Why #"Li"_2^+# is more stable than #"Li"_2# ?
According to J.D Lee, compounds with fraction bond number are unstable--
Li2+ BOND ORDER = 0.5 Li2 BOND ORDER =1 Hence Li2+ must be unstable than Li2 but then why Li2 is more stable than Li2+. Please explain reasons.
According to J.D Lee, compounds with fraction bond number are unstable--
Li2+ BOND ORDER = 0.5 Li2 BOND ORDER =1 Hence Li2+ must be unstable than Li2 but then why Li2 is more stable than Li2+. Please explain reasons.
1 Answer
No... it's the other way around.
Here we consider the molecular orbital diagram (MO) of
The bond order can be calculated in a simple manner. Just take electrons that are in each MO, and
- for each electron in a bonding MO, it adds
#0.5# to the bond order, because more bonding character strengthens the bond... - for each electron in an antibonding MO, it subtracts
#0.5# from the bond order, because more antibonding character weakens the bond...
Hence, the bond order of
#1/2 + 1/2 - 1/2 - 1/2 + 1/2 = 1# ,
indicating a single sigma bond (because they are in the
On the other hand,
#color(blue)("Bond order" ("Li"_2^+) = 0.5)#
And so, it has, hypothetically, half of a sigma bond. Clearly, half of a bond is less stable than one entire bond of the same type.