Chemistry last unit for final

Valence Shell Electron Pair Repulsion (VSEPR Model)

The shape around an atom is determined primarily by minimizing electron repulsions at the valence level

Hybridization

Molecular orbitals are modeled as forming from atomic orbitals that have been mathematically recombined to give an equivalent number of hybrid orbitals w/ the observed molecular shape

If the e^- group geometry is LINEAR…. what’s the hybridization?

sp

If the e^- group geometry is TRIGONAL PLANAR…. what’s the hybridization?

sp2

If the e^- group geometry is TETRAHEDRAL…. what’s the hybridization?

sp3

If the e^- group geometry is TRIGONAL BIPYRAMIDAL…. what’s the hybridization?

sp3d

If the e^- group geometry is OCTAHEDRAL…. what’s the hybridization?

sp3d2

Sigma Bonds

Molecular orbitals on the bond axis (line connecting two nuclei)

There’s always ONE sigma bond present with each bond (single = 1, double = 1, triple = 1)

stronger than pi bonds

Pi Bonds

Sideways overlap of parallel atomic p-orbitals (they are formed from p-orbitals)

weaker than sigma bonds

Increases with each additional bond (single = 0, double = 1, triple = 2)

Limitations to Localized-electron Models of Bonding

They are entirely qualitative and don’t say anything about orbital energies

Electrons are not actually localized (we needed to use resonance structures as a work around)

Localized models ignore empty orbitals

Molecular orbital (de-localized) Model of Bonding

When two waves combine, they interact in two different ways:

Waves add in-phase and constructively interfere

They also add out of phase and destructively interfere

When two new orbitals combine, two new orbitals form so they either….

Combine constructively, giving a bonding orbital

Or combine destructively, giving an antibonding orbital

Bonding orbital is made from …

Constructive combining

Antibonding orbital is made from…

Destructive combining

Electrons in a bonding orbital (not antibonding) are strongly associated with….

Two nuclei meaning it’s overall lower in energy

Electrons in a Antibonding bonds are pushed away from….

the nuclei which makes them higher in energy than normal orbital bonds

The sigma orbital is a bonding orbital because …

putting electrons in the orbital draws the nuclei together

The sigma star orbital is antibonding because…

putting electrons there pulls the nuclei apart

(antibonding = - + + - (electrons favor outside and pulls them apart = higher energy)

How to find bond order

(Number of bonding electrons - Number of antibonding electrons)/2

Paramagnetic

If a molecule has any unpaired electrons (would stick to a magnet)

Diamagnetic

When all electrons are paired

Sigma and Pi when they have a star

They are out of phase and destroy eachother/push eachother apart

Sigma and pi when they don’t have a star

They build eachother up in nuclei area = attraction

Molecular Orbitals in Heteronuclear Diatomic Molecules

Where atomic orbitals are similar but not identical, the MO diagram is similar to the homonuclear examples (like CN^-)

Molecular orbitals are more like the atomic orbitals they are ….

energetically closer to

Waves affect each other when they are….

similar size, shape, and energies

Elements that are very different from one another have very different…

valence electrons, so their orbitals do not affect each other very much (like HF)

Ions are attracted to one another by strong…

electrostatic (+ likes -) = like ionic bonds

Intermolecular forces are forces…

between molecules

Intramolecular forces are…

are bonds!

Dipole-Dipole

Forces exist between polar molecules (like PF3)

Hydrogen Bonds

Special type of dipole-dipole force