Water is a Polar Molecule The polar nature of water molecules causes the molecules to attract each other. Like weak magnets, a positive pole (hydrogen) on each water molelcule attracts the negative pole (oxygen) This attraction causes molecules to form temporary bonds. These bonds form and break easily, and help water to stick together.
Water being a Polar Molecule causes it to have many unique properties.
A force that causes the tightness across the surface of water Caused by polar molecules Examples –water strider walking on water –raindrops beading on car windshield
Adhesion – is the attractive force between two different substances that are in contact with each other. Because of their shape, water molecules are attracted to other substances - Ex: Band-Aids Ex: Drops of water left on your skin after a swim
. Cohesion - the force that holds molecules of a single material together Because of their shape water molecules are attracted to one another. Water forms “drops” because of cohesion. Cohesion is responsible for clouds forming in the atmosphere (drops attract drops)
We see evidence of adhesion and cohesion and surface tension every day. Here’s an example.
Molecules in Motion Candy – roll it around Molecules in motion Dissolving Solute Solvent Solution Leads us to another Property of Water
Universal Solvent Solute – the dissolved substance – Candy Solvent – liquid capable of dissolving - Saliva Solution – a substance dissolved in water – the substance after the candy has dissolved with your saliva Water is called the Universal Solvent because it can dissolve more substances than any other known substance. Most substances dissolve in WATER
Density – the amount of mass per volume in a given substance D=m/v Different of Different Substances Density of water is 1g/cm 3 Ice – 0.92g/cm 3 Oil – 0.8 g/cm 3 Aluminum – 2.7 g/cm 3 Iron – 7.87 g/cm 3 Glass – 2.6 g/cm 3 Oak (wood)– 0.7 g/cm 3 Dogwood – 0.75 g/cm 3
Why Ice Floats 1. When water cools, the molecules line up in a grid like crystal structure 2. The molecules take up more space as ice than it did in liquid form Therefore, ice is less dense than liquid water Density of water is 1g/cm 3 It has buoyancy - the ability to float
Picture of Gridlock Structure that enables ICE to float.
Ice Floating Important for fish and other organisms that live in water. WHY? When lakes and ponds freeze in winter, the ice stays at the top. The fish are able to live in the water below the ice and find food on the bottom of the lake. If ice acted as most substances do when they freeze, the ice would sink to the bottom of the lake as it formed. Oh no!! What would happen to the “TURTLES”!!
Review: Density of Water Density of water = 1g/cm 3 Water becomes less dense when it becomes a solid. Reason: Due to the water molecules grid-like structure; ice is less dense than water **Water is actually most dense at 4 0 C
If the buoyant force is greater than or equal to the weight of the object, than it will float
Specific Heat - continued Water requires a lot of heat to increase its temperature Water has a high specific heat due to the many attractions among water molecules Effect: –Land has less dramatic temperature changes –Air is warmer inland than on the coast –Water remains warm and keeps the air above it warmer than the air over the cold land
Water and Land - different temperatures because of Specific Heat
Specific Heat Another Property of Water The amount of heat needed to raise the temperature of one gram of a substance by one degree Celsius. Substance Gold Silver Iron Air Wood Olive Oil Water Specific Heat (cal/g C). 03.06.11.24.44.47 1.0
Properties of Water Many are due to it’s Polar Structure One Negative Oxygen atom + 2 Positive Hydrogen atoms = Surface Tension Adhesion – cohesion – capillary action Universal solvent Ice floats Condensation – Evaporation Specific Heat Density of water – 1g/cm 3 H2OH2O
Standardized Test Practice Question 1 A water molecule is composed of which of the following ? A. one hydrogen atom and an oxygen atom B. one hydrogen atom and two oxygen atoms C. three oxygen atoms and one hydrogen atom D. two hydrogen atoms and one oxygen atom NC: 3.01
Standardized Test Practice The answer is D. Water is composed of two hydrogen atoms bonded to one oxygen atom. It is called a “polar molecule ” NC: 3.01
Question 2. Water has a ________ and ________ end making it a polar molecule. Because of its polarity, water can dissolve other substances. Because of the polarity of the water molecule, ice will _______ on water. NC: 3.01 positive negative float
Question 3 What property of water causes water to stick to other water molecules? NC: 3.01
Cohesion is the attraction between water molecules. It helps keep water liquid at room temperature and allows water to form into drops. NC: 3.01
Standardized Test Practice Question 4 During which process does water cycle from Earth’s surface to the atmosphere? A. condensation B. evaporation C. infiltration D. precipitation
Standardized Test Practice The answer is B. Water evaporates from Earth’s surface and enters the atmosphere as water vapor.
Standardized Test Practice Question 5 The attraction between water molecules is called ________. A. aquifer B. cohesion C. density D. specific heat NC: 3.01
Standardized Test Practice The answer is B. Cohesion is the attraction between water molecules that allows water to form droplets. NC: 3.01
Know more than just the definition. Understand how to apply the term! Properties of Water Polar Molecule Cohesion Adhesion Capillary Action Universal Solvent Why ice floats Density of water Buoyancy Specific Heat
Penny Predictions Independent Variable- The part of the experiment that you changed. Dependent Variable - The part of the experiment that changed as a result of what you changed. Controlled Variables: What stayed the same?
Penny Predictions What caused the water drops to be different (greater) than your predictions? (3or 4 reasons) If you had made the first prediction (penny) and then tested it, would you have been able to more accurately predict how many drops a nickel would hold? Is there a property of water that would explain the coins being able to hold so many drops?
COACH – properties of water Textbook – has some information Textbook –141- universal solvent 139 - density –140 – polar water molecule 140- cohesion –153 - water cycle 151 aquifer –142 - specific heat151 - groundwater
Know more than just the definition. Understand how to apply the term! Structure of the Hydrosphere Water Cycle Groundwater Distribution of Water Reservoirs Hydrosphere River Basins Salinity Properties of Water Polar Molecule Cohesion Adhesion Capillary Action Universal Solvent Why ice floats Density of water Buoyancy Specific Heat