CHEM 2211 1st Edition Lecture 1 Outline of Current LectureI. Molecular Orbital Theory (MO)II. Linear Conservation of Atomic Orbitals (LCAO)VocabularyAtomic OrbitalMolecular OrbitalConstructive OverlapDestructive OverlapNodes (nodal)AntibondingSigma bondsElectron ConfigurationSigma StarElectronegativity (electronegative)Electron DensityCurrent LectureI. Molecular Orbital Theory (MO)A. Atomic orbitals are the halo around an atom’s nucleus where electrons are most likely going to beB. Molecular Orbitals are the combination of atomic orbitalsC. MO’s add both constructively and destructivelyi. Constructive overlap occurs when two atoms in the same phase add together to create a large molecular orbit.ii. Destructive overlap occurs when two atoms out of phase try to bond. When they contact, each atom’s electron try to move as far away as possible, creating a Nodal space in between where no electrons are present. This effect is called Antibonding.Figure 1 As Hydrogen atoms begin to bond, their atomic orbitals begin to fuse into onemolecular orbital. This is an example of Constrictive overlap.Figure 2 When out of phase Hydrogen atoms try to bond they create a nodal space where noelectrons exist. This is called Destructive Overlap and is characteristic of Antibonding.II. Linear Conservation of Atomic OrbitalsA. In order to a count for all the electrons, the number of atomic orbitals consumed is equal to the number of molecular orbitals formed2 Atomic Orbitals + 2 Atomic Orbitals = 4 Molecular OrbitalsB. Recall that Hydrogen atoms form sigma bonds when bonded AND have a 1s1 electron configurationC. As seen figure three, the 2 individual Hydrogen atoms (on the left and right) combine their electrons to create a sigma bond (at the bottom). i. The sigma star orbital at the represent the Antibonding orbital and is filled when the bond between the Hydrogens is broken.Figure 3D. Let’s see the same phenomenon in the pi bonds of ethyleneFigure 4 EthyleneE. The only change between the carbons bonding and the hydrogens bonding is the presence of the double pi bondF. What happens when one molecule in a bond is more electronegative than the other as seen in the carbon/oxygen bond of the carbonyl functional group?Figure 5 Carbonyl Functional GroupG. Because Oxygen is more electronegative than Carbon, it has a higher electron density. This density causes the oxygen to be more similar to the sigma bond than the carbon. Conversely, because the carbon has fewer electrons around it, itis closer in similarity to the empty pi star orbital.Figure
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