*The molecular geometry, or the shape of a molecule is described by the geometric figure formed when the atomic nuclei are imagined to be joined in straight lines.EOS

*Ideal molecular geometry is based on the idea that pairs of valence electrons in bonded atoms repel one anotherAn electron group is any collection of valence electrons, localized in a region around a central atom, that repels other groups of valence electrons

*How can electrons on the central atom be arranged so they are as far apart as possible?

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*The optimal repulsion arrangement is opposite ends of a line

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*The optimal repulsion arrangement is at the face centers of a cube

*EOSIllustration

*This overlap region has a high electron charge density

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*Most of the electrons in a molecule remain in the same orbital locations that they occupied in the separated atomsBonding electrons are localized in the region of atomic orbital overlap

*HybridizationVideo

*Occurs most often for central atom only

*EOSThe carbon atom in methane (CH4) has bonds that are sp3 hybrids

Note that in this molecule carbon has all single bonds

*EOSAmmonia (NH3) is similar except the lone pair of electrons occupies the 4th hybrid orbital

*This hybridization scheme is useful in describing double covalent bondsComprised of one 2s orbital and two 2p orbitals to produce a set of three sp2 hybrid orbitals

*The geometric distribution of the three sp2 hybrid orbitals is within a plane, directed at 120o angles

*This hybridization scheme is useful in describing triple covalent bonds

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*In hybridization schemes, one hybrid orbital is produced for every simple atomic orbital involvedWrite a plausible Lewis structure for the molecule or ionUse the VSEPR method to predict the electron-group geometry of the central atomSelect the hybridization scheme that corresponds to the VSEPR prediction

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*Covalent bonds formed by the end-to-end overlap of orbitals, regardless of orbital type, are called sigma (s) bonds. All single bonds are sigma bondsA bond formed by parallel, or side-by-side, orbital overlap is called a pi (p) bondA double bond is made up of one sigma bond and one pi bond

*EOSA double bond is made up of one sigma bond and one pi bond

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*Geometric isomers are isomers that differ only in the geometric arrangement of certain substituent groups

*Molecular orbitals (MOs) are mathematical equations that describe the regions in a molecule where there is a high probability of finding electronsMolecular orbitals (MOs) are essentially combinations of atomic orbitals two types exist, bonding and antibonding orbitals

*The hydrogen moleculeAntibonding MO = region of diminished electron density

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*Bonding MOs s AOs = s MOsp AOs = p MOs

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Those diatomic molecules containing atoms of different elements. Examples are HCl, CO, CN- and NO. To draw the molecular orbital diagrams for heteronuclear diatomic molecules, we face a new problem: where do we place the atomic orbitals on an atom relative to atomic orbitals on other atoms? For example, how can we predict whether a carbon 2s or an oxygen 2s orbital is lower in energy? The answer comes from our understanding of electronegativity. Oxygen is more electronegative than carbon. The more electronegative element's orbitals are placed lower on the molecular orbital diagram than those of the more electropositive element.*

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Consider the HCl molecule. Combination between the hydrogen 1s AO and the chlorine 1s, 2s, 2p and 3s orbitals can be ruled out because their energies are too low. If overlap occurred between the chlorine 3py and 3pz orbitals it would be non-bonding because the positive lobe of hydrogen will overlap equally with the positive and negative lobes of the chlorine orbitals. The combination of H, 1s1, and Cl, 3px1, gives both bonding and antibonding orbitals, and the two electrons occupy the bonding MO, leaving the antibonding MO empty. It is assumed that all the chlorine AOs except 3px are localized on the chlorine atom and retain their original AO status, and the 3s, 3py and 3pz orbitals are regarded as non-bonding lone pairs.*

The VSEPR method is used to predict the shapes of molecules and polyatomic ionsIf all electron groups are bonding groups, the molecular geometry is the same as the electron-group geometryA polar covalent bond has separate centers of positive and negative charge, creating a bond dipole*EOS

In the valence bond theory, a covalent bond is formed by the overlap of atomic orbitals of the bonded atoms in a region between the atomic nucleiHybridized orbitals include sp, sp2, sp3, sp3d, and sp3d2*

Single bonds are all hybridized s bonds, double bonds have one s bond and one p bond, and triple bonds have one s bond and two p bondsIn molecular orbital theory, atomic orbitals of separated atoms are combined into molecular orbitalsThe benzene molecule is usually represented by its resonance hybrid*

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