CHM 501 Lecture

First row diatomics: Li₂ to Ne₂

Note that 1* and 2 are close in energy and of the same symmetry () thus they can overlap (called a configuration interaction); overlap causes an energy change - an avoided crossing that changes the order of the orbitals:

X2	configuration	Bond Order	predicted spin	observed spin
Li2	12	1	0	0
Be2	121*2	0	0	-
B2	121*222	1	2	2
C2	121*24	2	0	0
N2	121*2224	3	0	0
O2	121*2224*2	2	2	2
F2	121*2224*4	1	0	0
Ne2	121*2224*42*2	0	0	-

Neither B₂ nor C₂ has bond, only bonds so the bond energies are quite low

Better:

Heteronuclear diatomics:

CO as an example (very important molecule in inorganic chemistry; it has the strongest homonuclear bond energy and is a very good Lewis base towards low valent metals)

basis set is still 2s, 2p but now the orbital energies are different

Hybridization to form sp hybrids gives required lone pairs and then form molecular orbitals

²1nb²⁴2nb²

BO = 3

valence orbital is a lone pair on C so the basic end is C