Chpt 9 mo theory
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Chpt 9 - MO Theory. Localized e - model and hybrid orbitals sigma (  ) and pi (  ) bonds HW: Chpt 9 - pg. 430-437, #s 11, 12, 16, 29all, 32, 37, Due Mon Nov. 29. Covalent Bonding. Recall

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Chpt 9 - MO Theory

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Chpt 9 mo theory

Chpt 9 - MO Theory

  • Localized e- model and hybrid orbitals

  • sigma () and pi () bonds

  • HW: Chpt 9 - pg. 430-437, #s 11, 12, 16, 29all, 32, 37, Due Mon Nov. 29


Covalent bonding

Covalent Bonding

Recall

  • A bond is a combination of forces that hold groups of atoms together and make them function as a unit.

  • A bond will form if the energy of the aggregate is lower than that of the separated atoms.


Rationale for orbital hybridization

Rationale for Orbital Hybridization

What is shape and bond angles of CH4?

What is the valence electron configuration of a carbon atom?

s2p2

We now want to think of the bonding orbitals for methane as being formed by an overlap of atomic orbitals.

Assume that the carbon atom has four equivalent atomic orbitals, arranged tetrahedrally.


Hybridization

Hybridization

Mixing of the native atomic orbitals to form special orbitals for bonding.

sp3 Hybridization

  • Combination of one s and three p orbitals.

  • Whenever a set of equivalent tetrahedral atomic orbitals is required by an atom, the localized electron model assumes that the atom adopts a set of sp3 orbitals; the atom becomes sp3 hybridized.


Energy diagram for sp 3

Energy diagram for sp3

An s and 3 p orbitals become 4 equal sp3 orbitals

visualization


C 2 h 4 example

C2H4 example

Draw the Lewis structure for C2H4 (ethylene)?

  • What is the shape of an ethylene molecule?

    trigonal planar around each carbon atom

  • What are the approximate bondangles around the carbon atoms?

    120o


Sp 2 hybridization energy level diagram

sp2 hybridization & Energy level diagram

  • Combination of one s and two p orbitals.

  • Gives a trigonal planar arrangement of atomic orbitals.

  • One p orbital is not used.

    • Oriented perpendicular to the plane of the sp2 orbitals can be used to form pi () bonds.


Ethylene c 2 h 4 hybrid bonding

Ethylene C2H4 hybrid bonding

Carbon atom

Carbon atom


Ethylene sigma and pi bonding

Ethylene sigma and pi bonding

Above - sigma bonds in ethylene

Above - sigma bond & pi bond on carbon in ethylene

Left - total bonding in ethlene


Sp hybridization example

sp hybridization example

Draw the Lewis structure for CO2. 

  • What is the shape of a carbon dioxide molecule?

    linear

  • What are the bond angles?

    180o


Sp hybridization

sp Hybridization

  • Combination of one s and one p orbital.

  • Gives a linear arrangement of atomic orbitals.

  • Two p orbitals are not used.

    • Needed to form the  bonds.


Sigma pi bonds

Sigma & Pi bonds

Sigma () bond

  • an Electron pair is shared in an area centered on a line running between the atoms.

    Pi () bond

  • Forms double and triple bonds by sharing electron pair(s) in the space above and below the σ bond.

  • Uses the unhybridized p orbitals.


Hybrid orbitals in co 2

Hybrid orbitals in CO2

Yellow are 2 sp hybrid orbitals --> make  bonds to O , Blue are unhybridized p orbitals that make  bonds to O (double bonds)


Dsp 3 hybridization

dsp3 hybridization

Draw the Lewis structure for PCl5.

  • What is the shape of a phosphorus pentachloride molecule?

    trigonal bipyramidal

  • What are the bond angles?

    90o and 120o

  • Combination of one d, one s, and three p orbitals.

  • Gives a trigonal bipyramidal arrangement of five equivalent hybrid orbitals.


D 2 sp 3 hybridization

d2sp3 Hybridization

Draw the Lewis structure for XeF4.

  • What is the shape of a xenon tetrafluoride molecule?

    octahedral

  • What are the bond angles?

    90o and 180o

  • Combination of two d, one s, and three p orbitals.

  • Gives an octahedral arrangement of six equivalent hybrid orbitals.


Xef 4 example

XeF4 example


Examples

Examples

Draw the Lewis structure for HCN.

Which hybrid orbitals are used?

Draw HCN:

  • Showing all bonds between atoms.

  • Labeling each bond as  or .


More examples hybridization

More examples hybridization

Determine the bond angle and expected hybridization of the central atom for each of the following molecules:

NH3SO2KrF2

CO2ICl5

NH3 – 109.5o, sp3

SO2 – 120o, sp2

KrF2 – 90o, 120o, dsp3

CO2 – 180o, sp

ICl5 – 90o, 180o, d2sp3


No 3 1 delocalized pi orbital

NO3-1 delocalized pi orbital


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