Question

The following deviations in the series of electronic configurations are found in the Periodic Table.

Explain each deviation (both how and why they deviate).

Deviation series #1

Atomic # 40 Zr [Kr] 5s2 4d2

Atomic # 41 Nb [Kr] 5s1 4d4

Atomic # 42 Mo [Kr] 5s1 4d5

Atomic # 43 Tc[Kr] 5s2 4d5

Deviation series #2

Atomic # 56 Ba [Xe] 6s2

Atomic # 57 La [Xe] 6s2 5d1

Atomic # 58 Ce [Xe] 6s2 4f1 5d1

Atomic # 59 Pr [Xe] 6s2 4f3

Answer 1

Deviation series #1

Atomic # 40 Zr [Kr] 5s2 4d2

Atomic # 41 Nb [Kr] 5s1 4d4

Atomic # 42 Mo [Kr] 5s1 4d5

Atomic # 43 Tc[Kr] 5s2 4d5 ,Explained by the Extra stability of half or fully filled 'd' orbital ,that's why element show deviation

Deviation series #2

Atomic # 56 Ba [Xe] 6s2

Atomic # 57 La [Xe] 6s2 5d1

Atomic # 58 Ce [Xe] 6s2 4f1 5d1

Atomic # 59 Pr [Xe] 6s2 4f3 Here we need to know about the reason behind Ce ELECTRONIC CONFIGURATION --Cerium ,Pr,has a variable electronic structure. The energy of the 4f electron is nearly the same as that of the outer 5d and 6s electrons that are delocalized in the metallic state, and only a small amount of energy is required to change the relative occupancy of these electronic levels That's they show deviation. please see the properties of F- block element ,,

EXTRA POINT FOR THE ELECTRONIC CONFIGURATION The Aufbau principle states that, hypothetically, electrons orbiting one or more atoms fill the lowest available energy levels before filling higher levels (e.g., 1s before 2s). In this way, the electrons of an atom, molecule, or ion harmonize into the most stable electron configuration possible.

Electron behavior is elaborated by other principles of atomic physics, such as Hund's rule and the Pauli exclusion principle. Hund's rule asserts that even if multiple orbitals of the same energy are available, electrons fill unoccupied orbitals first, before reusing orbitals occupied by other electrons. But, according to the Pauli exclusion principle, in order for electrons to occupy the same orbital, they must have different spins.

The order in which these orbitals are filled is given by n+l rule known as Madelung Rule or diagonal rule.Orbitals with a lower (n+l) value are filled before those with higher (n+l) values where n represents principal quantum number and l represents azimuthal quantum number.

The fact that most of the ground state configurations of neutral atoms fill orbitals following this n + ℓ, n pattern was obtained experimentally, by reference to the spectroscopic characteristics of the elements.

The Madelung energy ordering rule applies only to neutral atoms in their ground state,even in some cases there are examples which show different electronic configuration than those of experimentally determined.Copper,Chromium and Palladium , Molybdenum and many other are common examples of this rule. THANK YOU VERY MUCH ,HOPE THIS WILL HELP YOU ,GOOD LUCK