PROPERTIES OF WATER
Cohesion
Cohesion refers to the attraction between water
molecules. Hydrogen bonds are weak bonds between
adjacent water molecules. Hydrogen bonds are what
causes water molecules to stick together or have
cohesion.
Hydrogen bonds are constantly breaking and new bonds
are formed with different molecules. Have you ever
watched water drip from a leaky faucet or from a melting
icicle? If you have, then you know that water always falls
in drops rather than as separate molecules. Dew drops are
another example of water molecules sticking together
through cohesion.
Due to water's cohesiveness:

Liquid water has surface tension. This allows for
insects, such as Water Striders, to walk on water.

Water is a liquid at moderate temperatures, and not
a gas.
Surface Tension
Surface tension is a measure of the force necessary to
stretch or break the surface of a liquid. It is related to
cohesion. Cohesion refers to the attraction between
water molecules. Cohesion is responsible for surface
tension.
Water has a greater surface tension than most other
liquids because hydrogen bonds among surface water
molecules resist stretching or breaking the surface. Water
behaves as if covered by an invisible film.
Some
animals can
stand, walk,
or run on
water without
breaking the
surface.
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Adhesion
Cohesion refers to the attraction between water
molecules, while adhesion refers to attraction to
other kinds of molecules.
Water is adhesive to any molecule it can form
hydrogen bonds with. Water will make hydrogen
bonds with other surfaces such as glass, soil, plant
tissues, and cotton.
On extremely clean/smooth glass, water may form a
thin film because the molecular forces between
glass and water molecules (adhesive forces) are
stronger than the cohesive forces.
Capillary Action
Cohesion refers to the attraction between
water molecules, while adhesion refers to
attraction to other kinds of molecules
(see picture above). Capillary action
happens because water has both adhesive
and cohesive properties.
In capillary action, water is attracted to a
substance through adhesion. Then
because of cohesion, other water
molecules move too. For example, when
you have a narrow
tube in water, the
water will rise up the tube
because of water's adhesiveness
to the glass and cohesiveness to
other water molecules.
Capillary action is also what
causes water to move through
plants and a paper towel to soak
up water.
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Solvent
Water is able to dissolve more substances than any
other liquid - even the strongest acid! Because of
this, it is often called the 'universal solvent.'
When the two hydrogen atoms bond with the
oxygen, they attach to the top of the molecule
rather like Mickey Mouse ears. This structure gives
the water molecule polarity, or a lopsided electrical charge that attracts other atoms. The end of the
molecule with the two hydrogen atoms is positively charged. The other end, with the oxygen, is
negatively charged. Just like in a magnet, where north poles are attracted to south poles ('opposites
attract'), the positive end of the water
molecule will connect with the negative end
of other molecules.
Water's polarity allows it to dissolve other
substances very easily. When a substance is
put in water, the positive ends of its
molecules are attracted to the negative ends
of the water molecules, and vice versa. The
attractions cause the molecules of the new
substance to be mixed uniformly with the
water molecules.
Specific Heat
Why do coastal areas tend to have more
consistent temperatures throughout the
year while areas that are farther inland
have more extreme highs and lows? This is
due to water's high specific heat. Specific
heat is the amount of energy required to
change the temperature of a substance.
Because water has a high specific heat, it
can absorb large amounts of heat energy
before it begins to get hot. It also means that water releases heat energy slowly when situations cause it
to cool. Water's high specific heat allows for the moderation of the Earth's climate and helps organisms
regulate their body temperature more effectively.
It takes a lot of energy to change the temperature of water
because it takes a lot of energy to break the hydrogen bonds.
Water absorbs and stores a large amount of heat from the sun
and, as it cools, it releases this heat into the air that travels onto
land. So in winter, when the air is colder than the water, the air
literally picks up the water's heat as it passes over it onto land
and warms it. Likewise, in the summer when the air is hotter than
the water, the air cools off as it travels past the ocean to land and
cools the shore. This is what helps keep moderate temperatures
in coastal regions throughout the year.
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Evaporation
Water's high heat of evaporation is basically the amount of
heat energy needed to change a gram of liquid into gas.
Water needs a lot of energy in order to break down the
hydrogen bonds. The evaporation of water off a surface
causes a cooling effect.
When you get too
hot, your body
cools down by releasing water through pores in your skin. This
heat from your sweat, which is mostly water, is removed by the
air much like the heat from the ocean along the coast. As the
heat is removed, you become cooler, and this process is called
evaporative cooling.
Evaporative cooling is responsible for moderating earth’s
climate, stabilizing temperatures in aquatic ecosystems, and
preventing organisms from overheating.
Density
Water is less dense as a solid! At
cooler temperatures, the hydrogen
bonds of water molecules form ice
crystals. The hydrogen bonds are
more stable and will maintain its
crystal-like shape.
Ice—the solid form of water—is less
dense than water because of the
hydrogen bonds being spaced out
and being relatively apart. In ice,
each molecule of water is bound to
four of its neighbors. In liquid,
water molecules are constantly
bonding and re-bonding so space is
always changing
The lower density of ice is what
allows icebergs to float. In cold
climates, ice floats on top of the
water in lakes. This allows lake
animals such as fish to survive
the winter by staying in the
liquid water under the ice.
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