ORBITAL HYBRIDIZATION:The question of shape!

We need next to examine the relationship between:

• isolated atoms (with valence e’s in s,p, and d orbitals of specific shapes, see next slide as review!)

• bonded atoms in molecules or ions, in which bonded regions exhibit significantly different shapes as described by VSEPR theory

all s orbitals

all p orbitals

d orbitals

Orbital shapes, Individual (“isolated”) Atoms

Compare (next slide) to molecule, ion bonding shapes

trigonal tetrahedral

trigonal-bipyramidal octahedral

To rationalize how the shapes of atomic orbitalsare transformed into the orbitals occupied in covalently bonded species, we need the help oftwo bonding theories:

Valence Bond (VB) Theory, the theory we will explore,describes the placement of electrons into bonding orbitals located around the individual atoms from which they originated.

Molecular Orbital (MO) Theory places all electrons from atoms involved into molecular orbitals spread out over the entire species. This theory works well for excited species, and molecules like O2. You will meet this theory in advanced classes!

COVALENT BOND FORMATION (VB THEORY)

In order for a covalent bond to form between two atoms, overlap must occur between the orbitalscontaining the valence electrons.

The best overlap occurs when two orbitals are allowedto meet “head on” in a straight line. When this occurs,the atomic orbitals merge to form a single bonding orbital and a “single bond” is formed, called asigma () bond.

Dotted areas: representation of "electron cloud" for one electron

"Head-on Overlap"

Sigma Bond: merged orbital, 2 e's

MAXIMIZING BOND FORMATION

In order for “best overlap” to occur, valence electronsneed to be re-oriented and electron clouds reshapedto allow optimum contact.

To form as many bonds as possible from the available valence electrons, sometimes separation of electron pairs must also occur.

We describe the transformation process as “orbitalhybridization” and we focus on the central atom in the species...

“sp” Hybridization: all 2 Region

Species

BeCl2 BeCl ClBe 22Cl 14

16 e's/2= 8 prs

BeCl Cl (octet violator)

Number of regions around CENTRAL ATOM: 2

BeCl Cl shape : LINEARbond angles: 180o

Hybridization of Be in BeCl2

Atomic Be: 1s2 2s2

Valence e’s

2p

2s

Energy

separate 2p

2s

"hybridize"

"sp" "sp"

Hybrid sp orbitals:1 part s, 1 part p

"arrange"

(VSEPR)

BeBe is said to be "sp hybridized"

FORMATION OF BeCl2:

Each Chlorine atom, 1s22s22p63s23p5 , has one unshared electron in a p orbital. The half filled p orbital overlaps head-on with a half full hybrid sp orbital of the beryllium to form a sigma bond.

BeCl Cl

BeCl Cl

BeCl Cl

sp hybridized, linear, 180o bond angles

“sp2” Hybridization: All 3 Region Species

BF3 BF FB 33F 21

24 e's/2= 12 prs

BF F (octet violator)

Number of regions around CENTRAL ATOM: 3

shape : TRIGONAL PLANARbond angles: 120o

F

F

BF F

F

Hybridization of B in BF3

Atomic B : 1s2 2s2 2p1

Valence e’s

2p

2s

Energy

separate 2p

2s

"hybridize"

"sp2" "sp2" "sp2"

Hybrid sp2 orbitals:1 part s, 2 parts p

FORMATION OF BF3:

Each fluorine atom, 1s22s22p5, has one unshared electron in a p orbital. The half filled p orbitaloverlaps head-on with a half full hybrid sp2 orbitalof the boron to form a sigma bond.

"arrange"

(VSEPR)

BB is said to be "sp2 hybridized"

F F

sp2 hybridized, TRIGONAL PLANAR, 120o bond angles

B

F

F F

B

F

“sp3” Hybridization: All 4 Region Species

CH4

CH H

C 44H 4

Number of regions around CENTRAL ATOM: 4

shape : TETRAHEDRALbond angles: 109.5o

H

H

88 e's /2 = 4 pr

H

CHH

H

Hybridization of C in CH4

Atomic C : 1s2 2s2 2p2

Valence e’s

2p

2s

Energy

separate 2p

2s

"hybridize"

"sp3" "sp3" "sp3" "sp3"

Hybrid sp3 orbitals:1 part s, 3 parts p

FORMATION OF CH4:

Each hydrogen atom, 1s1, has one unshared electron in an s orbital. The half filled s orbitaloverlaps head-on with a half full hybrid sp3 orbitalof the carbon to form a sigma bond.

