The Electronic Configurations of Elements Beyond Neon

The next elements are potassium and calcium, in which the outer electrons occupy the next lowest energy orbital, which is the 4s since it has a lower energy than the 3d orbitals in the two cases. In the next 10 elements (scandium to zinc) the five 3d orbitals are progressively occupied. The filling of the 3d orbitals is in accordance with Hund s rules, with two irregularities which are described below. 

The outer electronic configurations of the elements Sc, Ti and V are Sc 4s-3d, Ti 4s-3d-, V 4s-3d, but that of chromium is Cr 4s 3d. Regularity returns with the next four elements Mn 4s-3d, Fe 4s-3d Co 4s-3d, Ni 4s- 3d . With copper, the 3d level is sufficiently lower than the 4s to ensure complete pairing up in the 3d orbitals, leaving the sole unpaired electron in the 4s orbital Cu 4s 3d . The first series of transition elements is completed by zinc, which has the configuration 4s-3d °. 

Q Write down the values of the four quantum numbers of the electrons that may occupy 3d orbitals. 

Q Why are there ten groups of transition elements in the Periodic Table  

A Because the conclusions of the previous problem apply to any period with an n value of 3 or more. 

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