Today is Thursday, September 19th, 2013 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)?

Today’s Agenda Bonding Forces sort of like 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

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

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.

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.

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.

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…

Bonds Ionic How to remember: Ions are selfish

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

Ionic Bonds So Sodium transfers an electron to Chlorine.

Ionic Bonds Another look at it:

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

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

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

Lose Electrons Gain Electrons

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

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.

Ionic Bonding Animation Ionic Bonding Animation – Teacher’s Domain

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.

Bonds Covalent How to remember: covalent = cooperative

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

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.

Covalent Bonds Covalent Bonding Animation – Teacher’s Domain

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

Carbon Why is carbon special? What you need to know: 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.

Carbon’s Special CrashCourse – That’s Why Carbon is a Tramp

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.

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

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

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.

Van der Waals Force

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

Geckos

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

Closure Dogs Teaching Chemistry