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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

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 by orbital overlap

Sigma Bond Formation by Orbital Overlap

Two s orbitals overlap


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 CH4


The end game

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 glycine1

Bonding in Glycine


Bonding in glycine2

Bonding in Glycine


Bonding in glycine3

Bonding in Glycine


Bonding in glycine4

Bonding in Glycine


Bond types

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

Multiple Bonds

Consider ethylene, C2H4


Sigma bonds in c 2 h 4

Sigma Bonds in C2H4


Bonding in c 2 h 4

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.


Bonding in c 2 h 41

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 bonding in c 2 h 4

Multiple Bondingin C2H4


S and bonding in c 2 h 4

sand π Bonding inC2H4


S and bonding in ch 2 o

sand π Bonding inCH2O


S and bonding in c 2 h 2

sand π Bonding inC2H2


Consequences of multiple bonding

Consequences of Multiple Bonding

There is restricted rotation around C=C bond.


Consequences of multiple bonding1

Consequences of Multiple Bonding

Restricted rotation around C=C bond.


Double bonds and vision

Double Bonds and Vision


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