AP chem unit 10 Hybridization

• More bonds = ---- full orbitals = ----- stability

more, more

• Hybrid orbitals will overlap on axis with orbitals from --------. • Unhybridized p orbital will overlap ------, or side by side, with an unhybridized p orbital of another atom.

other atoms , sideways

The second bond of a double bond results from the interaction of electrons in p-orbitals that are at right angles from the internuclear axis. This type of bond is known as a------. The greatest electron density of a pi bond is above and below the axis between the nuclei of the bonding atoms.

pi bond, π

The geometry of the overlapping orbitals determines the ----- of the molecule.

shape

• One bond is formed from the interactions of electrons that are between the two nuclei. The electron density of this bond is greatest along the axis between the two nuclei. This type of bond is called a ---------.

sigma bond, σ

Valence Bond Theory: Main Concepts

1. The valence electrons of the atoms in a molecule reside in quantum-mechanical atomic orbitals. The orbitals can be the standard s, p, d, and f orbitals, or they may be hybrid combinations of these. 2. A chemical bond results when these atomic orbitals interact and there is a total of two electrons in the new molecular orbital. • The electrons must be spin paired. 3. The shape of the molecule is determined by the geometry of the interacting orbitals

pi bonds

A pi (p) bond results when the bonding atomic orbitals are parallel to each other and perpendicular to the axis connecting the two bonding nuclei. • Between unhybridized parallel p orbitals • The interaction between parallel orbitals is not as strong as between orbitals that point at each other; therefore, s bonds are stronger than p bonds.

hybridized atomic orbitals

These orbitals are hybridized atomic orbitals, a kind of blend or combination of two or more standard atomic orbitals.

Valence Bond theory

approaches chemical bonding based on an extension of the quantum-mechanical model. • When orbitals on atoms interact, they make a bond

Orbital Diagrams of Bonding

• "Overlap" between a hybrid orbital on one atom with a hybrid or nonhybridized orbital on another atom results in a s bond. • "Overlap" between unhybridized p orbitals on bonded atoms results in a p bond. • Hybrid orbitals overlap to form a s bond. Unhybridized p orbitals overlap to form a p bond.

sigma bond

• A sigma (s) bond results when the interacting atomic orbitals point along the axis connecting the two bonding nuclei. • Either standard atomic orbitals or hybrids • s to s, p to p, hybrid to hybrid, s to hybrid, etc

Hybridization Geometry

• All 4 bonds of carbon are equivalent in energy, so it seems the 4 atomic orbitals (1 s orbital and 3 p orbitals) hybridize into 4 equivalent molecular orbitals, which we call sp3 hybridization. • The geometry of sp3 hybridization is Tetrahedral = 109.5o bond angles

sp3 Hybridization

• Atom with four electron groups around it • Tetrahedral geometry • 109.5° angles between hybrid orbitals • Atom uses hybrid orbitals for all bonds and lone pairs.

sp Hybridization

• Atom with two electron groups; for example C2H2 • Linear shape, 180° bond angle • Atom uses hybrid orbitals for s bonds or lone pairs and uses nonhybridized p orbitals for p bonds • Usually will form two s bonds and two p bonds

Preparing for Bonding

• Atoms use their valence orbitals to form bonds. • Since bond formation releases energy, atoms tend to form as many bonds as possible

Bond Rotation

• Because the orbitals that form the s bond point along the internuclear axis, rotation around that bond does not require breaking the interaction between the orbitals. • But, the orbitals that form the p bond interact above and below the internuclear axis, so rotation around the axis requires the breaking of the interaction between the orbitals.

sp2 Hybridization

• Hybrid orbitals will overlap on axis with orbitals from other atoms. • Unhybridized p orbital will overlap sideways, or side by side, with an unhybridized p orbital of another atom.

Hybridization

• Some atoms hybridize their orbitals to maximize bonding. • Hybridizing is mixing different types of orbitals in the valence shell to make a new set of degenerate orbitals. • sp, sp2 , sp3 , sp3d, sp3d2 • The same type of atom can have different types of hybridization. • C = sp, sp2 , sp3

Hybrid Orbitals

• The number of standard atomic orbitals combined = the number of hybrid orbitals formed. • Combining a 2s with a 2p gives two 2sp hybrid orbitals. • H cannot hybridize! • Its valence shell has only one orbital. • The particular kind of hybridization that occurs is the one that yields the lowest overall energy for the molecule

Sigma bonds use the hybridized orbitals. Pi bonds use nonhybridized p orbitals.

• When a carbon atom has one double bond and two single bonds, one of the bonds is a pi bond and the other three bonds are sigma bonds. • The pi bond uses the p orbitals. • The 3 sigma bonds determine the trigonal planar geometry of the resulting molecule, and this carbon is sp2 hybridized.