Chapter 4 Section 4
Unique Properties of
Water
Mrs. Kerstetter
Biology
Structure of Water




All living things are dependent on water
Cells are surrounded by fluid that is mostly
water
Cells are 70-95% water
Formula for water?
H2O
 H atoms are joined to O atoms by a single
covalent bond
Key to water’s unusual properties:
1.
2.
3.
Electrons of each covalent bond are not
shared equally between the H & O atoms
Oxygen has a stronger attraction
The unequal sharing causes the Oxygen to
have a slightly negative (-) charge, while the
hydrogen ends have a slightly positive (+)
charge
Polarity

A molecule in which opposite ends have
opposite electrical charges is called a POLAR
molecule

Water is a polar molecule
How are water molecules attracted to
each other?

Slightly negative O attracts the slightly positive
hydrogen of adjacent molecules, causing
molecules to become arranged using hydrogen
bonds
Water’s Unique Properties
1.
2.
3.
4.
Cohesion and Adhesion
Temperature Moderation
Low Density of Ice
Ability to Dissolve Other Substances
Cohesion and Adhesion

Cohesion



tendancy of molecules of the same kind to stick to one
another
Much stronger for water than other liquids
Adhesion

Attraction between unlike molecules
Important to keep large groups of molecules organized in living
world
Temperature Moderation

Thermal energy


Total amt of E associated with the random
movement of atoms and molecules in a sample of
matter
Temperature
Measure of the average E of random motion of
particles in a substance
 Is temperature transferred from warmer to cooler or
cooler to warmer?


Warmer to cooler
Temperature Moderation

Temperature rises bc the molecules move faster

In water, some of the E goes to break bonds, so
doesn’t heat as fast

When you cool a substance the molecules slow and
temp drops BUT

In water, it forms H bonds, so doesn’t cool as much as a
metal
Examples of Temp Moderation of
Water

Oceans and lakes moderate the temperature of
nearby land masses


El Nino
Evaporation and sweat
Low Density of Ice


Formula for ice?
Water is more dense than ice
Why?
 Hydrogen bonds
 Longer lived bc slower moving
than liquid form

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Why is this important to living things?
Ability to Dissolve Other Substances

Solution

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
Solute


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Substance that is dissolved and present in a lesser amount
salt
Solvent



Uniform mixture of 2 or more substances
Salt water
Substance that dissolves the other substance and is present in a greater
amount
water
Aqueous solution

When chemical dissolved in water
Main Solvent


Water is the main solvent in all cells and in plant
sap
Polar molecules are easily broken down by water