Review of Water Basics

2. Review of Water Basics • What is the chemical formula for water? H2O Polarity

3. Water Basics 2. On your paper, write which elements the H and the O represent in the chemical formula for water. • 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. Polarity

4. Water Basics 3. The 2 in H2O means there are two __________ atoms. 4. How many oxygen atoms does water contain? ____ • (Why doesn’t O need a subscript??) Polarity

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. Hydrogen Hydrogen Oxygen Polarity

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

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

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 Since water has positive and negative poles, it is a polar molecule. Hydrogen Hydrogen Oxygen Polarity

9. Polarity of Water 5. 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. ( ) Hydrogen Hydrogen Oxygen Polarity

10. Polarity 6. What do you think will happen when two water molecules bump into each other? • Write your prediction on Q. 6 on your lab paper. Polarity

11. Polarity 7. Hold 3 or 4 water molecules in your hands. Roll them around between your palms. Do the water molecules stick together? 7. What happens when you stop rolling - do they stick together now? Polarity

12. Polarity • Experiment with 2 water molecule models: • Think about what you have discovered, then answer questions 8 & 9. • (see next slide) Polarity

13. Polarity 9. What are the similarities and difference between magnets and water molecules? • Use a Venn diagram to show your answer. similarities Polarity

14. 10. Water Drop Trivia!! 10. How many water molecules are in a single drop of water? • Answer: • 3,000,000,000,000,000,000,000 • Or 3 x 1021 molecules • A “water drop” made of 3 x 1021 of the 3D Water Molecule Models would be larger than the earth. • Record this fact on your lab paper. Polarity

15. Polar Molecules 11. Molecules such as water that have positive and negative ends are called __________ molecules. (and those positive and negative “ends” are called dipoles.) polar Polarity

16. Hydrogen Bonding 12. Allow the 2 water molecules to stick together. • Pull the two water molecules apart. • Try to pull a hydrogen atom off one of the water molecules. • On Question 11, circle the easier choice. Hydrogen Bonding

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

18. Hydrogen and Covalent Bonding 14. What is the name for the intramolecular bond (inside the water molecule) that holds the hydrogen atoms and oxygen atom within the water molecule? 15. Which bond is stronger? Covalent bonding Covalent bonding Hydrogen Bonding

19. Non-Polar Molecules 16. The gray molecule is ethane. What do the different colors on the ethane molecule represent? What is the chemical formula of ethane? ( C__H__ ) 2 6 Hydrogen Bonding

20. Non-Polar Molecules 17. Will ethane form a hydrogen bond with water? Hydrogen Bonding

21. Non-Polar Molecules 18. Is ethane a polar molecule or a non-polar molecule? Non-polar Hydrogen Bonding

22. Ionic Compounds • This is sodium chloride. • What do the colors represent? 19. Can the blue ball and green ball connect at more than one spot? What is the chemical formula of sodium chloride? NaCl Hydrogen Bonding

23. Ionic Bonds 20. This positive / negative attraction between ions is called an ________ bond. ionic Hydrogen Bonding

24. Ionic Bonds and Polar Molecules • “Dissolve” sodium chloride in water by surrounding each ion with water molecules. 21. Which end of the water is attracted to sodium? Which end of the water is attracted to chloride? Hydrogen Bonding

25. Ionic Bonds 22. Are chloride ions positively or negatively charged? 23. How do you know? Hydrogen Bonding

26. Ionic Bonds 24. Are sodium ions positively or negatively charged? 25. How do you know? Hydrogen Bonding

27. Ions and Nonpolar compounds Ethane is non-polar. 26. Do sodium or chloride interact with ethane? 27. Would sodium chloride dissolve in a nonpolar liquid? Hydrogen Bonding

28. Water - Universal Solvent 28. Because of its polar nature, water is called the universal ________________. It can dissolve all ionic and polar covalent compounds. solvent Hydrogen Bonding

29. “In-Betweeners” • Disconnect the two halves of the ethane molecule to make 2 methanes (CH4). • Add an (OH)- group to the methane to make methanol. (wood alcohol) • 29. What is the chemical formula of methanol? CH3OH Hydrogen Bonding

30. Hydrogen Bonding - Bonus BB When methanol and water interact, the water is attracted to: The (OH)- group Hydrogen Bonding

31. Hydrogen Bonding - Bonus 2 BB2: Na and Cl will interact with (stick to) ethanol (C2H5OH). However, would ethanol molecules be able to easily surround and “cage” the Na and Cl ions the way that water molecules can? NaCl Ethanol Hydrogen Bonding