"arrange"

(VSEPR)C

C is said to be

"sp3 hybridized"

sp3hybridized, TETRAHEDRAL,

109.5o bond angles

C

H

H

H

H

C

H

H

H

H

Unshared Pairs, Double or Triple Bonds

Unshared pairs occupy a hybridized orbital the same as bonded pairs: See the example of NH3

that follows.

Double and triple bonds are formed from electronsleft behind and unused in p orbitals. Since allmultiple bonds are formed on top of sigma bonds,the hybridization of the single () bonds determinethe hybridization and shape of the molecule...

NH3 NH H

N 53H 3

8e's/2=4 prs

Number of regions around CENTRAL ATOM: 4

shape : TETRAHEDRALbond angles: < 109.5o

NH H

HNH H

H

H

Hybridization of N in NH3

Atomic N: 1s2 2s2 2p3

Valence e’s

2p

2s

Energy

"hybridize"

"sp3" "sp3" "sp3" "sp3"

FORMATION OF NH3:

Each hydrogen atom, 1s1, has one unshared electron in an s orbital. The half filled s orbitaloverlaps head-on with a half full hybrid sp3 orbitalof the nitrogen to form a sigma bond.

"arrange"

(VSEPR)N

N is said to be

"sp3 hybridized"

sp3hybridized, TETRAHEDRAL,

~107o bond angles

N

H

H

H

N

H

H

H

Describe Hybridization of C and shape of followingspecies: CO, CO2, HCN, CH2O, CO3

2- , CBr4

C O O C O H C N

O

C

HH

O

C

OO

2 Br

CBr

BrBr

“sp3d” Hybridization: All 5 Region Species

PF5P

F FP 55F 35

Number of regions around CENTRAL ATOM: 5

shape : TRIGONAL BIPYRAMIDALbond angles: 90, 120, 180o

F

F

4040 e's /2 = 20 pr

P

F

PF F

F

FF

F

F

F

F

F

Hybridization of P in PF5 P: 1s2 2s2 2p6 3s2 3p3

3p

3s

Energy

separate

3p

3s

"hybridize"

"sp3d" "sp3d" "sp3d" "sp3d"

3d 3d

"sp3d"

FORMATION OF PF5:

Each fluorine atom, 1s22s22p5, has one unshared electron in a p orbital. The half filled p orbitaloverlaps head-on with a half full hybrid sp3d orbitalof the phosphorus to form a sigma bond.

"arrange"

(VSEPR)

P is said to be

"sp3d hybridized"P

sp3d hybridized, TRIGONAL BIPYRAMIDAL,

90, 120, 180o bond angles

P

F

F

F

F

F

P

F

F

F

F

F

“sp3d2” Hybridization: All 6 Region Species

SF6S

F FS 66F 42

Number of regions around CENTRAL ATOM: 6

shape : OCTAHEDRALbond angles: 90, 180o

F

F48

48 e's /2 = 24 pr

S

F

SF F

F

F F

F

F

F

F

F

F

F

F

Hybridization of S in SF6 S: 1s2 2s2 2p6 3s2 3p4

3p

3s

Energy

separate

3p

3s

"hybridize"

"sp3d2"

3d 3d

FORMATION OF SF6:

Each fluorine atom, 1s22s22p5, has one unshared electron in a p orbital. The half filled p orbitaloverlaps head-on with a half full hybrid sp3d2 orbitalof the phosphorus to form a sigma bond.

"arrange"

(VSEPR)

S is said to be

"sp3d2 hybridized"S

sp3d hybridized, TRIGONAL BIPYRAMIDAL,

90, 120, 180o bond angles

S

F

F

F

F

F

S

F

F

F

F

F FF

Group Work 13.2

Describe hybridization of S and shape of speciesin SF2, SO2, SO3

2- , SF3+, SF4, SF5

-

S

F

FS

OO

S

OO

O

S

F

F F

2-

S

F

F

F

F

F

S

F

F

FF

Summary: Regions, Shapes and Hybridization

#, regions shape hybridization

2 linear sp

3 trigonalplanar

sp2

4 tetrahedral sp3

5 trigonalbipyramidal

sp3d

6 octahedral sp3d2

“BOTTOM LINE”

IF you can draw a Lewis structure for a species, and count electronic regions around central atom,you can immediately determine:

• the shape of the species about the central atom

• the hybridization of the species based on the central atom