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2. 2 Review of Water Basics 1.What is the chemical formula for water? Polarity H2OH2O Note: Hydrogen atoms and oxygen atoms are not red or white in real life!! Note: It is impossible to see a single water molecule with the naked eye or even with the most powerful light microscope.

3. 3 Water Basics 2. Water has ________ shared pairs and ________ unshared pairs. Therefore, water’s hybridization is ______and its molecular geometry is ___________. Polarity 2 2 sp 3 bent

4. 4 Polarity of Water 3. Label: Hydrogen (2) Oxygen (1) Note: A hydrogen atom has a partial positive charge. Label it. ( ) Note: An oxygen atom has a partial negative charge. Label it. ( ) Polarity Hydrogen Oxygen

5. 5 Background - Polar Nature of Water Oxygen has 6 valence (outer) electrons needs 8 to have a full outer shell. Hydrogen has 1 valence electron needs 2 to have a full outer shell. Neither atom wants to give up electrons. Instead, they share electrons to form covalent bonds. Polarity Hydrogen Oxygen

6. 6 Background - Polar Nature of Water Although they are sharing electrons with the hydrogen atoms, the oxygen atom has a greater attraction for the electrons. So, the electrons spend more time near oxygen’s end of the molecule. Polarity Hydrogen Oxygen

7. 7 Background - Polar Nature of Water Oxygen atom also has two unshared pairs of electrons These tend to make the oxygen end of the molecule more negative. Unshared pairs repel the shared pairs and hydrogen atoms off to one side, creating the familiar Mickey Mouse appearance of the water molecule. Polarity Hydrogen Oxygen

8. 8 Background - Polar Nature of Water As a result, the oxygen end of water tends to have a slight (partial) negative charge, while the hydrogen end of water tends to have a slight (partial) positive charge 4. Since water has positive and negative poles, it is a polar molecule. Also, the oxygen is highly electronegative. Polarity Hydrogen Oxygen

9. 9 Polar Molecules 5. Molecules such as water that have positive and negative ends are called __________ molecules. (and those positive and negative “ends” are called dipoles.) Polarity polar

10. 10 Polarity 6.What do you think will happen when two water molecules bump into each other? Take the water molecules from the kit and “bump” them into each other. Polarity What ends “stuck” to each other when you bumped them together?

11. 11 Polarity In reality water acts just like the magnets inside our models. The positive end of one water molecule will bond to the negative end of another water molecule. Polarity 7. Take some water molecules from your water kit and see how many hydrogen bonds each water molecule can form.

12. 12 Hydrogen Bonding 8. Allow 2 water molecules to stick together. Pull the two water molecules apart. Try to pull a hydrogen atom off one of the water molecules. Which is harder to do? Hydrogen Bonding

13. 13 Hydrogen and Covalent Bonding 9. What is the name for the intermolecular force (between the molecules) that holds these two water molecules together? Hydrogen Bonding Hydrogen bonding

14. 14 Hydrogen and Covalent Bonding 10. What is the name for the intramolecular bond (inside the water molecule) that holds the hydrogen atoms and oxygen atom within the water molecule? 11. Which bond is stronger? Hydrogen Bonding Polar Covalent bonding Covalent bonding

15. Special Properties of Water Water’s ability to hydrogen bond gives water all of these special properties: high surface tension, low vapor pressure and high boiling point, solid state is less dense than liquid state, high specific heat, universal solvent

16. High Surface Tension an inward force that tends to minimize the surface area of a liquid; it causes the surface to behave as if it were a thin skin. Example: glass of water bulges over the top, water forms round drops and water on greasy surface All of this occurs because water hydrogen bonds.

17. Surface Tension of Water metal paper clip on waterwater forms “beads”

18. Surface Tension One water molecule hydrogen bonds to another. Also, hydrogen bonding occurs to other molecules all around. Each water molecule can hydrogen bond to four other water molecules. H H O ++ ++ -- H H O ++ -- ++

19. Surface Tension A water molecule in the middle of solution is pulled in all directions.

20. Surface Tension Not true at the surface. Only pulled down and to each side. Holds the molecules together. Causes surface tension.

21. Surface Tension Water drops are round, because all molecules on the edge are pulled to the middle- not to the air!

22. Surface Tension Glass has polar molecules. Glass can hydrogen bond. Attracts the water molecules. Some of the pull is up a cylinder.

23. Meniscus Water curves up along the side of glass. This makes the meniscus, as in a graduated cylinder Plastics are non- wetting; no attraction

24. Meniscus In Glass In Plastic A meniscus is the curved surface that occurs when you put water in a container like a test tube or a beaker.

