Give the electron configuration,bond order,magnetic property,and energy diagram for the Lithium $(Li_{2})$ molecule.

(N/A) $Li$ $(Z=3)$,so the total number of electrons in $Li_{2} = 6$.
Electron configuration in $MO$ for $Li_{2}$:
$(\sigma 1s)^{2} (\sigma^{*} 1s)^{2} (\sigma 2s)^{2}$ or $KK (\sigma 2s)^{2}$.
Magnetic Property: All electrons are paired,so it is diamagnetic.
Bond Order Calculation:
$N_{b} = 4$ (bonding electrons),$N_{a} = 2$ (antibonding electrons).
Bond order $= \frac{1}{2} (N_{b} - N_{a}) = \frac{1}{2} (4 - 2) = 1$.
Since the bond order is $1$,$Li_{2}$ has a single bond and is stable.
Note: $KK$ represents the core electrons $[He_{2}] = (\sigma 1s)^{2} (\sigma^{*} 1s)^{2}$.
The energy diagram for the $Li_{2}$ molecule is shown below: