Modern inorganic chemistry

15 The lanthanides and actinides

(Lanthanum to lutetium, actinium to lawrencium)

The element lanthanum (atomic number 57) has the electronic

configuration

La [Kr core] 4d^10 5s^2 5p*5dl6s^2

and appears as the first element of the third transition series. How-
ever, the next element, cerium (58) has the configuration

Ce [Kr core] 4dl°4f^1 Ss^2 5p*5dl6s^2

and the 4/quantum level fills up until lutetium (71) is reached:

Lu [Kr core] 4dl°4f"5s^2 5p*5dl6s^2

after which the filling of the 5d level is resumed. The elements from
lanthanum to lutetium are called the lanthanides. Similarly the
actinides begin at actinium (89),

Ac [Xe eore]4/^14 5J^10 6s^2 6p^6 6^7s^2

after which the 5f inner level begins to fill, until lawrencium(103) is
reached*:

Lw [Xe core] 4fl45d^10 5f^14 6s^2 6p^6 6d^1 7s^2

• These electronic configurations are formal; the orbitals in these heavy atoms
  are so close in energy that actual electronic configurations are very difficult to
  determine.
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