25. Surface tension All liquids have surface tension –water is higher than most others How to decrease surface tension? –Use a surfactant - surface active agent –It is a wetting agent, like detergent or soap that interferes with hydrogen bonding

26. Surfactants Surfactants lower the surface tension of water by breaking the hydrogen bonds of water, essentially making it 'wetter' so that it is less likely to stick to itself and more likely to interact with oil and grease. Basically, soap allows oil and water to mix so that oily grime can be removed during rinsing.

27. Low vapor pressure and high ___________ _______ : means water needs a lot of energy/heat to make it evaporate or __________. Low Vapor Pressure boiling point boil l good thing water has a low vapor pressure or lakes and oceans would evaporate very quickly!

28. Ice Most liquids contract (get smaller) as they are cooled. They get more dense. When they change to solid, they are more dense than the liquid. Example solid metals sink in liquid metal. –But, ice floats in water. Why?

29. Ice The density of ice is 0.9167 g/cm³ at 0°C, whereas water has a density of 1.0 g/cm³density becomes more dense as it cools until it reaches maximum density at 4ºC. Then it becomes less dense. As the molecules slow down, they arrange themselves into honeycomb shaped crystals that are held together by hydrogen bonds. Now take your water molecules and arrange them into a honeycomb shape.

30. Why is ice floating on water important to life on earth? 30

31. Specific Heat Capacity Water has a high heat capacity (also called specific heat). Occurs because of hydrogen bonding of water. Specific heat is the amount of energy needed to raise the temperature of a substance by 1°C. The specific heat of water is 1 calorie/gram °C or 4.186 joule/gram °C which is higher than any other common substance. Metals get hot or cold really fast.

32. Lucky for me, you, and our fish in the pond, water does indeed have a very high specific heat capacity. The specific heat of water is the amount of heat needed to change water from a solid to a liquid or a liquid to a gas. It doesn’t get hot very fast or cold very fast! 32 Specific Heat Capacity

33. 33 Non-Polar Molecules The chemical formula of ethane is ( C _ _ H __ ) The gray molecule in your kit is ethane. Which color is the carbon and which color is the hydrogen on the ethane? Hydrogen Bonding 26

34. 34 Non-Polar Molecules Will ethane form a hydrogen bond with water? Hydrogen Bonding Try and “stick” the water and ethane together.

35. 35 Non-Polar Molecules Is ethane a polar molecule or a non-polar molecule? Look at the structure below. Hydrogen Bonding Non-polar

36. 36 Ionic Compounds This is sodium chloride. What do the colors represent? Can the blue ball and green ball connect at more than one spot? What is the chemical formula of sodium chloride? Hydrogen Bonding NaCl

37. 37 Ionic Bonds This positive / negative attraction between ions is called an ________ bond. Hydrogen Bonding ionic Try and pull the sodium and chlorine apart. It is harder to pull two water molecules apart or sodium and chlorine apart?

38. 38 Ionic Bonds and Polar Molecules “Dissolve” sodium chloride in water by surrounding each ion with water molecules. Which end of the water is attracted to sodium? Which end of the water is attracted to chloride? Hydrogen Bonding

39. 39 Ionic Bonds Are chloride ions positively or negatively charged? How do you know? Hydrogen Bonding

40. 40 Ionic Bonds Are sodium ions positively or negatively charged? How do you know? Hydrogen Bonding

41. 41 Ions and Nonpolar compounds Ethane is non-polar. Do sodium or chloride interact with ethane? Would sodium chloride dissolve in a nonpolar liquid like ethane or oil? Hydrogen Bonding

42. 42 Water - Universal Solvent Because of its polar nature, water is called the universal ________________. It can dissolve all ionic and polar covalent compounds. It dissolves more substances than any other liquid. Hydrogen Bonding solvent

43. Adhesion and Cohesion The attraction between two like molecules is cohesion. The attraction between two unlike molecules is adhesion. 43

44. Capillary Action 44 Capillary action occurs because water is sticky, thanks to the forces of cohesion (water molecules like to stay close together) and adhesion (water molecules are attracted and stick to other substances).

45. Capillary Action Plants and trees couldn't thrive without capillary action. Plants put down roots into the soil which are capable of carrying water from the soil up into the plant. Now try capillary action with your water molecules from the water kit. 45

46. Hydrophobic & Hydrophilic 'hydrophilic' means that it likes water, and that water will 'wet' the surface. If you put water on a paper towel, it will rapidly wet the fibers in the towel and spread out. 46 'hydrophobic' means that it repels water. This is why water droplets shrink up tightly to form beads as they are repelled by the hydrophobic waxy coat of a newly waxed car. Wax and oils are hydrophobic.