WATER ¾ of the Earth is covered with it Exists on Earth as a solid, liquid AND gas POLAR!!!

Do you remember? 2  What are the three main types of bonds?  Ionic, covalent, metallic  How do you predict which type will form?  Metal-non or non-non or metal-metal  What will O and H form? Why?  covalent bonds between H and O.  Because they are both nonmetals  But they have a special type of covalent bond called…POLAR.

There are really 4 types of bonds you must know: 3 1. Metallic 2. Ionic 3. Nonpolar Covalent 4. Polar Covalent How do you know which type will form???

There are four types of bonds you must know: 4 1. Metallic- 1. metal with a metal 2. Ionic 1. Metal with a nonmetal 2. OR if their electronegativities have a difference above 1.7

There are four types of bonds you must know: 5 3. Nonpolar Covalent: -Nonmetal with a nonmetal -If two of the same element -or if their electronegativity difference is ZERO-.3

There are four types of bonds you must know: 6 4. Polar Covalent: -Nonmetal with a nonmetal -Electronegativity difference is between 0.4 and 1.6 -If Nitrogen, Oxygen or Fluorine are one of the elements, they are VERY electronegative and will hog the electrons… Therefore NOF’s create POLAR COVALENT BONDS!

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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  So…the region around oxygen has a partial negative charge.  The region near the two hydrogen atoms has a partial positive charge. 8

This leads to a new type of bond…  Called a…

10 Hydrogen bond

Hydrogen Bonds  Not really a bond.  Occur between molecules (not within)  Bonds within water molecules are POLAR COVALENT!!!  Very Weak  Can break and reform

HYDROGEN BONDS  The hydrogen bonds joining water molecules are weak, about 1/20 th as strong as covalent bonds.  They form, break, and reform with great frequency 12

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

14 Hydrogen bonds affect the properties of waterr

Special Arrangement:  Water molecules arrange themselves in a very specific way…  WHY??? 15

16  The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.1 OPPOSITES ATTRACT Form between the H and O ends of nearby molecules

BUT Like charges repel each other… 17 H and H repel each other, as do O and O

Which will form?

Organisms Depend on H bonds…  Cohesion – water molecules sticking to each other (by H bonbds)  plays a key role in the transport of water against gravity in plants  Adhesion- water molecules stick to other things  Like the meniscus! 19

20 Surface tensionMeniscus-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!!!

23 Ice, water, vapor

24 Hydrogen bonding (electric attraction) IceLiquid

Density of Water 25 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 substances Most 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.

Hydrophilic dissolves Hydrophilic WILL DISSOLVE: Ionic Compounds, Polar Molecules (anything with a charge) Water

Hydrophobic dissolves Hydrophobic WILL DISSOLVE: only nonpolar, hydrophobic things (things with NO CHARGE) Oil

Food Coloring Demo  Food coloring does not dissolve in oil because it is polar and oil is NONPOLAR.

So what about oil and water? 32

Solvent for Life  Solution  Solute  Solvent  Hydrophilic  Ionic compounds dissolve in water  Polar molecules (generally) are water soluble  Hydrophobic  Nonpolar compounds 33