Hybrid Orbitals

Why Covalent Bonds Exist

Atoms share electrons when their orbitals overlap

When orbitals overlap, electrons are simultaneously attracted to both nuclei

Bond Length

As atoms come closer, increasing electron density results in a decrease in potential energy of system

As atoms become very close, electrostatic repulsion between nuclei increases

Bond distance is a compromise between increased overlap drawing them together and increased repulsion pushing them apart

There is an optimal bond distance where energy is lowest

Sigma Bond (σ)

Covalent bond which the electron density is concentrated symmetrically along the internuclear axis

Line joining the two nuclei passes through middle of overlap

Could be two s orbitals overlap, two p orbitals overlap or an s and p overlap

Pi Bond (π)

Overlap of orbital is perpendicular to line connecting nuclei

Two p orbitals overlapping Since not a total overlap pi bonds tend

to be weaker than sigma

Bond Types Single bonds are always sigma Double bonds consist of a sigma and a

pi bond Triple bonds, sigma and two pi

Hybrid Orbitals

Mixing of s and p orbitals creates hybrid orbitals

CH4 has four bonds coming from central atom

Each bond is formed by overlap of an sp hybrid orbital

Types of Hybrids

sp3 hybrid – one s and three p orbital joined

sp2 hybrid – one s and two p orbitals sp hybrid – one s and one p orbital Hybrid orbital type accounts for

observed geometry

Unshared Pairs

Unshared pairs can occupy hybrid orbital

NH3

H2O

Predicting Hybrid Orbitals

Draw structure Determine electron pair geometry Specify hybrid orbitals needed to

accommodate the electron pairs

Examples

What type of hybrid orbitals in– BeH2

– BF3

– NH2-

– SF4