Advanced Theories of
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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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Advanced Theories of Chemical Bonding

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Advanced Theories of

Chemical Bonding

Atomic Orbitals

Molecules


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

  • 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

  • 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 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 by Orbital Overlap

Two s orbitals overlap


Sigma Bond Formation

Two s orbitals overlap

Two p orbitals overlap


Using VB Theory

Bonding in BF3

planar triangle

angle = 120o


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.


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 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 BF3

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


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

4 C atom orbitals hybridize to form four equivalent sp3 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 CH4


The end game

e- pair geom.Hybrid. Unhybrid. Orbitals

Linearsp2 p’s

Trigonal planarsp21 p

Tetrahedralsp30 p

Trigonal-bipyramidalsp3d –

Octahedralsp3d2 –


Bonding in Glycine


Bonding in Glycine


Bonding in Glycine


Bonding in Glycine


Bonding in Glycine


Bond Types

  • 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

Consider ethylene, C2H4


Sigma Bonds in C2H4


π Bonding in C2H4

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.


π Bonding in C2H4

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 Bondingin C2H4


sand π Bonding inC2H4


sand π Bonding inCH2O


sand π Bonding inC2H2


Consequences of Multiple Bonding

There is restricted rotation around C=C bond.


Consequences of Multiple Bonding

Restricted rotation around C=C bond.


Double Bonds and Vision


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