LECTURE 26- Molecular orbitals Arising Interaction of the 2s and 2p Atomic Orbitals

general order of filling the valence molecular orbitals for B2, C2, and N2

o2s< o*2s< pi 2py = pi 2pz< o2px< pi*2py = pi* 2pz< o*2px

general order of filling the valence molecular orbitals for O2, F2, and Ne2

o2s< o*2s< o2px< pi 2py = pi 2pz< pi*2py = pi* 2pz< o*2px

highest occupied molecu;ar orbital (HOMO)

highest energy MO from which an electron is first removed

lowest unoccupied molecular orbital (LUMO)

when an electron is added, the extra electron enters the MO of the lowest energy

frontier orbitals

HOMO + LUMO because they lie at the occupied-unoccupied frontier

B2 molecule

• VE: (O2s)²(o*2s)²(pi2py)^1(pi2pz)^1

• BO: ½ (4-2) = 1

• stable and exists

• paramagnetic: two unpaired electrons with parallel spins

C2 molecule

• VE: (O2s)²(o*2s)²(pi2py)^1(pi2pz)²

• BO: ½ (6-2)= 2

• stable and exists

• diamagnetic

N2 molecule

• VE: (O2s)²(o*2s)²(pi2py)^1(pi2pz)² (o2px)²

• BO: ½ (8-2) = 3

• stable and exists

• diamagnetic

O2 molecule

• VE: (O2s)²(o*2s)²(pi2py)^1(pi2pz)² (pi*2py)^1(pi*2pz)^1

• BO: ½ (8-4)=2

• stable and exists

• double bond: short O-O bond length and the relatively high bond energy

• paramagnetic: unpaired electrons

• lewis structure for O2 incorrectly implies that all the electrons are paired

O2- ion

• VE: (O2s)²(o*2s)²(pi2py)^1(pi2pz)² (pi*2py)²(pi*2pz)^1

• BO: ½ (8-5)= 1.5

• stable and exists

• paramagnetic

O2²- ion

• VE: (O2s)²(o*2s)²(pi2py)^1(pi2pz)² (pi*2py)²(pi*2pz)²

• BO: ½ (8-6)= 1

• stable and exists

• diamagnetic

O2 → O2^- → O2²-

bond length gets longer, but decreasing bond energies

F2 molecule

• VE: (O2s)²(o*2s)²(pi2py)^1(pi2pz)² (pi*2py)²(pi*2pz)²

• BO: ½ (8-6)= 1

• stable and exists

• diamagnetic

Ne2 molecule

• VE: (O2s)²(o*2s)²(pi2py)^1(pi2pz)² (pi*2py)²(pi*2pz)²(o*2px)²

• BO: ½ (8-8)= 0

• no bond and does not exist