Chapter 9 Chemical Bonding Theories Valence Bond Theory Uses Lewis Structures Bonds form using shared electrons between overlapping orbitals on adjacent atoms Orbitals arrange around central atom to avoid each other Two types of bonds sigma and pi Molecular Orbital Theory Uses MO Diagrams Orbitals on atoms mix to make molecular orbtials which go over 2 or more atoms Two electrons can be in an orbital Orbitals are either bonding antibonding or nonbonding Bonds are either sigma or pi Sigma Bonding Orbitals on bonding atoms overlap directly between bonding atoms Between s orbitals Between p orbitals Sigma s Bonding Consider VSEPR Shapes and bonding What s wrong with this picture Atoms bond by having their valence orbitals overlap 2pz 2s 2px Orbitals on C 2py Orbitals in CH4 Orbitals don t go in same directions as atomic orbitals 2pz 2s 2px 2py Orbitals in CH4 Orbitals don t go in same directions as atomic orbitals Conclusion Atomic orbitals change shape when they make molecules Hybrid Orbitals Atomic valence orbitals combine and mix to form new Hybrid Orbitals Hybrid orbitals go in the VSEPR electron geometry directions Types of Hybrid Orbitals Types of Hybrid Orbitals 2 Pairs Types of Hybrid Orbitals 3 Pairs Types of Hybrid Orbitals 4 Pairs Hybrid orbitals used for sigma bonds and lone pairs Unhybridized p orbitals used for pi bonds or they are empty Sigma Bonding Orbitals overlap directly between two nuclei NH3 CH2O Sigma vs Pi Bonding Sigma Bonding involves hybrid orbitals and or H 1s orbitals Pi bonding involves unhybridized p orbitals Pi Bond Formation Bonding in Ethene Bonding in Acetylene Bonding in Formaldehyde Bonding in Benzene Advanced Allene Each end carbon is a flat trigonal Are they co planar or perpendicular Bonding in Allene Conformations vs Isomers Isomers Molecules with same formula but different structure Conformers Different temporary shapes of the same molecule Bond Rotations CAN happen around single bonds Cannot happen around double bonds Cis Trans Isomerization When two groups are on a side of a molecule cis trans Can these molecules have cis trans isomers
View Full Document
Unlocking...