Primarily due to polarity

Properties of Water

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

*Intro to WaterWater 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 lessonVideo 2

Polarity Hydrogen bondCohesionAdhesionSurface tensionCapillary actionSpecific 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 magnetVideo 4

Lewis e-dot structure of water molecule2 lone pairs – accounts for its bent shape

Water molecule is V-shaped - BENT

Thinking critically - 5Video 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)

H2O is Polar

•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.

Water is Polar

Blast from the past:

•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-polarOxygen – 3.44Hydrogen – 2.20Difference in values– 1.24 (polar bond) The bond is polar if the difference is between 0.5 - 1.7.Non-polar = or less than 0.5Ionic = or greater than 1.7

Other examples of polar molecules

(no lone pairs):

Carbon is more electronegative

Oxygen is more electronegative

*Non-polar molecule

(lone pair):

Water is a universal solvent

•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.

“Like dissolves like”(due to its polarity)

Water (polar) + Styrofoam (non-polar)

Acetone (nonpolar) + Styrofoam (non-polar)

Polar Bonding

•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

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

Forces due to polarity

• 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

Surface Tension

•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 tensionThere the water behaves like an flexible sheet allowing denser objects to “sit” on the surface.

Surface tension (cohesion)

•Can be seen as water droplets form

•Helps insects walk across water

Adhesion•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.

*Adhesion

*Can be seen as water droplets form on the spider web (another polar surface)

Form spheres & hold onto plant leaves

*Capillary action

*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)Polarity-Like dissolves like-Heat capacityWater acts as a magnet-Trade notebooks with your partner write one constructive comment in your partner’s notebook. Hand them back their notebook( 1min)

Warm up: 2/25/13

• 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.swf

• 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 ionsb.Ions for ionic and molecules for covalent

compoundsc.Ions for covalent and molecules for ionic

Checking for understanding

The dissolution of KNO3 and C3H6O (acetone) in water occurs:a.Molecules by molecules for both KNO3 and

C3H6Ob.Ion by ion for KNO3 and molecule by

molecule for C3H6Oc.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