HybridizationQuantum Mechanics and Bonding

Overlap and Bonding

○ Covalent bonds form through the sharing of electrons by adjacent atoms.

○ Can only occur when orbitals on the two atoms overlap.

Valence Bond Theory

○ The atomic orbitals overlap to form a new orbital with a pair of opposite-spin electrons

Valence Bond Theory○ Overlap brings the electrons and nuclei

closer together○ Decreases electron-electron repulsion.

○ If atoms get too close, the internuclear repulsion raises the energy.

Yes

Cl2 forms from overlap with two 3p orbitals

F2 forms from overlap with two 2p orbitals

Smaller than 3p orbitals.

Hybrid Orbitals

It’s hard to imagine tetrahedral, trigonal bipyramidal, and other geometries from the atomic orbitals we have learned.

Hybrid Orbitals

○ Consider beryllium:● In its ground electronic state, it would not

be able to form bonds.● It has no singly-occupied orbitals.

Hybrid Orbitals

By absorbing a small amount of energy, an electron can be promoted from the 2s to the 2p orbital.

It can now form two bonds!

Hybrid Orbitals

○ Mixing the s and p orbitals creates two hybrid orbitals.● These sp hybrid orbitals have two lobes like a p orbital.

● One of the lobes is larger and more rounded as is the s orbital.

Hybrid Orbitals

○ These two degenerate orbitals would align themselves 180° from each other.

○ This is consistent with the observed geometry of beryllium compounds: linear.

Hybrid Orbitals

○ With hybrid orbitals the orbital diagram for beryllium would look like this.

○ The sp orbitals are higher in energy than the 2s orbital but lower than the 2p.

2s

Hybrid Orbitals

Using a similar model for boron leads to…

Hybrid Orbitals

…three degenerate sp2 orbitals.

Hybrid Orbitals

With carbon we get…

Hybrid Orbitals

…four degeneratesp3 orbitals.

The unhybridized p-orbital is perpendicular to the plane of the sp2 orbitals.

Hybrid Orbitals

For geometries involving expanded octets on the central atom, we must use d orbitals in our hybrids.

Hybrid Orbitals

This leads to five degenerate sp3d orbitals…

…or six degenerate sp3d2 orbitals.

Hybrid Orbitals

Once you know the electron-domain geometry, you know the hybridization state of the atom.

All you need to know about orbital hybridizationValence shell atomic orbitals (including inner

valence d orbitals) on two atoms overlap to produce covalent bonds.

Atomic orbitals hybridize to produce orbitals of equal energy with spatial orientations that can be predicted by VSEPR theory.

--based on ELECTRON DOMAIN GeometryLinear tri-plan tetra tri bypyr octa2 = sp 3 = sp2 4 = sp3 5 = sp3d 6 = sp3d2

Which kind of hybridization is about the central atom in PCl5?1. sp2

2. sp3

3. sp4

4. sp3d

Correct Answer:1. sp2

2. sp3

3. sp4

4. sp3d

The hybridization for PCl5 is sp3d, as shown to the right.