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Today is Thursday, September 19 th , 2013

In This Lesson: Bonding (Lesson 4 of 9). Today is Thursday, September 19 th , 2013. Pre-Class: Answer one of these two questions: What is the capacity of each of the first three energy levels? What does “valence” mean (in chemistry)?. Today’s Agenda. Bonding Aww … :)

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Today is Thursday, September 19 th , 2013

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  1. In This Lesson: Bonding (Lesson 4 of 9) Today is Thursday,September 19th, 2013 Pre-Class: Answer one of these two questions: What is the capacity of each of the first three energy levels? What does “valence” mean (in chemistry)?

  2. Today’s Agenda • Bonding • Aww… :) • Forces sort of like bonding • Properties of water (the very basics) • Almost near the living stuff! • Where is this in my book? • P. 37-39

  3. Bonding • Bonding is what forms compounds. • Once a compound is formed and we write its chemical formula, we can see how many atoms of each element are in it: • H2O – 2 Hydrogen, 1 Oxygen • CO2 – 1 Carbon, 2 Oxygen • H2SO4 – 2 Hydrogen, 1 Sulfur, 4 Oxygen • C6H12O6 – 6 Carbon, 12 Hydrogen, 6 Oxygen

  4. Things We Know • After so much information recently, here’s some things we know, and that we’ll need for future information: • Ions are atoms out of balance. They either have greater or fewer electrons than “normal.” • Valence electrons are the ones located in the outermost energy level. • Atoms “want” to fill their valence shells, either by dropping extra electrons or adding more. • This makes them STABLE.

  5. Bonding • There are three main kinds of bonds we’ll talk about briefly in this class, and here they are: • Ionic • Covalent • Hydrogen • Plus one more thing that holds stuff together but really isn’t a bond.

  6. Bonding • Before we talk in detail about Ionic Bonding, let’s watch a short clip from NOVA about how the bonds work. • It’s a good overview for bonds in general.

  7. Bonding • Let’s start with Ionic Bonding. • Ionic bonding is when electrons are transferred from one atom to another. • Involves oppositely charged atoms. • Positive atom meets negative atom. • Example: Na+ plus Cl- = NaCl (salt) • Animation on next slide…

  8. BondsIonic How to remember: Ions are selfish

  9. Ionic Bonds • Sodium has 1 valence electron, Chlorine has 7. • Sodium is looking to lose an electron, Chlorine to gain an electron.

  10. Ionic Bonds • So Sodium transfers an electron to Chlorine.

  11. Ionic Bonds • Another look at it:

  12. Predicting Ionic Bonds • Generally speaking, you can tell what kind of charge an atom likes to form by how many valence electrons it has.

  13. Positive and Negative • Think of Calcium. How many valence electrons does it have? • 2. • Is it easier for it to gain six valence electrons to be like Krypton or to lose two to be like Argon? • Lose 2. • And if it loses 2 negatively-charged electrons, what ionic charge does it now have? • 2+ http://chemicalelements.com/elements/ca.html

  14. Positive and Negative • Think of Nitrogen. How many valence electrons does it have? • 5. • Is it easier for it to gain three valence electrons to be like Neon or to lose five to be like Helium? • Gain 3. • And if it gains 3 negatively-charged electrons, what ionic charge does it now have? • 3- http://chemicalelements.com/elements/n.html

  15. Lose Electrons Gain Electrons

  16. Do Not Ionize Form 3- ions. Form 2- ions. Form 1- ions. Form 1+ ions. Form 2+ ions. Form 3+ ions.

  17. Ionic Bonds • Summarizing Ionic Bonds: • Typically positive atom + negative atom. • Usually opposite ends of the Periodic Table. • Electrons are transferred. • Bond is formed because of the attraction between positive and negative. • Like the opposite poles of magnets.

  18. Ionic Bonding Animation • Ionic Bonding Animation – Teacher’s Domain

  19. Covalent Bonds • What does the word covalent sound like? • Think of it as co-valence. • In a covalent bond, electrons are shared. • Both nuclei are pulling on the electrons being shared, but neither can quite take it away. • This “tug of war” between the atoms is what bonds them together. • Animation on next slide.

  20. BondsCovalent How to remember: covalent = cooperative

  21. Covalent Bonds • What it looks like: Notice that even though only one electron is needed by each, the atoms share two. http://www.ider.herts.ac.uk/school/courseware/materials/images/covalent_bonding.gif

  22. Covalent Bonds • In this example, oxygen has 6 valence electrons. It needs two electrons. • Each hydrogen has one valence electron. They both need one electron each.

  23. Covalent Bonds • Covalent Bonding Animation – Teacher’s Domain

  24. Another Covalent Bond Example • Methane – CH4 – 1 Carbon, 4 Hydrogen • Methane is a key ingredient in…? • Farts! (seriously)

  25. Carbon • Why is carbon special? • 4 valence electrons • Valence shell can hold 8 electrons • Carbon can bond to lots of other atoms/molecules on each side. • See drawing… • What you need to know: • Carbon is special because it can make long chains or rings by bonding to other carbons and many other atoms. • This is part of the reason carbon supports life. We’ll learn more about these carbon-based molecules in a few lessons.

  26. Carbon’s Special • CrashCourse – That’s Why Carbon is a Tramp

  27. Covalent Bonds • Summarizing Covalent Bonds: • Typically between two atoms that both have near-capacity valence electrons. • Electrons are shared (or fought-over), and that sharing (or fighting) is what keeps the atoms together.

  28. One last one… • There’s also the hydrogen bond. It’s very simple. Here it is…

  29. BondsHydrogen How to remember: Hydrogen bonds are strong bonds between molecules involving hydrogen (and usually O, N, F). Just remember that.

  30. It’s not quite a bond, but… • There’s also this force called the van der Waals force. • This is a force that holds molecules together due to weak forces between oppositely charged regions of different molecules. • In other words, the protons of one atom *slightly* hold onto the electrons of another atom. • Generally a weak force, and not a conventional bond.

  31. Van der Waals Force

  32. Van der Waals Forces • Where do we see van der Waals forces in nature? • Geckos, for one! http://duende.uoregon.edu/~hsu/blogfiles/gecko.jpg http://cdn.physorg.com/newman/gfx/news/2005/gecko.jpg

  33. Geckos

  34. Quia Activities • One computer per pair. • Start with Battleship (1 player – work together): • Atomic Structure and Electron Configuration Battleship • Move on to Battleship (1 player – work together): • Bond Battleship • Move on to the Challenge Board (2 player): • Atomic Structure, Bonds, and Electron Configuration Challenge Board

  35. Closure • Dogs Teaching Chemistry

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