1.

Bond order normally gives idea of stability of a molecular species. All the molecules viz. H_(2) Li_(2) and B_(2) have the same bond order yet they are not equally stable. Their stability order is

Answer»

`H_(2) GT B_(2) gt Li_(2)`
`H_(2) gt Li_(2) gt B_(2)`
`Li_(2) gt B_(2) gtH_(2)`
`B_(2) gt H_(2) gt Li_(2)`

Solution :The molecular orbital configuration of the given molecules is
`H_(2) = sigma2s^(2)` (no electron anti-bonding)
`Li_(2)= sigma 1s^(2) sigma ^(* *) 1 s^(2) sigma 2s^(2)` (two anti-bonding electrons)
`B_(2)=sigma 1s^(2) 1s^(2) sigma^(* *) 1s^(2) sigma 2s^(2) sigma^(* *) 2s^(2){pi 2p_(y)^(1)=pi2p_(z)^(1)}` (4 anti-bonding electrons)
THOUGH the bond order of all the species are same (B.O = 1) but stability is different. This is DUE to difference in the presence of no. of anti-bonding electron.
Higher the no. of anti-bonding electron lower is the stability hence the correct order is `H_(2) gt Li_(2) gt B_(2)`


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