lecture 5.8 - chemical bonding 6- hybridization
TRANSCRIPT
Chemical Bonding Chemical Bonding VI:VI:
Valence Bond Valence Bond TheoryTheory
& Orbital & Orbital HybridizationHybridization
Coordinate Covalent Bonds• A co-ordinate bond (also called a dative
covalent bond) is a covalent bond in which both electrons come from the same atom.
N H••
H
H
F B
F
F
+ F B
F
F
N H
H
H
Coordination Compounds
A coordination compound typically consists of a complex ion and a counter ion.
A complex ion contains a central metal cation bonded to one or more molecules or ions.
The molecules or ions that surround the metal in a complex ion are called ligands.
A ligand has at least one unshared pair of valence electrons
H
O
H
• • •• • •
H
N
HH• •
•• Cl
• •
••- ••C O••
Bonding Theories• Valence Bond (VB) Theory
• Molecular Orbital (MO) Theory
- MO theory no longer covered on AP Chem exam
Valence Bond Theory
• e- in a molecule occupy orbitals of the individual atoms
• Stable molecule form when P.E. of a system is minimized
• Atomic orbitals overlap to form bonds
• To accommodate bonds, valence orbitals of central atom combine or hybridize
H 1s H1s
H 1s H
A sigma bond (σ) forms as orbitals overlap
Sigma bond () – electron density between the 2 atoms
Hybridization – mixing of two or more atomic orbitals to form a new set of hybrid orbitals.
7
1. Mix at least 2 nonequivalent atomic orbitals (e.g. s and p). Hybrid orbitals have very different shape from original atomic orbitals.
2. Number of hybrid orbitals is equal to number of pure atomic orbitals used in the hybridization process.
3. Covalent bonds are formed by:
a. Overlap of hybrid orbitals with atomic orbitals
b. Overlap of hybrid orbitals with other hybrid orbitals
C + H
Carbon has only 2 unpaired electrons, it should form only 2 bonds to hydrogen.
Carbon actually forms 4 bonds to
hydrogen.
How??
Hybrid orbitals are energetically more favorable
Carbon Hybridization
Ene
rgy
2s
2p
2sp3
Carbon Hybridizati
on
Ene
rgy
Four sigma bonds forms + p + p + p = sp3
Formation of Covalent Bonds in CH4
Valence Bond Theory and NH3
N – 1s22s22p3
3 H – 1s1
If the bonds form from overlap of 3 2p orbitals on nitrogen with the 1s orbital on each hydrogen atom, what would the molecular geometry of NH3 be?
If use the3 2p orbitalspredict 90o
Actual H-N-Hbond angle is
107.3o
Predict correctbond angle
sp3-Hybridized N Atom in NH3
Need 2 bonding orbitals on S to bond with H.
H2S
sp3 Hybridization in H2S
σ bonds
Lone e- pairs
Predicting Hybridization of the Central Atom
1. Draw the Lewis structure of the molecule.
2. Count the number of lone pairs AND the number of atoms bonded to the central atom
( = STERIC NUMBER)
Steric # Hybridization Examples
2 sp BeCl2
3 sp2 BF3
4 sp3 CH4, NH3, H2O
5 sp3d PCl5
6 sp3d2 SF6
22
Formation of sp Hybrid Orbitals
24
Formation of sp2 Hybrid Orbitals
Hybridization for PCl5
1. Draw the Lewis structure of the molecule.
2. Determine Steric Number ( = # of hybrid orbitals)
Steric Number = 5So 5 orbitals must hybridize
s + p + p + p + d =
sp3d
Carbon Hybridizationsp3d Formation (in Phosphorus)
5 σ bonds can form
Carbon Hybridizationsp3d2 Formation (in Sulfur)
6 σ bonds can form
Pi Bonds ()• e- in unhybridized p orbitals overlap to form
bonds• e- density above and below plane of nuclei of the
bonding atoms
Ozone (O3)
35
Sigma bond () – electron density between the 2 atoms
Pi bond () – electron density above and below plane of nuclei of the bonding atoms
Bonding in Ethylene, C2H4
36
Sigma () and Pi Bonds ()
Single bond 1 sigma bond
Double bond 1 sigma bond and 1 pi bond
Triple bond 1 sigma bond and 2 pi bonds
How many and bonds are in the acetic acid (vinegar) molecule CH3COOH?
C
H
H
CH
O
O H bonds = 6 + 1 = 7
bonds = 1
O
HC
H
How can we explain the bonding in formaldehyde?
Steric Number ?
3 sp2
sp2 Hybridization of Carbon
bond
How can we describe the bonding In acetylene?
45
sp Hybridization of Carbon
2 bonds
Valence Bond Model for Acetylene
NextIf this slide does not work go to http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/hybrv18.swf
HW p. 442 # 20, 22, 25 -29