Why is the second ionisation energy of lithium much greater than that of beryllium?

The ionisation enthalpies of elements of the second period are given below:
Ionisation enthalpy $(\mathrm{kcal} {\mathrm{mol}}^{-1}): 520, 899, 801,1086, 1402, 1314, 1681, 2080$
Match the correct enthalpy with the elements and complete the graph given in the following figure. Also write the symbols of elements with their atomic numbers.

Consider the following changes:

(a) Sublimation energy of $\mathrm{M}=\mathrm{p}$

(b) Sublimation $\mathrm{E}+{\mathrm{IE}}_1+{\mathrm{IE}}_2$ of $\mathrm{M}=\mathrm{q}$

(c)  ${\mathrm{IE}}_1$ of $\mathrm{M}=\mathrm{r}$

(d)  ${\mathrm{IE}}_2$ of $\mathrm{M}=\mathrm{s}$

(e) ${\mathrm{IE}}_1+{\mathrm{IE}}_2$of $\mathrm{M}=\mathrm{t}$

The enthalpy change for the reaction ${\mathrm{M}}^{+}\left(\mathrm{g}\right)\to {\mathrm{M}}^{2+}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}$ could be calculated from the energy value associated with:

Successive ionisation energies of an element $\text{'}\mathrm{X}\text{'}$ are given below (in $\mathrm{k} \mathrm{cal}$): 

Electronic configuration of the element $\text{'}\mathrm{X}\text{'}$ is: