Ch 101 1st Edition Lecture 13 Outline of Last Lecture I Equivalent Resonance Structures II Preferred Resonance Structures III Molecular Structure IV Bond Order A Finding the Oxidation State using the Electron Counting Method Outline of Current Lecture I Bond Order in Complex Molecules II Pi and Sigma Bonds III Introduction to Hybridization Current Lecture I Bond Order in Complex Molecules On the test you will most likely be given a picture of a very strange and complicated looking molecule and asked to state the bond order of a certain bond in the molecule This first thing you would need to do is determine the possible resonance of the bond This will help you determine how many bonds and bonding region there are to help you find the length strength of the bond In this molecule the bond order for the C C bonds is 3 2 because there are 9 bonds and 6 bonding regions 9 6 simplifies to 3 2 You do not include the C H bonds because if you draw out the different resonance structures the C H bonds do not change but the C C bonds change which bonds get a double bond You can visualize the bond order like the picture below where all of the C C bonds have bonds of the same length between them These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II Pi and Sigma Bonds Sigma bonds Electron density between atoms this is the first bond atoms make between each other Sigma bonds are stronger than Pi bonds and are made from hybridized orbitals OR Pi bonds Electron density above and below atoms every second or third bond is a Pi bond Pi bonds are weaker because their bonds are made between more electrons that are farther from the nucleus III Identifying Sigma and Pi bonds is simple If it is a single bond it is a sigma bond If it is a double bond one bond is a sigma bond and the other is a Pi bond If it is a triple bond one is a sigma bond and the other two are Pi bonds Here is a made up molecule with the sigma and pi bonds labeled with the symbol for sigma and for pi Hybridization Hybridization is simply the mixing of orbitals to form hybridized orbitals The first two electrons that bond a sigma bond come together and then the rest of the electrons in all of the other orbitals mix together to form a molecule that is symmetrical Hybridization is a way to explain how a molecule has equal angles between all of its atoms An easy way to name Hybridization states is to just look at the bonds and see that A central atom with no multiple bonds only single bonds has a hybridization of sp3 A central atom with one double bond has a hybridization of sp2 A central atom with two double bonds or one single bond has a hybridization of sp There is also another way to find the Hybridization state if you are good at naming bond angles Each hybridization state corresponds to a bond angle therefore if you know the bond angle you know the hybridization state and vice versa Here is a chart of the corresponding Hybridization states and bond angles Shape Bond Angle Hybridization State Linear 180o sp Bent Trigonal Planar 120o sp2 Trigonal Pyramidal Bent Angular Tetrahedral 109o sp3 Ex What is the hybridization of the labeled atom There are many ways to approach this question let s try both of the ways I have described above One double bond sp2 One double bond means that the hybridization is sp2 Trigonal Planer 120o sp2 We can check our answer by seeing if the bond angle correlates to the hybridization