WATER

¾ of the Earth is covered with it

Exists on Earth as a solid, liquid AND gas

POLAR!!!

Do you remember the 3 types of bonds we taught earlier in the year?

2

1. Metallic2. Ionic3. Covalent- actually there are two types…

1. Polar Covalent2. Nonpolar Covalent

How do you know which type will form???

So actually- there are four types of bonds you must know:

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1. Metallic- 1. metal with a metal

2. Ionic1. Metal with a nonmetal

The four types of bonds you must know:4

3. Nonpolar Covalent:-Nonmetal with a nonmetal

-If two of the same element

The four types of bonds you must know:5

4. Polar Covalent:-Nonmetal with a nonmetal- Both are different elements

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Water background rewind

What elements are in a water molecule? What type of bond will form between

them? How do you know it will be a polar

covalent bond? _______________ with a ____________

Polarity of Water

A water molecule is a polar molecule with opposite ends of the molecule with opposite charges. oxygen is more electronegative so it pulls on

the electrons more the OXYGEN end has a slight negative

charge. The HYDROGEN end has a slight positive

charge.

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This leads to a new type of “bond”…

Called a…

10Hydrogen bond

Hydrogen Bonds

Not really a bond. Occur between molecules (not within)

Bonds within water molecules are POLAR COVALENT!!!

HYDROGEN BONDS

As far as BOND go, they are very weak, about 1/20th as strong as covalent bonds.

They form, break, and reform with great frequency

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Each water molecule can form hydrogen bonds with up to four neighbors.

Polar Covalent- greenHydrogen bonds- orange

15Hydrogen bonds affect the properties of water

Special Arrangement:

Water molecules arrange themselves in a very specific way…

WHY???

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OPPOSITES ATTRACT

BUT Like charges repel each other…

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What two ends of the molecule attract each other?

Hydrogen and Oxygen What will be repelled by each other?

O + O and H + H

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 3.1

Which will form?

Circle which will form on your notes packet…

Organisms Depend on H bonds…

Cohesion – water molecules sticking to each other (by H bonds) plays a key role in the

transport of water against gravity in plants

Adhesion- water molecules stick to other things Like the meniscus!

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22Surface tension

Meniscus- adhesion

Surface Tension- cohesion

Hydrogen Bonds affect the DENSITY of water

USUALLY a solid is more dense than the liquid or gas form:

NOT TRUE FOR WATER!

Due to the H bonds- water actually EXPANDS ( and is less dense than water) when it FREEZES!!!

Density of Water25

The density of water:

1. Prevents water from freezing from the bottom up.

2. Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation.

3. Makes transition between season less abrupt.

Are you afraid of water?26

What do you think the following two words mean?

Hydrophilic Hydrophobic

Hydro means water, philic and phobic refer to whether or not it “likes” water

Hydrophilic vs Hydrophobic

Hydrophilic Any substance that likes water (WATER-

LOVING)Ionic or polar substancesMost hydrophilic substances dissolve

in water (ex salt) Hydrophobic: any substance that

doesn’t like water (WATER –FEARING)

Usually nonpolar/non-ionic substance (ex-oil)

“Like Dissolves Like”28

Polar Solutions (like water) are able to dissolve other polar molecules as well as ionic compounds. Why?

Likewise, nonpolar solutions (like oil) will not dissolve polar and ionic compounds and will instead dissolve NONPOLAR molecules.