Chapter 11.1: Valence Bond (VB) Theory and Orbital Hybridization

Flashcards from Chapter 11.1 of Chemistry: The Molecular Nature of Matter and Change.

Valence bond theory (VB theory)

A model that relates molecular shapes to orbital shapes through orbital overlap and hybridization

• Covalent bonds form in constructively interfering orbital overlaps, where electrons reside

• Overlapping regions are bound by the Pauli exclusion principle, with opposing spins

• Orbitals are reoriented to maximize overlap and strength, seen in p and d orbitals’ shapes

• Orbitals hybridize and form new hybrid orbitals to account for new behavior and properties

Hybridization

The formation of new hybrid orbitals from the combination of different valence orbitals, where:

• The number of orbitals formed is equal to the number of orbitals mixed

• The types of orbitals formed varies with the types of orbitals mixed

• The shape and orientation of hybrid orbitals maximizes its overlap between its composites

• The resultant orbitals have an energy level between the original composites

Serves best as a mathematical concept rather than a literal translation

sp Hybridization

The creation of new sp orbitals from electrons in an s orbital with a p orbital for linear shapes, through:

1. An electron from an s orbital being promoted to a higher-energy p orbital

2. The now-separate s and p orbitals hybridizing (mixing) to form new, half-filled sp orbitals

   • The unused p orbitals remain empty and in place

3. The presentation of these new orbitals to other atoms, now correctly shaped and available

sp² Hybridization

The creation of new sp² orbitals from electrons in s and p orbitals, explaining trigonal planar shapes

• For atoms that bond with three other atoms, an s electron is promoted to a higher-energy p orbital alongside another half-filled p orbital, creating three hybridized sp² orbitals to bond

• For molecules that need a lone pair, an entire s pair and two half-filled p orbitals are hybridized into three sp² orbitals (with one fully paired)

• Unused p orbitals remain empty and in place

sp³ Hybridization

The creation of new sp³ orbitals from electrons in s and p orbitals, explaining tetrahedral shapes

• For atoms that bond with four other atoms, an s electron is promoted to a higher-energy p orbital alongside two half-filled p orbitals, creating four hybridized sp³ orbitals to bond

• For atoms that require one or two lone pairs, an entire s pair alongside three p orbitals (one of which may be complete) is hybridized into four sp³ orbitals (with one or two fully paired)

sp³d Hybridization

The creation of new sp³d orbitals from electrons in s and p orbitals utilizing a d orbital as another promotion level, explaining trigonal bipyramidal shapes

• For atoms that bond with five other atoms, an s electron is promoted to a higher-energy d orbital above three half-filled p orbitals, creating five hybridized sp³d orbitals to bond

• For molecules that require a lone pair, a full p orbital promotes an electron to a higher-energy d orbital, allowing for a full s orbital and any remaining full p orbitals to be hybridized into five sp³d orbitals

sp³d² Hybridization

The creation of new sp³d² orbitals from electrons in s and p orbitals, utilizing 2 d orbitals as promotion levels to explain octahedral shapes

• For atoms that bond with six other atoms, two full lone pairs from the s and p levels each promote one electron to a d orbital, which then has all orbitals hybridize into sp³d² orbitals to bond

• For square pyramidal and square planar molecules, lone pairs also exist in these sp³d² orbitals after promotion

Draw the Lewis structure and determine the electron group arrangement and shape. Then, determine the hybrid orbital type from the specified arrangement.

How do I determine the type of hybrid orbitals present in a molecule?

Large nonmetal hydrides (like H₂S) due to longer bonds, and molecules with expanded valence shells due to d orbital instability.

Which two categories of molecules have limitations when examining them under VB theory?