Methane, CH 4 less repulsion between the bonding pairs of electrons 109.5° 90°

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Presentation transcript:

methane, CH 4 less repulsion between the bonding pairs of electrons 109.5° 90°

.. ammonia NH 3

° (109.5°) 109.5° (107°) 109.5° (104.5°) water, H 2 O

Ozone O 3

Formaldhyde H 2 CO

Hydrogen Cyanide HCN

Are there atomic orbitals on C, Si, N and O to accommodate the bonding electrons of the shapes predicted by VSEPR? s orbital 3 p orbitals x y z x y z

x y z x y z Are there atomic orbitals on C, Si, N and O to accommodate the bonding electrons of the shapes predicted by VSEPR?

4 sp 3 orbitals x y z Are there atomic orbitals on C, Si, N and O to accommodate the bonding electrons of the shapes predicted by VSEPR?

4 sp 3 orbitals x y z C H H H H

s + p x + p y = 3 sp 2 orbitals p z orbital

O C H H

C O H H

s + p x = 2 sp orbitals P y orbital P z orbital

C N

CN

CN

CN

CN H

VSEPR shape bonding hybrid orbitals tetrahedral trigonal planar linear sp 3 sp 2 sp

Review: Ethane sp 3 C sp3 -H s C sp3 -C sp3

Review: Ethane sp 3 H C H H H H H C ● ● C sp3 -H s C sp3 -C sp3

Hybrid atomic orbitals Why are hybrid orbitals used in chemical bonding? s orbital and s - p x + - p orbital x p x s +....

molecular orbitals. a C-C bond energy Csp 3

molecular orbitals. a C-C bond energy Csp 3

CC H H C H H C H H H H A model of ethylene using hybrid and atomic orbitals.

molecular orbitals. a C=C bond energy Csp 2

H H C H H C H H H H A model of ethene using hybrid and atomic orbitals. CC

H H C H H C CC HH H H

H H C H H C CC H HH H · · · · σ -bond π -bond

H H O C : : molecular orbitals. a C=O bond

A model of methyl aldehyde using hybrid and atomic orbitals. H H O C CO H HH H · · · · : :

In contrast to the rotation about single bonds, the rotation about double bonds is very difficult. energy 12 kJ C

2p x 2p z 2p y 2s

Important consequences of Quantum Mechanics The locations of the electrons are described The locations of the electrons are described by atomic orbitals. by atomic orbitals. A given orbital can contain only 2 electrons. (Pauli exclusion principle.) Atomic orbitals on different atoms will can combine to give molecular orbitals, but only if their symmetry matches. Each orbital has an associated energy and electrons will occupy the lowest energy orbitals first. good  bond bad – wrong symmetry No bonding! No bonding!

C, N, O s orbital p orbitals H x y z These atomic orbitals and their hybrids will be used extensively in our models of chemical bonding.

Common hybrid orbitals used in bonding of carbon, nitrogen and oxygen. sp x y z 2s 2p z 2p x 2p y

Common hybrid orbitals used in bonding of carbon, nitrogen and oxygen. sp hybrid orbital angle 180° sp sp pzpzpzpz pypypypy2s 2p z 2p x 2p y

Common hybrid orbitals used in bonding of carbon, nitrogen and oxygen. sp 2 2s 2p z 2p x 2p y hybrid orbital angle 120° pzpzpzpz

Common hybrid orbitals used in bonding of carbon, nitrogen and oxygen. sp 3 2s 2p z 2p x 2p y hybrid orbital angle 109.5°

Methane sp 3 H H C H H H C sp3 -H s

Ethane sp 3 H H H C H

Ethane H C H H ● H H H C ●

Ethane H C H H H H H C ● ● C sp3 -H s C sp3 -C sp3

Ethane sp 3 C sp3 -H s C sp3 -C sp3