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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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< 0o C - ice; 0o C - 100o C – liquid; > 100o C - steam

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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

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Water is Transparent

• The fact that water is clear allows light to pass through it

– Aquatic plants can receive sunlight– Light can pass through the eyeball to

receptor cells in the back