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. Metallic 2. Ionic 3. Covalent- actually there are two types… 1. Polar Covalent 2. Nonpolar Covalent How do you know which type will form???

So actually- there are four types of bonds you must know: 3 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

The four types of bonds you must know: 4 3. Nonpolar Covalent: -Nonmetal with a nonmetal -If two of the same element -or if their electronegativity difference is ZERO-.3

The four types of bonds you must know: 5 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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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 ____________  EN difference of___________

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 OXYGEN end has a slight negative charge.  The HYDROGEN end has a slight positive charge. 8

This leads to a new type of “bond”…  Called a…  Any guesses?

10 Hydrogen bond

Hydrogen Bonds  Not really a bond.  Actually Intermolecular Forces/ “attractive forces”  Occur between molecules (not within)  Bonds within water molecules are POLAR COVALENT!!!

HYDROGEN BONDS  As far as BOND go, they are weak, about 1/20 th as strong as covalent bonds.  BUT STRONG for an intermolecular force…  They form, break, and reform with great frequency 12

 Each water molecule can form hydrogen bonds with up to four neighbors. ** Color the polar covalent bonds one color and hydrogen bonds another color in your notes right now…

Polar Covalent- green Hydrogen bonds- orange

15 Hydrogen bonds affect the properties of water

Special Arrangement:  Water molecules arrange themselves in a very specific way…  WHY??? 16

OPPOSITES ATTRACT

BUT Like charges repel each other… 18 H and H repel each other, as do O and O

19 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 The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond.

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! 21

22 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!!!

25 Ice, water, vapor

26 Hydrogen bonding (electric attraction) IceLiquid

Density of Water 27 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? 28  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  Hydrophobic: any substance that doesn’t like water  (WATER –FEARING) Usually nonpolar/non-ionic substance (ex-oil)  Hydrophilic  Any substance that likes water (WATER-LOVING) Ionic or polar substances Most hydrophilic substances dissolve in water (ex salt)

“Like Dissolves Like” 30  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

 Label the following as: W= water soluble O= oil soluble B = soluble in both  Ionic Compounds__________  Nonpolar molecules _______  Things with NO charge________  Polar Molecules________  anything with a charge_________  hydrophobic things_________  hydrophilic things_________ 

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

So what about oil and water? 35