Presentation on theme: "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 Tues."— Presentation transcript:
Chpt 9 - MO Theory Localized e - model and hybrid orbitals sigma ( ) and pi ( ) bonds HW: Chpt 9 - pg , #s 11, 12, 16, 29all, 32, 37, Due Tues Nov. 17 Chpt 6 Review Homework: #30, 36, 46, 50, 60, 74, 78
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 What is shape and bond angles of CH 4 ? What is the valence electron configuration of a carbon atom? s2p2 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 Mixing of the native atomic orbitals to form special orbitals for bonding. sp 3 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 sp 3 orbitals; the atom becomes sp 3 hybridized.
Energy diagram for sp 3 An s and 3 p orbitals become 4 equal sp 3 orbitals visualization
C 2 H 4 example Draw the Lewis structure for C 2 H 4 (ethylene)? What is the shape of an ethylene molecule? trigonal planar around each carbon atom What are the approximate bond angles around the carbon atoms? 120 o
sp 2 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 sp 2 orbitals can be used to form pi ( ) bonds.
Ethylene C 2 H 4 hybrid bonding Carbon atom
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 Draw the Lewis structure for CO 2. What is the shape of a carbon dioxide molecule? linear What are the bond angles? 180 o
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 ( ) 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 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 Draw the Lewis structure for PCl 5. What is the shape of a phosphorus pentachloride molecule? trigonal bipyramidal What are the bond angles? 90 o and 120 o 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 Draw the Lewis structure for XeF 4. What is the shape of a xenon tetrafluoride molecule? octahedral What are the bond angles? 90 o and 180 o Combination of two d, one s, and three p orbitals. Gives an octahedral arrangement of six equivalent hybrid orbitals.
XeF 4 example
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 Determine the bond angle and expected hybridization of the central atom for each of the following molecules: NH 3 SO 2 KrF 2 CO 2 ICl 5 NH 3 – o, sp 3 SO 2 – 120 o, sp 2 KrF 2 – 90 o, 120 o, dsp 3 CO 2 – 180 o, sp ICl 5 – 90 o, 180 o, d 2 sp 3