Transcript The Properties of WATER

What is so special about water?
 It is the most abundant compound in most living
things
 Water is the only compound that exists in all 3 phases
(solid, liquid and gas)on Earth
 Water expands as it freezes; thus, ice is less dense than
liquid water which allows it to float on the surfaces of
lakes and rivers
Thinking cap time…..
 With your partner, discuss the
following: why is the fact that ice floats
on water (remember, ice is less dense
than water) essential to much of life on
Earth?
 Time: One minute
The Chemical Makeup of H20
 Water is bonded covalently
 The Hydrogen atoms are not bonded together; they are
each bonded to the Oxygen atom
 In a water molecule, the electrons are shared
unequally. They tend to hover around the Oxygen
atom
Polarity
 Oxygen atoms have a much stronger attraction for
electrons than do Hydrogen atoms; thus there is a
greater probability of finding the shared electrons near
the oxygen atom
 This results in the Oxygen end of the water molecule
having a slightly negative charge and the Hydrogen
end having a slightly positive charge
 Polarity refers to this uneven distribution of
charge(electrons) within a molecule
Hydrogen Bonds
 Because water molecules are polar (slightly negative
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and positive ends)they can attract each other
A hydrogen atom in one water molecule is attracted to
the oxygen atom of another water molecule
This is referred to as Hydrogen Bonding
Hydrogen bonds are not as strong as covalent or ionic
bonds
This type of bonding accounts for the many unique
properties of water
A Hydrogen Bond
Think-Pair-Share
 THINK: On your own, write down why you think
Hydrogen bonds would not be as strong as ionic or
covalent bonds
 PAIR: discuss and compare answers with your partner
 SHARE: be prepared to discuss as a class
 TIME: 2 minutes
Cohesion
 Cohesion is an attraction between molecules of the
same substance
 Because of hydrogen bonding, water is very cohesive
 Waters cohesion causes molecules on the surface of
water to be drawn inward, which is why drops of water
form beads on a smooth surface
Cohesion and Surface Tension
 The cohesive property of water explains why some
insects and spiders can walk on the surface of water
 Surface Tension: the strong attraction between
molecules of water creates a force which acts like a film
and can support very light objects
Adhesion
 Adhesion is the attraction between molecules of different
substances (review: what was cohesion?)
 Have you ever been asked to read the volume in a
graduated cylinder at eye level? The surface of the water
dips slightly in the center because the adhesion between
the water molecules and the glass molecules is stronger
than the cohesion between water molecules
Check for Understanding
With your partner, summarize
what cohesion and adhesion are
Come up with a clever way to not
get the two confused
TIME: 2 minutes
Cohesion, Adhesion
and Capillary Action
 Capillary Action is the force that draws water out of
the roots of plants and up into its stems and leaves
 Adhesion between the water molecules and the
root/stem walls causes water to pull up the sides
 Cohesion between water molecules holds the column
of water together as it rises
 Cohesion and adhesion work together to allow for
capillary action
Water as a Mixture
 Water is not always pure; it is often found as part of a
mixture
 A mixture is a material composed of two or more elements
or compounds that are physically mixed together but not
chemically combined
 Two different mixtures that can be made with water:
 Solution: all of the components are evenly distributed (ie.
Salt in water- the water serves as the solvent and salt is the
solute)
 Suspension: when materials do not dissolve in water but
form small pieces (clumps) to do not settle (ie. Sand in water)