Chp 2 Molecular Orbital Theory, Orbital Hybrid, & IMFA

• Molecular Orbital Theory, Intermolecular Forces, and Acid-Base Organic Reactions are topics discussed in BIOL 103 Session 2.
• Atomic Orbitals (AOs) are the physical reality of Y squared, which gives the probability of finding an electron in a particular location in space.
• Group can overwhelm the ability of the polar group to solubilize a molecule in water.
• One hydrophilic group such as hydroxyl can make a compound with 3 carbons completely soluble in water.
• Plots of Y squared in three dimensions generate the shape of s, p, d, and f orbitals.
• Only s and p orbitals are very important in organic chemistry.
• An orbital is a region in space where the probability of finding an electron is large.
• The typical representation of orbitals are those volumes which contain the electron 90-95% of the time.
• 1 s and 2 s orbitals are spheres centered around the nucleus.
• Each orbital can accommodate 2 electrons.
• The 2 s orbital is higher in energy and contains a nodal surface (Y = 0) in its center.
• Each 2 p orbital has two nearly touching spheres (or lobes).
• There are three 2 p orbitals which are perpendicular (orthogonal) to each other.
• The 2 p orbitals are higher in energy than the 1 s or 2 s.
• Aufbau Principle: The lowest energy orbitals are filled first.
• The axis that passes through the center of the sp orbitals is referred to as the sp axis.
• Ethyne depictions show that the electron density around the carbon-carbon bond has circular symmetry.
• Even if rotation around the carbon-carbon bond occurred in ethyne, a different compound would not result.
• The carbon-carbon bond length is shorter as more bonds hold the carbons together.
• With more electron density between the carbons, there is more "glue" to hold the nuclei of the carbons together.
• The carbon-hydrogen bond lengths also get shorter with more s character of the bond.
• 2s orbitals are held more closely to the nucleus than 2p orbitals.
• A hybridized orbital with more percent s character is held more closely to the nucleus than an orbital with less s character.
• The sp orbital of ethyne has 50% s character and its C-H bond is shorter.
• The sp3 orbital of ethane has only 25% s character and its C-H bond is longer.
• The strength of intermolecular forces determines the physical properties.
• Pauli Exclusion Principle: A maximum of two spin paired electrons may be placed in each orbital.
• Hund’s Rule: One electron is added to each degenerate (equal energy orbital) before a second electron is added.
• Cr: 3d^6
• Cr: 3d^5
• Cr: 3d^4
• Cr: 3d^3
• Cr: 3d^2
• Cr: 3d
• Cr: 2d^6
• Cr: 2d^5
• Cr: 2d^4
• Cr: 2d^3
• Cr: 2d
• Melting point, boiling point and solubility are influenced by stronger intermolecular forces.