Ch3: Bonding

Ionic Bonds

e transfer between atoms

Ions held together by electrostatic interactions

Covalent Bonds

e shared between atoms

Molecular Orbitals

2 atomic orbitals combining

\+/- wave functions

Bonding Orbital

Same wave function sign

Lower-energy (more stable)

Antibonding Orbital

Different wave function signs

Higher-energy (less stable)

Sigma Bond

Head-head or tail-tail atomic orbital overlap

Free rotation

Pi Bond

Side-side p orbital overlap (unhybridized)

Hinder rotation

Must exist with sigma bond

Weaker than sigma bond

Single Bond

1 sigma bond

Double Bond

1 pi bond + 1 sigma bond

Triple Bond

1 pi bond + 2 sigma bonds

Bond Length

More bonds = shorter bond

Short Bonds

Hold atoms closer together

Stronger than long bonds

Require more energy to break

Bond Strength

triple > double > sigma > pi

Hybrid Orbitals

Mix different orbital types

Make bonds to central atom equivalent

sp3 Hybridized

Tetrahedral (109.5%)

25% s character, 75% p character

Ex: CH4

sp2 Hybridized

Alkenes (120º separation)

33% s character, 67% p character

Unhybridized orbital = pi bond

sp Hybridized

Alkynes (180º separation)

50% s character, 50% p character

2 unhybridized orbitals = pi bonds

Resonance

Conjugated/partial bonds (alternate single and multiple bonds)

e delocalization in pi bonds

Increase stability

Conjugation

Single and multiple bonds alternate

System of unhybridized p orbitals down molecule backbone

Resonance True e Density

Weighted average of resonance structures

Favour most stable form

Resonance Stability

No formal charge

Form full octet on highly EN atoms

Stabilize charges with induction and aromaticity