Properties of Water
Primarily due to polarity
Video1 “Properties of water” – 4 ½ min
•Why is ice less dense than water?
•How does ice floating on water impact the
survival of the living organisms
•Draw the water structure.
•How does the term “polar” describe the water
molecule?
•What is the intermolecular force between
water molecules called?
•Explain surface tension in water
Intro to water
•Molecule
•two hydrogen atoms and one oxygen atom
•v-shaped triangular molecule
•hydrogen bonds
•Polarity
•properties
*
Water is a molecule made up of two hydrogen
atoms and one oxygen atom. It has the formula
H2O. When oxygen and hydrogen combine (H-O-H)
they form a v-shaped triangular molecule. While
water molecules are electrically neutral, the
oxygen atom holds a small negative charge and the
two hydrogen atoms hold small positive charges.
Water molecules are attracted to each other,
creating hydrogen bonds. These bonds determine
almost every physical property of water and many
of its chemical properties too. Scientists believe
this unusual electrical balancing, called polarity,
gives water some of its remarkable properties
* Terms to know by the end of the lesson
Video 2
Polarity
Hydrogen bond
Cohesion
Adhesion
Surface tension
Capillary action
Specific heat
Water Physical Properties (review)
•At what temperature in Celsius does water
start boiling?
•At what temperature in Celsius does water
start melting?
•At what temperature in Celsius does water
start freezing?
•What is the density of water?
Water has a high specific heat capacity
• Water has the ability to absorb a lot of heat with a
relatively small increase in temperature
• Water has one of the highest specific heat capacity
This allows marine organisms to avoid drastic
temperature fluctuations in the seawater.
This allows orchards grown on the coast to
survive hot summers and severe winters.
http://www.youtube.com/watch?v=qeDZQ9-gsjY
Water “acts” like a magnet
Video 4
Lewis e-dot structure of water molecule
2 lone pairs – accounts for its bent shape
Water molecule is
V-shaped - BENT
Thinking critically - 5
Video 6
If matter expands when heated,
and contracts when cooled, why
does ice expand (increase in
volume) when water freezes?
When water freezes, it goes from a mixed up liquid
state where all these V's are just sliding around
each other, to an ordered crystalline solid state
where all the V's have to connect with each other
in nice orderly solid shapes.
The closest and easiest solid crystal shape for something that exists
as a 104.5 degree V is a hexagonal (really tetrahedral in 3D) crystal.
Think of it as a flat hexagonal snowflake shape, but it really goes in
three dimensions. The water molecules want to do this because to
them it "feels" nicer--that is: they feel less strain and they can get
into a lower energy state by getting into this nice orderly
hexagonal crystal.
video clip “Why ice float “
Critical Thinking:
If ice were more dense than liquid water, how
would this impact the survival of the marine
life?
(The floating layer of ice insulates the liquid
water below, so that it wouldn’t freeze – this
makes the ocean environment to easier to live
in)
•As we know – water is neutral
(equal number of e- & p+ = zero Net Charge)
•But because the O atom is more
electronegative than the H atoms – electrons
spend more of their time nearer the oxygen.
(O atom attracts more than its “fair” share”
of electrons).
•This gives water a slight overall charge.
The oxygen end “acts” negative.
The hydrogen end “acts” positive.
•This charge is called polarity
Oxygen “pulls” closer to it creating
positive and negative sides of the
polar molecule.
•What is electronegativity?
•How does it change across a period?
•Down a group?
•What is the most electronegative element on
the PT?
•Least electronegative?
•Which of the two elements, S or N, has a
greater ability to attract another atom’s
valence electrons?
I am more electronegative than selenium, but
less electronegative than chlorine?
Who am I?
Electronegativity values-how to determine if a
bond is polar or not-polar
Other examples of polar
molecules
(no lone pairs
Carbon is more
electronegative
Oxygen is more
electronegative
*
•Water can dissolve more substances than any
other solvent.
•Give examples of substances that water can
dissolve.
•The dissolving power of water is very important
for life on Earth. Wherever water goes, it carries
dissolved chemicals, minerals, and nutrients that
are used to support living things.
Water (polar) + Styrofoam (non-polar)
Acetone (nonpolar) + Styrofoam (nonpolar)
“Like dissolves like”
(due to its polarity)
•Polarity really does allow bonding
•They are hydrogen bonds and they
are weak
•They last for fractions of a second
•Continuously break and reform
video clip “Water molecule Part 1”
- bonds breaking and reforming
Polar Bonding
Hydrogen Bonds
(Formed between a highly Electronegative atom of a
polar molecule and a hydrogen
(O-H)
Opposites
attract
This model to show the attraction
between H and O – hydrogen bonding
•
•
Cohesion
Adhesion
Cohesion
(water is sticky)
Attraction between particles of the same
substance ( why water is attracted to itself)
•Results in Surface tension (a measure of the
strength of water’s surface)
Produces a surface film on water that allows
insects to walk on the surface of water
•Inside a drop of water polar water molecules
attract to each other in a random fashion
•At the surface of the drop, water does not
attract to the air
•A unified layer of molecules at the surface
creates surface tension
There the water behaves like an flexible sheet
allowing denser objects to “sit” on the
surface.
