Water. Water is the most essential and abundant substance on Earth. Cells are made up mostly of water and most cells are surrounded by water. The importance of water is largely due to its many unique characteristics, which all directly relate to one very important property of water.
Water is the most essential and abundant substance on Earth. Cells are made up mostly of water and most cells are surrounded by water. The importance of water is largely due to its many unique characteristics, which all directly relate to one very important property of water.
Polarity is the unequal sharing of electrons in molecules formed with covalent bonds
The chemical formula of water is ___________. The atomic number of hydrogen is ___ and the atomic number of oxygen is ___.
Therefore how many protons does the oxygen nucleus have?
How many protons does each hydrogen nucleus have?
Due to this difference, the oxygen nucleus has a much stronger positive charge than each hydrogen nucleus.
What type of bond forms a water molecule???
the shared negatively-charged electrons are much more attracted to oxygen (because of its greater positive charge).
This results in all 10 electrons
orbiting around the oxygen end
of the molecule just about all the
Therefore, the oxygen end of the molecule is slightly negative (due to the presence of all those electrons) and the hydrogen end of the molecule is slightly positive (due to the lack of the electrons).
A molecule in which the charges are unevenly distributed is called a polar molecule, because the molecule is like a magnet with poles.
Bonds that form between the_________ charged _____________
in one molecule and a
__________ charged _________
in a nearby molecule are called
Is a hydrogen bond a true chemical bond?
No- it does not result in the formation of a new compound- it is simply an attraction.
Hydrogen bond animation
Images from: http://www.estrellamountain.edu/faculty/farabee/biobk/BioBookCHEM2.html
The attraction between the Hydrogen atom on one water molecule and the oxygen atom on the other water molecule is an example of a hydrogen bond.
that is responsible for many of its special properties and characteristics.
Hydrogen bonds are not as strong as covalent or ionic bonds…
Multiple hydrogen bonds
A single water molecule may be involved with as many as ___ hydrogen bonds at the same time.
Properties of waterDue to water’s polarity, it has unique properties important in maintaining that forever important internal harmony we call… (everyone together!!!)
1. Water is “sticky”
2. High specific heat
3. High heat of vaporization
4. Expansion on freezing
5. Water as a Solvent
“Co” = “together” or “like”
“sion” = “stick”
The attraction between molecules of the same substance (why droplets of water form)
Due to formation of multiple hydrogen bonds
Contributes to the upward transport of water in plants- capillary action (roots shoots)
“Ad” = “unlike”
The attraction between molecules of different substances
Due to formation of multiple hydrogen bonds between polar water molecules and other slightly charged molecules
water on a penny; along with cohesion, contributes to capillary action (the ability of water to rise in a narrow tube against the force of gravity)
The measure of how difficult it is to stretch or break the surface of a liquid
Results from the H bonding of water molecules to one another at the surface and below the surface (cohesion)
Gives still water on a lake or pond the appearance of glass
Ex: insects walking on water
The amount of heat needed to raise the temp of 1 gram of water by 1 degree Celsius
Water has a very high specific heat- it takes a lot of energy to raise the temp of water
Crucial in temperature stability in living systems so that they can maintain homeostasis
Due to H bonding
A lot of heat energy is required to evaporate water (molecules that move fast enough can overcome their attraction to one another and depart the liquid and enter the air as gas)
When water does evaporate from a surface, it draws heat energy out from the layer beneath, creating a cooling effect.
This is called evaporative cooling
Ex: evaporation of sweat by a human; evaporation of water from leaves of plant (transpiration)
Water is one of the few substances that are less dense as a solid than as a liquid- therefore it floats.
While other materials contract when they solidify, water expands.
molecules at “arms length”-
far enough apart to make ice
10% less dense than liquid water.
(water’s density= 1.0 g/ml)
Water dissolves many substances due to its polarity.
Known as a very versatile solvent- other polar substances dissolve very easily in water.
Solvent- the dissolving agent
of a solution. Ex. Water
Solute- the substance that is
____________________ means “water loving”
_________ groups/molecules try to _________ and touch water or ______________ molecules
Water makes a great solvent in
living things because so many
molecules found in living things
are polar or have a charge.
“Like dissolves like”
_________________ means “water fearing”
___________ groups/molecules try to _________ other __________ molecules and __________ ________ molecules
Oil based paints dissolve
in solvents such as
. . . not water.
*Also known as water soluble
Examples of hydrophobic substances- oils, fats, lipids, waxes (non-polar compounds)
*Also known as water insoluble
______ works because it has a _____________ that dissolves _______ and a __________ that dissolves in _____ to wash away oily dirt.
Average person ~~ 60-70% water
Babies ~~ 78%
Human brain ~~90%
Image from: http://sjr.state.fl.us/programs/outreach/pubs/irl_update/images/water_glass.jpg
1. It’s __________ so it can ____________ lots of different substances.
2. It can _________ lots of ______
_______________________________ very much. (That helps with _________________)
3. ____________________ form between water
molecules so they stick together.
4.Water is an important ___________________
in many CHEMICAL REACTIONS.
WITHOUT changing temperature