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THE WATER MOLECULE
Notes
Page 15 of INB
GET TO KNOW H 20
- 2 parts Hydrogen
- 1 part Oxygen
- Hydrogens have a positive
charge
- Oxygen has a negative
charge
ATOMS AND ELECTRON SHELLS
- Atoms are made up of protons,
neutrons, and electrons
- Protons and neutrons can be
found in the nucleus
- Electrons can be found around
the nucleus, in shells
- Each shell layer has a different
number of electrons it can hold
- In order to be stable (happy), the
atom must have a full outermost
shell.
ELECTRON DOT STRUCTURES: H AND O
Hydrogen has 1 electron floating
around its nucleus, but it needs 2 to
be stable.
- Oxygen has 8 electrons floating
around its nucleus.
- 6 of those electrons are in its
outermost electron shell. It needs 8 in its
outermost electron shell to be stable.
COVALENT BONDS
- Hydrogen
and Oxygen connect with one another through a
covalent bond. This means they share their electrons to make
each atom have a full outermost shell and be stable (happy)
POLAR MOLECULE
- The
angle of the water molecule’s bonds is
approximately 105 degrees – this makes water a
“bent molecule” or “angular molecule.”
- Because of where the electrons lay within the
bent molecule, water is polar. This means it has a
negative side and a positive side.
- All of the electrons (which have a negative
charge) are gathered around the oxygen, so the
oxygen side is negative.
- The hydrogen side is free of electrons, so it is
positive.
WHY DOES IT MATTER?
- Because
water has a positive end and a
negative end, it is drawn to other water
molecules.
- This means that water sticks together
through weak positive-negative connections.
These connections are called hydrogen
bonds.
- It also means water sticks to other
molecules and can pull them apart. This is
why many things dissolve so easily in water
– it is a universal solvent (a liquid things
called solutes dissolve in)
COHESION, ADHESION, AND SOLUBILITY
Cohesion – the ability of water molecules to
stick to one another
Ex. water in the glass
Adhesion – the ability of water molecules
to stick to other molecules
Ex. condensation on the glass
Solubility – the ability of water (or any
other solvent) to dissolve another material
(called a solute)
Ex. sugar dissolved in the ice tea
SURFACE TENSION
- Water molecules want to cling to each other
(cohesion).
- At the surface, however, there are fewer water
molecules to cling to since there is air above.
- This results in a stronger bond between those
molecules that actually do come in contact with
one another, and a layer of strongly bonded
water This surface layer is held together by
surface tension and creates a considerable
barrier between the atmosphere and the water.
- Other than mercury, water has the greatest
surface tension of any liquid.
BUOYANCY IS DIFFERENT THAN SURFACE TENSION
- Buoyancy or the ability of something to
float in water is different than surface
tension.
- Buoyancy results from the upward force
of the water opposing the downward
force of the weight of the object
attempting to float.
- You will learn more about buoyancy in
Marine Science II.
- Hint: it has to do with displacing water!
KEY POINTS: THE WATER MOLECULE
- Water is a covalent molecule made of two hydrogens and one oxygen
sharing electrons.
- Because of the uneven distribution of the electrons, water molecules have a
negative side and a positive side, making water a polar molecule.
- Polar molecules stick to one another through hydrogen bonding. When
water sticks to itself, it is called cohesion. Cohesion at the surface creates
surface tension, which allows some things to float at the top of the water.
- Polar molecules also pull apart other molecules. This is why salt, sugar, and
other materials dissolve so well in water. Water is called a universal
solvent.