The electronic structure 10pts

1.) Explain why there is an enormous difference between
the third and the fourth ionization enthalpies of aluminium.

Aluminium has three outermost electrons. they are not stable because the outer shell is not fully filled. But for the forth electron, it is in a fully-filled shell which gives extra stability. So it takes enormoous energy to remove the forth electron

1.aluminium has 3 valence electrons. they are screened by the inner electrons and hence the effective nuclear charge is smaller.
the 4th electrons is located at the 2p subshell, whcih is completely filled. It has extra stability upon themselves. Also they are closer to the nucleus hence effective nuclear charge is higher. It accounts for the huge difference between the 3 and 4 I.E.
2. The difference in energy level at each consecutive principal quantum electron shells is becoming smaller and smaller. At n= infinity, the difference between the energy levle tends to become zero. Hence there is a converge limit