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Advanced Theories of Chemical Bonding. Atomic Orbitals. Molecules. Warm-up. What are Lewis Dot Structures for SO 2 , SOCl 2 , SO 2 Cl 2 , FSO 3 1- Draw the Lewis Dot structure for CH 4 (methane) How many bonds does Carbon make? Write the orbital notation for Carbon (the one with arrows)

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Presentation Transcript

Advanced Theories of

Chemical Bonding

Atomic Orbitals

Molecules


Warm up
Warm-up

  • What are Lewis Dot Structures for

    • SO2, SOCl2, SO2Cl2, FSO31-

  • Draw the Lewis Dot structure for CH4 (methane)

    • How many bonds does Carbon make?

    • Write the orbital notation for Carbon (the one with arrows)

    • There is a conflict in these two models, what is it?


Objectives
Objectives

  • Understand Hybrid Orbitals

    • Explain what a hybrid orbital is

    • Identify hybrid orbitals present within a molecule

    • Know what a sigma bond is

    • Know what a pi bond is

    • Know the consequences of the presence of a pi bond within a molecule


Two theories of bonding
Two Theories of Bonding

  • MOLECULAR ORBITAL THEORY — Robert Mullikan (1896-1986)

  • valence electrons are delocalized

  • valence electrons are in orbitals (called molecular orbitals) spread over entire molecule.


Two theories of bonding1
Two Theories of Bonding

  • VALENCE BOND THEORY — Linus Pauling (1901 -1994)

  • valence electrons are localized between atoms (or are lone pairs).

  • half-filled atomic orbitals overlap to form bonds.



Sigma bond formation
Sigma Bond Formation

Two s orbitals overlap

Two p orbitals overlap


Using vb theory
Using VB Theory

Bonding in BF3

planar triangle

angle = 120o


Bonding in bf 3
Bonding in BF3

  • How to account for 3 bonds 120o apart using a spherical s orbital and p orbitals that are 90o apart?

  • Pauling said to modify VB approach with ORBITAL HYBRIDIZATION

  • — mix available orbitals to form a new set of orbitals — HYBRID ORBITALS — that will give the maximum overlap in the correct geometry.


Bonding in bf 31

2p

2s

hydridize orbs.

rearrange electrons

2

unused p

three sp

orbital

hybrid orbitals

Notice that from an s and a p subshell, there are four possible equal sp orbitals that COULD be formed

Bonding in BF3


Bonding in bf 32
Bonding in BF3

  • The three hybrid orbitals are made from 1 s orbital and 2 p orbitals  3 sp2 hybrids.

  • Now we have 3, half-filled HYBRID orbitals that can be used to form B-F sigma bonds.


Bonding in bf 33
Bonding in BF3

An orbital from each F overlaps one of the sp2 hybrids to form a B-F  bond.


Bonding in ch 4
Bonding in CH4

How do we account for 4 C—H sigma bonds 109o apart?

Need to use 4 atomic orbitals — s, px, py, and pz — to form 4 new hybrid orbitals pointing in the correct direction.


Bonding in a tetrahedron formation of hybrid atomic orbitals
Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals

4 C atom orbitals hybridize to form four equivalent sp3 hybrid atomic orbitals.


Bonding in a tetrahedron formation of hybrid atomic orbitals1
Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals

4 C atom orbitals hybridize to form four equivalent sp3 hybrid atomic orbitals.


Bonding in ch 41
Bonding in CH Orbitals4


The end game
The end game Orbitals

e- pair geom. Hybrid. Unhybrid. Orbitals

Linear sp 2 p’s

Trigonal planar sp2 1 p

Tetrahedral sp3 0 p

Trigonal-bipyramidal sp3d –

Octahedral sp3d2 –







Bond types
Bond Types Orbitals

  • Sigma (σ) – arise from the overlap of atomic orbitals (including hybridized orbitals) where e- lie along the axis between the nuclei of atoms in bond

  • Pi (π ) – arise when overlap occurs above or below the nuclei axis (these are p-orbitals that are not hybridized)

  • FYI D.B. is result of a sigma and a pi

  • Make C2H2 and CO2, What explains this shape?


Multiple bonds
Multiple Bonds Orbitals

Consider ethylene, C2H4


Sigma bonds in c 2 h 4
Sigma Bonds in C Orbitals2H4


Bonding in c 2 h 4
π Bonding in C Orbitals2H4

The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital on the neighboring atom to form the π bond.


Bonding in c 2 h 41
π Bonding in C Orbitals2H4

The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital on the neighboring atom to form the π bond.


Multiple bonding in c 2 h 4
Multiple Bonding Orbitalsin C2H4


S and bonding in c 2 h 4
s Orbitalsand π Bonding inC2H4


S and bonding in ch 2 o
s Orbitalsand π Bonding inCH2O


S and bonding in c 2 h 2
s Orbitalsand π Bonding inC2H2


Consequences of multiple bonding
Consequences of Multiple Bonding Orbitals

There is restricted rotation around C=C bond.


Consequences of multiple bonding1
Consequences of Multiple Bonding Orbitals

Restricted rotation around C=C bond.



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