Question

justify the presence of 18 elements in 4th period of the periodic table.

Answer 1

When n = 4, These orbital 3d, 4s and 3p present as outermost shell shows the filling in order of their increasing energies in an order of 3p<4s < 4d . Now since the total number of orbitals available are 9 (i.e 1 from 4s, 3 from 3p and 5 from 3d orbital. Thus maximum number of electrons that can occupy theres three orbital are 18 thus we can say that 18 elements should be present in 4th period.