Surface Tension
• Can be seen as water
droplets form
• Helps insects walk across
water
Surface tension
(cohesion)
•Attraction between two different
substances.
•Water will form hydrogen bonds with
other surfaces such as glass, soil, plant
tissues, and cotton
•Adhesion Causes Capillary Action, which
gives water the ability to “climb”
structures.
* Can be seen as water droplets
form on the spider web
(another polar surface)
Form spheres & hold onto
plant leaves
*
*
* We know that gravity is ALWAYS pulling on objects with
mass
* Yet water can move up a paper towel with relative ease
– How can this happen?
* Because the positive and negative charges in the paper
attract the polar water molecules (adhesion)
* This property of adhesion is called capillary action.
Explain the following water properties in both
words and drawings(2 min)
PolarityLike dissolves likeHeat capacity
Water acts as a magnetTrade notebooks with your partner write one
constructive comment in your partner’s
notebook. Hand them back their notebook(
1min)
•
How do heterogeneous and homogeneous mixtures differ?(Left Side)
Salt solution and Oil in water
2 min - Quick Write: Based on your prior knowledge about mixtures, explain why a
salt solution is classified as a homogeneous mixture and a mixture of oil and water is
said to be a heterogeneous mixture.
White boards activity:
Homo- or Hetero - ?
COKE
AIR
STEEL
A JAR OF PENNIES
Coke (mixture of CO2 gas, water, sugar, caramel color, food flavorings)
Air (mixture of O2 and N2)
Steel (alloy – mixture of Fe and C)
A jar of pennies and nickels
• Notes
By the end of the day you will know:
• Solute
• Solvent
• Solution
• Soluble
• Insoluble
• Immiscible
• Separation
• Solvation
• Factors affecting the rate of dissolution
Next notes…
Complete the sentences.
When you put salt into water it______. The salt dissolves
because it is ________in the water. The substance which
dissolves is called the ______. The substance that does the
dissolving is called the _______. When something dissolves
you get a _______.
Water is a ________. Salt is a ________.
When a substance does not dissolve it is________
Dissolution of salt in water
* http://www.nsf.gov/news/special_reports/chemistrynow/chem
_water.jsp
• Animation - Dissolution of an Ionic compound (results in
dissociation) and a covalent compound (no dissociation)
http://www.chem.ufl.edu/~itl/4411/react/dissolution_of_cmpds.s
wf
• Animation – Strong electrolyte (complete dissociation into ions) –
many ionic compounds – conduct electricity - (+ strong acids and
bases – will cover in more detail in Bundle 11)
http://www.chem.ufl.edu/~itl/4411/react/04M05AN1.MOV
• Animation – Weak electrolyte (partial dissociation) – weak acids
and bases (if a conductivity meter is used - light is not as bright
(dim) compared to a strong electrolyte)
http://www.chem.ufl.edu/~itl/4411/react/04M05AN2.MOV
• Animation – Non-electrolyte ( no dissociation)
- no disruption of
its molecular (covalent) structure – does not conduct electricity
http://www.chem.ufl.edu/~itl/4411/react/04M05AN3.MOV
The dissolved components of ionic and
covalent compounds are:
a.All ions
b.Ions for ionic and molecules for covalent
compounds
c.Ions for covalent and molecules for ionic
The dissolution of KNO3 and C3H6O (acetone)
in water occurs:
a.Molecules by molecules for both KNO3 and
C3H6O
b.Ion by ion for KNO3 and molecule by
molecule for C3H6O
c.Ion by ion for C3H6O and molecule by
molecule for KNO3
Based on your observations of the dissolution process on
the animation, how do you think substances get
dissolved?
a.Each solvent molecules gets separated from other
molecules and is surrounded by ions in ionic substances
or molecules in covalent substances
b.Each ion in covalent substances and each molecule in
ionic substances gets separated from other molecules
or ions and is surrounded by solvent molecules
c. Each ion in ionic substances and each molecule in
covalent substances gets separated from other
molecules or ions and is surrounded by solvent
molecules.
Factors that Affect the Rate of
Dissolution
Pre-assessment:
If you wanted to dissolve a substance
in water as quickly as possible what
could you do?
The three methods to increase
the rate of dissolving for a
solid are?
•Heat it!
•Crush it!
•Stir it!
The Great Soda Mystery!
1. What is the difference
between the hot soda and
cold soda? Why?
2. As temperature _______,
solubility of a gas ______.
3. Does pressure affect the
amount of gas in the soda?
How?
4. As pressure _____,
solubility of gases ______.
•Solubility of a gas and
pressure on the solution
is a/an ____ proportion.
•Solubility of a solid in a
solvent is ____ changed
with increasing pressure.
•In general solubility of
solids increases with
increasing temperature.
•Solubility of gases in water
decreases with increasing
temperature.
* Day 3 -Solubility