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**Hybridization, Polarity, & Electronegativity**

Lots of multisyllabic words, I know

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Overlap and Bonding We think of covalent bonds forming through the sharing of electrons by adjacent atoms. In such an approach this can only occur when orbitals on the two atoms overlap.

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Hybridization Atomic orbitals (s, p, d, f) cannot adequately explain the bonding in molecules Consider CH4 … how do we get the tetrahedral shape out of the above orbitals

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**Hybridization Consider beryllium:**

An averaging of atomic orbitals into a new set of “hybrid orbitals” Consider beryllium: In its ground electronic state, it would not be able to form bonds because it has no singly-occupied orbitals.

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**Hybridization Consider beryllium:**

if it absorbs the small amount of energy needed to promote an electron from the 2s to the 2p orbital, it can form two bonds.

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Hybrid Orbitals Mixing the s and p orbitals yields two degenerate orbitals that are hybrids of the two orbitals. These sp hybrid orbitals have two lobes like a p orbital. One of the lobes is larger and more rounded as is the s orbital.

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Hybrid Orbitals These two degenerate orbitals would align themselves 180 from each other. This is consistent with the observed geometry of beryllium compounds: linear.

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Hybrid Orbitals With hybrid orbitals the orbital diagram for beryllium would look like this. The sp orbitals are higher in energy than the 1s orbital but lower than the 2p.

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**Hybrid Orbitals Think about Boron What’s its electron configuration?**

How many bonds does it normally form? How?

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Hybrid Orbitals …three degenerate sp2 orbitals.

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Hybrid Orbitals For Carbon:

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Hybrid Orbitals …four degenerate sp3 orbitals.

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Hybrid Orbitals For geometries involving expanded octets on the central atom, we must use d orbitals in our hybrids.

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**Hybrid Orbitals This leads to five degenerate sp3d orbitals…**

…or six degenerate sp3d2 orbitals.

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Hybrid Orbitals Once you know the electron-domain geometry, you know the hybridization state of the atom. Short cut… count the bonded electron domains… that’s the number of hybridizations.

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# Hybrid Orbitals Hybridization Bond Angles Electron Pair Geometry 2 sp 180 Linear 3 sp2 120 Trigonal planar 4 sp3 109 Tetrahedral 5 sp3d 120,90 Trigonal bipyramidal 6 sp3d2 90 octahedral

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Practice Problems Specify the electron-pair and molecular geometry for each underlined atom in the following list. Describe the hybrid orbital set used by this atom in each molecule or ion. BBr3 CO2 CH2Cl2 CO3-2

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**Practice Problems Answers**

Electron-Pair Molecular Hybrid Geometry Geometry Orbital Set Trigonal Planar Trigonal Planar sp2 Linear Linear sp Tetrahedral tetrahedral sp3 Trigonal planar trigonal planar sp2

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**Types of Covalent Bonds**

According to the valence bond theory, bond formation requires that two orbitals on adjacent atoms to overlap…. So what about multiple bonds… Draw C2H4 Is there room in between the two atoms for two pairs of electrons to share space? NO

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**Types of Covalent Bonds**

Sigma (σ) Formed from the overlap of hybrid orbitals. Electron density along the internuclear axis… between the centers of the atoms…

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**Types of Covalent Bonds**

Pi (π) Formed from the overlap of unhybridized p-orbitals. Electron density is above and below the internuclear axis, between the atomic centers

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**Types of Covalent Bonds**

Draw Aceylene:C2H2 In triple bonds, two sp orbitals form a bond between the carbons, and two pairs of p orbitals overlap in fashion to form the two bonds. Or there is always one sigma bond… anything more is a pi bond

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**Molecular Orbital Theory**

ATOMS Electrons in Orbitals s, p, d, f, etc MOLECULES Experimental Geometries Linear, trigonal planar, tetrahedral Molecular Orbital Theory: Atomic orbitals from all atoms combine to form new orbitals resulting in known geometries Hybridization: Atomic orbitals from single atoms combine to form new orbitals resulting in known geometries VESPER: Electrons repel; moleular shapes result.

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**Molecular Orbital Theory**

Molecular orbitals are formed by combinations of atomic orbitals from different atoms. There are bonding and antibonding orbitals Without significant electrons density between them, the nuclei will repel each other… creating antibonding orbitals

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**Molecular Orbital Theory**

First Principle of MO Theory the total number of molecular orbitals is always equal to the total number of atomic orbitals contributed by the atoms that have combined. Second Principle of MO Theory The bonding molecular orbital is lower in energy than the parent orbitals, and the antibonding orbital is higher in energy

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**Molecular Orbital Theory**

Third Principle of MO Theory Electrons of the molecule are assigned to orbitals of successively higher energy Fourth Principle of MO Theory Atomic orbitals combine to form molecular orbitals most effectively when the atomic orbitals are of similar energy

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**Molecular Orbital Theory**

# of molecular orbitals = # of atomic orbitals Equal # of bonding and antibonding orbitals Antibonding orbitals ALWAYS higher in energy than its BONDING COUNTERPART Basically, it means that these guys will fill in from the bottom up… from lower energy to higher energy…

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**Molecular Orbital Theory**

Can use this to calcualte bond order Bond Order = ½ [(# e- in bonding orbitals) – (# of e- in antibonding orbitals)] What is the bond order of Ne2+? Bond order = (8-7)/2 = ½

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