Transcript Structure & Properties of Water

Structure & Properties of
Water
STRUCTURE
OF WATER
UNIVERSAL
SOLVENT
DENSITY
COHESION
POLAR
MOLECULE
CAPILLARY
ACTION
ADHESION
SURFACE
TENSION
SPECIFIC
HEAT
BUOYANCY
STRUCTURE OF WATER
H
H
O
1 molecule of water is
made up of 2 hydrogen atoms
bonded with 1 oxygen atom
STRUCTURE OF WATER
O
The bond that forms water
is a covalent bond
CHEMICAL FORMULA
H2O = RIGHT
2
H O = WRONG
H2O = WRONG
2HO = WRONG
H
H
O
1 molecule of water
A LOT OF MOLECULES
OF WATER
Millions of molecules of water
make up 1 raindrop
POLAR MOLECULE
• A molecule that has electrically charged
areas.
• Also called a polar substance or polar
compound.
+
DURACELL
_
NON-POLAR SUBSTANCES
• Non-polar substances do not have
charged ends
DURACELL
+
+
H
H
O
-
POLAR MOLECULE
H
O
H
The positive hydrogen ends of 1
molecule are attracted to the negative
end of the oxygen of another molecule.
POLAR MOLECULE
THE PROPERTIES OF:
Cohesion, adhesion, specific heat, universal
solvent, capillary action, surface tension
ALL HAPPEN BECAUSE WATER IS A
POLAR SUBSTANCE!
CAPILLARY ACTION
CAPILLARY ACTION
• The combined force of attraction
among water molecules and with the
molecules of the surrounding
material.
• Cohesion + Adhesion
SURFACE TENSION
SURFACE TENSION
SURFACE TENSION
SURFACE TENSION
• The tightness across the surface of water
that is caused by the polar molecules
pulling on one another.
• Makes the surface act like a solid
UNIVERSAL SOLVENT
UNIVERSAL SOLVENT
• This is a nickname given to water.
• Water dissolves LOTS of things.
• Remember:
SOLVENT = the thing doing the dissolving
SOLUTE = the thing that dissolves away
• Other polar molecules can be dissolved by
water.
NON-POLAR SUBSTANCES
DURACELL
• Non-polar substances DO NOT dissolve in
water.
• Can you think of some examples of nonpolar substances?
Universal Solvent
Why is water so good at dissolving things?
Because water is a polar molecule and is
shaped like a wedge, it is able to break up
substances into smaller pieces (dissolve).
COHESION
H
O
H
• Because water is a polar molecule, it
is attracted to itself.
• Cohesion – is the attractive force
between water molecules.
COHESION
Water molecules
like to stick to
each other.
Rubbing alcohol
doesn’t like to
stick to itself as
much as water.
ADHESION
• Because water is a polar molecule, it
is attracted to other substances.
• Adhesion – occurs when molecules
of water are attracted to other
substances.
WINDSHIELD
Adhesion is going
on between the
windshield and the
water droplet.
WATER
DROPLET
ADHESION
COHESION
Water molecules like to stick
to each other.
ADHESION
Water molecules like to stick
to other things.
Density of Water
• Most dense at 4oC
• Contracts until 4oC
• Expands from 4oC
to 0oC
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.
– When water reaches 0oC, water becomes
locked into a crystalline lattice with each
molecule bonded to to the maximum of four
partners.
– As ice starts to melt, some of the hydrogen
bonds break and some water molecules can
slip closer together than they can while in the
ice state.
– Ice is about 10% less dense than water at 4oC.
Fig. 3.5
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
SPECIFIC HEAT
• Specific Heat = the amount of energy
needed to increase the temperature of
something 1 degree C.
• Water has a really HIGH specific heat
• That means it takes a lot of energy for
water to increase its temperature.
• This is because of the STRONG
ATTRACTION between water molecules.
It’s POLAR!
SPECIFIC HEAT
WATER = 75°F
BEACH = 200°F
SPECIFIC HEAT
METAL = 500
CLOTH = 1340