LRSVDS CHEM110 Bond Types 1

Chapter 9 part 4: Bond Types Read: BLB 9.5–6

HW: BLB 9:50,55,57;

Sup 9:17

Know:

• molecular orbitals

• orbital hybridization

• sigma (!) bond

• pi (") bond

• localized vs delocalized pi bonds & resonance

When is Exam 2?? ________________ Where is my section taking the Exam? _______________________________

o Data sheet in packet will be provided o Bring:

! pencils, ! student ID ! and a calculator—NO text-programmable

calculators or wireless devices

LRSVDS CHEM110 Bond Types 2

Hybridization Summary

Problem: Can’t use atomic orbitals to describe bonding in molecules

Solution: make molecular orbitals by

mixing atomic orbitals (call them hybrid orbitals)

Two atomic orbitals mix to form _____ hybrid orbitals 1 x s + 1 x p 2 x sp Three atomic orbitals mix to form _____ hybrid orbitals 1 x s + 2 x p 3 x sp2 Four atomic orbitals mix to form _____ hybrid orbitals 1 x s + 3 x p 4 x sp3 Five atomic orbitals mix to form _____ hybrid orbitals 1 x s + 3 x p +1 x d 5 x sp3d Six atomic orbitals mix to form _____ hybrid orbitals 1 x s + 3 x p +2 x d 6 x sp3d2

Each hybrid orbital can accommodate 1 pair of electrons.

Use VSEPR to determine shape of hybrid orbitals:

the electron pairs will get as far from each other as possible.

LRSVDS CHEM110 Bond Types 3

Summary of Hybridization Types

The hybridization scheme can be deduced from the electron-pair geometry of the

molecule.

Number of

electron pairs

Atomic orbitals used

Hybrid type

formed

Electron-pair

geometry

Examples

2

s, p

two sp

linear

BeF2, HgCl2

3

s, p, p

three sp2

trigonal planar

BF3, SO3, CO3

2#

4

s, p, p,

p

four sp3

tetrahedral

CH4, NH3, H2O, NH4

+

5

s, p, p,

p, d

five sp3d

trigonal

bipyramidal

PF5, SF4, BrF3

6

s, p, p, p, d, d

six sp3d2

octahedral

SF6, ClF5, XeF4, PF6

#

LRSVDS CHEM110 Bond Types 4

Bond Types !-bond • results from head-on overlap of orbitals • electron density is symmetric about the

internuclear axis: density ___________ nuclei. Examples: where spx and spy are hybrid orbitals

s-s s-p s-spx

p-p spx-sp

y

LRSVDS CHEM110 Bond Types 5

Bond Types "-bond • results from sideways overlap of orbitals • electron density is _____________________

the internuclear axis.

Two p-orbitals

LRSVDS CHEM110 Bond Types 6

Bonding in Ethylene

EPG: HYBRIDIZATION: Bond angles:

C C

H

H

H

H

One C$C and two C$H bonds (on each

carbon) are formed using sp2 orbitals on

carbons. ( !- bonds)

One singly occupied p-orbital is left on each carbon:

1) p-orbital perpendicular to the molecular plane

2) overlap is _______________: "-bond

LRSVDS CHEM110 Bond Types 7

Orbital Theory of Bonding explains: • Why rotation about double bond does not occur • Why double bonds occur frequently with C, N, and

O but not with larger molecules

• stability of aromatic hydrocarbons

Alkene + Br2 reacts readily Aromatic + Br2: no reaction

" bonds of alkenes are very reactive toward

addition. (" bonds in alkynes even more so.)

"-bonds in benzene are NOT reactive due to the

extra stability of delocalized " system

LRSVDS CHEM110 Bond Types 8

Delocalized Bonding

EPG/MG : Hybridization:

N and O have singly occupied p-orbitals

Localized Bonding Delocalized Bonding

• Delocalized bonding brings added stability to

a molecule.

• Molecules with resonance structures have delocalized " bonding

O N

O

O

O N

O

O O

O

NO

LRSVDS CHEM110 Bond Types 9

Triple Bonds

Bonding in Acetylene; C2H2

How Many Total Bonds? ! "

LRSVDS CHEM110 Bond Types 10

Summary of Covalent bonding 1. Draw Lewis Structure

2. Use VSEPR to determine shape " e- pair geometry " molecular geometry

1. What hybrid orbitals are involved in bonding? Determined by electron pair geometry. (Know the shapes of the hybrid orbitals.)

4. Is the molecule polar? Determined by molecular geometry.

Remember: " Each single bond = covalent bond = ! bond

" A covalent bond forms when orbitals overlap.

!-bond: head-on overlap

"-bond: sidewise overlap

LRSVDS CHEM110 Bond Types 11

Practice Problems

1. Determine the hybrid orbitals on the nitrogen in angle 1 and the C in angle 2. Angle #1 Angle #2 A. sp

3 sp

2

B. sp2 sp

3

C. sp2 sp

D. sp3 sp

3

2. How many ! bonds in the molecule?

A. 5 B. 15 C. 8 D. 21

3. How many " bonds in the molecule?

A. 1 B. 4 C. 15 D. 2