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:. Sigma ( σ ) Bonding. When bonding occurs along a bond axis, it is referred to as a “ sigma ” bond: ( ) The electrons occupy space between the nuclei. X. Y. :. X Y. Pi ( π ) Bonding.

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sigma bonding

:

Sigma (σ) Bonding

When bonding occurs along a bond axis, it is referred to as a “sigma” bond: ()

The electrons occupy space between the nuclei.

X

Y

pi bonding

:

X Y

Pi (π) Bonding

When bonding occurs above and below a bond axis, it is referred to as a “pi” bond: ()

The electrons occupy space above and below the nuclei.

slide3

:

X Y

:

Sigma (σ) Bonding & Pi (π) Bonding

Sigma () bonding: When bonding occurs along a bond axis, it is referred to as a “sigma” bond.

Pi () bonding: When bonding occurs above and below a bond axis, it is referred to as a “pi” bond.

A double bond is made up of a  and a  bond.

hybridization of atomic orbitals
Hybridization of Atomic Orbitals

The simple model of atomic orbital overlap in H2, HF and F2 breaks down for more complicated molecules.

Consider methane: VSEPR theory predicts bond angles of 109.5°.

These angles can’t be achieved with the s, px, py & pz orbitals of the central carbon atoms.

slide5

2p



2s

carbon

Hybridization of Atomic Orbitals

In order to attain the needed geometry, the atomic orbitals (AO’s) mix orhybridizeto form new valence bondorbitals.

consider carbon as a central atom in a molecule:

The valence orbitals are the 2s & 2p’s

There are 4 valence electrons:

slide6

Hybridization of Atomic Orbitals

This hybridization determines by the electron pair geometry for the central atom.

Each half-filled orbital is capable of forming a covalent bond.

The new orbitals are called

sp3

Valence bondorbitals

2p

carbon



2s

carbon

The 4 valence electrons on carbon fill the orbitals by Hund’s rule:

slide8

sp3Hybridization

Conclusion:

When the central atom in a molecule has combination of 4 total sigma (single) bonds and lone pairs, the hybridization at the central atom is sp3.

slide9

sp2Hybridization

Comes from mixing one ____________ AO

with two _____________ Aos. They hybridize to form new valence bondorbitals or “molecular orbitals (MOs)

there is one p-orbital left over

2p

The new hybrid obitals all have the same energy:

sp2

The new orbitals are called sp2Valence bondorbitals

slide11

sp2Hybridization

The remaining p-orbital is perpendicular to the three sp2 valence bond orbitals that spread out in a plane.

slide12

sp2Hybridization

Bonding in BF3

The atomic orbitals on the central B-atom can’t accommodate 3 bonds!

bonding in bf 3
Bonding in BF3

The 1 s orbital and 2 p orbitals must mix to form 3 new sp2 hybrid orbitals.

The 3 sp2 hybrid orbitals can now form sigma bonds with each half-filled p-orbital on each fluorine atom.

This results in a “Trigonal Planar” molecular and electron pair geometry.

slide14

sp2Hybridization

Bonding in an sp2hybridized atom is shown below:

Each of the three sp2 orbitals can form a -bondwith another atom.

Two of the orbitals overlap along the bond axis:

“end on” overlap

The left over p-orbital can form a -bondwith another half-filled p-orbital.

results in a -bond!

“Sideways” overlap...

slide15

sp2Hybridization

Bonding in an sp2hybridized atom is shown below:

Each of the three sp2 orbitals can form a -bondwith another atom.

Two of the orbitals overlap along the bond axis:

“end on” overlap

The left over p-orbital can form a -bond with another half-filled p-orbital.

results in a -bond!

“Sideways” overlap...

slide16

sp2Hybridization

An example of sp2 hybridization is given by C2H4 (ethene)

The left over p-orbitals on each carbon overlap to form the -bond (second half of the double bond).

Each sp2 orbital can form a -bond, two with each of the H’s and one with the other carbon.

2p

2p

Carbon

sp2 hybrid valence bond orbitals.

H

H



Trigonal planar EPG at each carbon: sp2hybridizaton!

C

C

2s

H

H

bonding in c 2 h 4
-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.

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.

slide23

Other Examples of Molecules with sp2: CH2O

Conclusion: When a central atom has a trigonal planarelectronic geometry (EPG), it is most likely to bond through sp2 hybridization.

Compounds containing double bonds ( + ) most often have have sp2 hybridization.

slide24

2p

2p

sp hybrid valence bond orbitals form.

2s

sp Hybridization

A mix of ________________ and ___________ .

The sp orbitals spread out to form a linear geometry (directed away from one another) leaving the unused p-orbitals perpendicular to the molecular axis.

The sp orbitals can form -bonds or hold lone pairs. The two unused p-orbitals can form the (2) -bondsin a triple bond.

An example of sp hybridization is given by C2H2 (acetylene)

Carbon



slide25

sp Hybridization

Just as with sp2 hybridization, in sp hybridization, the left over p-orbitals can form -bonds (in this case 2).

In acetylene (C2H2) there is a triple bond. (1 , 2 ’s)

slide27

sp Hybridization

Other examples of molecules with sp hybridization are:

N2

:NN:

CN– (cyanide anion)

[:CN:]–

Conclusion: When a central atom has a linear electronic geometry (EPG) with no lone pairs , it is most likely to bond through sp hybridization.

Compounds containing triple bonds ( + 2) or adjacent double bonds (CO2) have sp hybridization.

sp sp 2 sp 3 hybridization
sp, sp2, & sp3 hybridization

….has 2 leftover orbitalsavailable for triple bonding.

….has 1 leftover orbitals available for double bonding.

….has no leftover orbitals. sp3 allows single bonds only.