxygen
– Leaves molecule with positively and negative charged ends
Water is a Polar Molecule-has oppositely charged
ends
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slightly positive charge
slightly negative charge
hydrogen bond between (+) and (-) areas of different water molecules
Water molecules form Hydrogen bonds
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Water’s Properties
• Surface Tension• Cohesion• Adhesion• Hydrophilic• Hydrophobic• Solid water (ice) is less dense than liquid• Solvent• Transparent
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Cohesion• How water molecules cling together by hydrogen bonding
• -water molecules stick together to climb up a stem
– Cohesion refers to attraction to other water molecules.
responsible for surface tension
a measure of the force necessary to stretch or break the surface of a liquid
Hydrogen bonding allows water to behave like its coated w/ an invisible film
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– Adhesion –how water molecules can stick to different things;
– Water molecules stick to a plant’s stem & climb up a plant to reach the leaves to do photosynthesis
– refers to attraction to other substances.
Adhesion
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Capillary actionwater evaporates from leaves = transpiration
adhesion, cohesion and
capillary action
All thanks
to hydrogen
bonding!
water taken up by roots
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•trees have specialized structures to transport water: xylem and phloem “plumbing”
• water molecules are “dragged” from the roots to the top of the tree by capillary action and cohesion: hydrogen bonds help water molecules to each other
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• Water is an effective solvent as it can form hydrogen bonds.
– Water clings to polar molecules causing them to be soluble in water.
Hydrophilic - attracted to water (likes water); usually ionic or polar substances (ex. Salt)
Hydrophobic - repelled by water
Usually non-polar/non-ionic substances
ex. oil
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“Universal” Solvent• A liquid that is a completely homogeneous
mixture of two or more substances is called a solution.
– A sugar cube in a glass of water will eventually dissolve to form a uniform mixture of sugar and water.
• The dissolving agent is the solvent and the substance that is dissolved is the solute.
– In our example, water is the solvent and sugar the solute.
• In an aqueous solution, water is the solvent.
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• Water transports molecules dissolved in it– Blood, a water-based solution, transports
molecules of nutrients and wastes organisms
– Nutrients dissolved in water get transported through plants
– Unicellular organisms that live in water absorb needed dissolved substances
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Solid water (ice) is less dense than liquid
same mass but a larger volume
• Ice is less dense than water: the molecules are spread out to their maximum distance
Density = mass/volume
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water expands as it solidifies
water reaches maximum density at 4 degrees C
water freezes from the top down
organisms can still live in the water underneath the ice during winter
Oceans and lakes don’t freeze solid because ice floats