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Chapter 9 . Bonding. Hybridization. Hybridization is the mixing of native atomic orbitals to form special orbitals for bonding.

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chapter 9
Chapter 9

Bonding

hybridization
Hybridization
  • Hybridization is the mixing of native atomic orbitals to form special orbitals for bonding.
  • Methane CH4- The carbon has a 2s and 2p(x,y,z) orbital filled with valence electrons. These should theoretically make 90 degree bonds with hydrogen but we find them to be 109.5 degrees.
  • This means that the 2s and 2p (x,y,z) orbitals combine to create the 4 new hybridized orbitals called sp3.
  • This gives us the tetrahedral shape.
  • We say the carbon atom undergoes sp3 hybridization or is sp3 hybridized.
in terms of energy

sp3

In terms of energy

2p

Hybridization

Energy

2s

sp 2 hybridization
sp2 Hybridization
  • Ethylene (C2H4)
  • Double bond acts as a single pair (chapter 8). Bond angles of 120 degrees.
  • 2s and 2p combined to form 3 sp2 orbital. Third p orbital is perpendicular to each hybridized orbital.
  • The 3 sp2 orbitals on each carbon are used to share an electron centered on a line running between atoms. This is known as a sigma (σ) bond.
  • The second part of the double bond results from sharing electrons in the space above and below the sigma bond. This uses the 3 perpendicular p orbital. This is known as a pi (π) bond.
sp hybridization
sp Hybridization
  • CO2
  • Involves one s and one p orbital to create two sp hybridized orbitals.
  • 2p orbital remains unchanged and are used for the 2 pi bonds.
  • The oxygen atom is sp2 hybridized.
  • Triple bonds always have 2 pi bonds and 1 sigma bond.
  • Double bonds always have 1 pi bond and 1 sigma bond.
dsp 3 and d 2 sp 3 hybridization
dsp3 and d2sp3Hybridization
  • Used when octet rule is exceeded.
  • dsp3 used when there are five pairs and a trigonalbipyramidal arrangement is needed.
  • d2sp3 is used when there are six pairs and a octahedral arrangement is needed.
  • Only sigma bonds no pi bonds.
the molecular orbital model
The Molecular Orbital Model
  • Atomic orbitals (chapter 7) are replaced by molecular orbitals (MOs).
  • MOs can hold two electrons with opposite spin.
  • Orbital properties of interest are size, shape, and energy.

H2

  • MO1 and MO2 created by the two hydrogen atoms.
  • MO1 greatest probability is between nuclei, MO2 is on either side of the nuclei. This is called a sigma molecular orbital.
the molecular orbital model1
In the molecule only the molecular orbitals exist, the atomic orbitals are gone

MO1 is lower in energy than the 1s orbitals they came from.

This favors molecule formation

Called a bonding orbital

MO2 is higher in energy

This goes against bonding

antibonding orbital

The Molecular Orbital Model
the molecular orbital model3
We use labels to indicate shapes, and whether the MO’s are bonding or antibonding.

MO1 = s1s

MO2 = s1s* (* indicates antibonding)

Can write them the same way as atomic orbitals

H2 = s1s2

Each MO can hold two electrons, but they must have opposite spins

Orbitals are conserved. The number of molecular orbitals must equal the number atomic orbitals that are used to make them.

The Molecular Orbital Model
slide11
H2-

s1s*

Energy

1s

1s

s1s

bond order
The difference between the number of bonding electrons and the number of antibonding electrons divided by twoBond Order