Stability of the species `Li_(2), Li_(2)^(-)` and `Li_(2)^(+)` increases in the order of

Options

A. `Li_(2)^(-) lt Li_(2) lt Li_(2)^(+)`
B. `Li_(2) lt Li_(2)^(+) lt Li_(2)^(-)`
C. `Li_(2)^(-) lt Li_(2)^(+) lt Li_(2)`
D. `Li_(2) lt Li_(2)^(-) lt Li_(2)^(+)`

Answer

C

Explanation

`Li_(2) sigma (1s)^(2) sigma^(**) (1s)^(2) sigma (2s)^(2)` ,
Bond order ` = (1)/(2) (4-2) = 1 `
`Li_(2) ^(+) sigma (1s)^(2) sigma^(**) (1s)^(2) sigma (2s)^(1)` ,
Bond order `= (1)/(2) (3-2) = (1)/(2)`
`Li_(2)^(-) sigma (1s)^(2) sigma^(**) (1s)^(2) sigma (2s)^(2)(2s)^(1) `,
Bond order = `(1)/(2) (4-3) = (1)/(2)`
`LI_(2)^(-)` is less stable than ` Li_(2)^(+)` because ` Li_(2)^(-)` has more
number of electrons in the antibonding molecular
orbitals . Otherwise greater the bond order , greater
is the stability . Hence , the correct order is
`Li_(2)^(-) lt Li_(2)^(+) lt Li_(2) ` .