Consider the following changes.
M(s)→M(g) .....(i)
M(s)→M2+(g)+2e− .....(ii)
M(g)→M+(g)+e−. .....(iii)
M+(g)→M2+(g)+e−. .....(iv)
M(g)→M2+(g)+2e− .....(v)
The second ionization energy of M can be calculated from the energy values associated with: