Water Properties
What are the physical and chemical properties of water that make it so
unique and necessary for living things? When you look at water, taste and smell
it—well, what could be more boring? Pure water is virtually colorless and has no
taste or smell. But the hidden qualities of water make it a most interesting subject.
Water's Chemical Properties
You probably know water's chemical description is H20. As the diagram to the left
shows, that is one atom of oxygen bound to two atoms of hydroge n.
(If the water molecule here looks familiar, remember that everyone's
favorite mouse is mostly water, too). The hydrogen atoms are
"attached" to one side of the oxygen atom, resulting in a water
molecule having a positive charge on the side where the hydrogen
atoms are and a negative charge on the other side, where the oxygen atom is. A
compound with one negatively charged side and one positively
charged side is called a polar molecule.
Since opposite electrical charges attract, water molecules tend to
attract each other, making water kind of "sticky." As the right-side
diagram shows, the side with the hydrogen atoms (positive charge)
attracts the oxygen side (negative charge) of a different water
molecule.
All these water molecules attracting each other mean they tend to
clump toge ther. This is why wa ter drops a re, in fact, drop s! If it were n’t
for some of Earth's forces, such as gravity, a drop of water would be ball
shaped -a perfect sphere. Even if it doesn't form a perfect sphere on
Earth, we should be happy water is sticky.
Water is called the "universal solvent" because it dissolves more substances than
any other liquid. This means that wherever water goes, either through the ground
or through our bodies, it takes along valuable chemicals, minerals, and nutrients.
Pure water has a neutral pH of 7, which is neither acidic nor basic.
Water's Physical Properties
Water is unique in that it is the only natural substance that is found in all three
states -- liquid, solid (ice), and gas (steam) -- at the temperatures normally found
on Earth. Earth's water is constantly interacting, changing, and in movement.
Water freezes at 320 Fahrenheit (F) and boils at 2120 F (at sea level, but 186.4° at
14,000
feet). In fact, water's freezing and boiling points are the baseline with
which temperature is measured: 00 on the Celsius scale is water's freezing point,
and
100
0
is water's boiling point. Water is unusual in that the solid form, ice, is
less dense than the liquid form, which is why ice floats.
