Electronic configuration

The electronic configuration of lanthanoids is $\mathrm{[Xe]\ 4f^{0\text{-}14}\ 5d^{0\text{-}2}\ 6s^2}$. This is because $\mathrm{1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6}$ is the electronic configuration of xenon, and we can simplify the electronic configuration of lanthanoids by writing $\mathrm{[Xe]\ 4f^{0\text{-}14} 5d^{0\text{-}2} 6s^2}$ (the book prints "writting"). The lanthanoids involve gradual filling of f-orbitals. The energies of the 5d and 4f orbitals are very close. For lanthanum, 4f is slightly higher in energy than 5d: lanthanum has the electronic configuration $\mathrm{[Xe]6s^2 5d^1}$, and not $\mathrm{[Xe]6s^2 4f^1}$. Gadolinium (Gd) and lutetium (Lu) have a $\mathrm{5d^1}$ electron, to make the f-orbital half-filled and full-filled, which renders them extra stability. The electronic configurations of lanthanoids have variable occupancy in the 4f (0 to 14) orbitals. This can be noticed from Table 8.11. The number of electrons in the 6s orbitals remains constant in the ground state. The valence shell electronic configuration of these elements thus can be represented as: $\mathrm{(n-2)f^{\,0,2\text{-}14}\ (n-1)d^{\,0,1,2}\ ns^2}$

The electronic distribution in different orbitals of elements in their ground and excited states are shown in Table 8.11.

Ionization Enthalpies

The ionization enthalpies of lanthanoids are given in Table 8.12.

Table 8.12: First, second, third and fourth ionization enthalpies of lanthanoids in kJ/mol