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