Electronic configuration irregularities

The electron configurations of the first 20 elements are given in Table 17-6. The buildup principle is crudely analogous to filling an irregularly shaped vessel with marbles (see Fig. 17-9). The available spaces are filled from the bottom up. 

Krypton is an inert gas element. Its closed-shell, stable octet electron configuration allows zero reactivity with practically any substance. Only a few types of compounds, complexes, and clathrates have been synthesized, mostly with fluorine, the most electronegative element. The most notable is krypton difluoride, KrF2 [13773-81-4], which also forms complex salts such as Kr2F3+AsFe [52721-23-0] and KrF+PtFF [52707-25-2]. These compounds are unstable at ambient conditions. Krypton also forms clathrates with phenol and hydroquinone. Such interstitial substances are thermodynamicahy unstable and have irregular stoichiometric compositions (See Argon clathrates). 

The properties of the liquid lanthanide trihalides depend strongly on the atomic number of the halide. The variation in the heat capacity of the lanthanide fluorides indicates a strongly ionic behaviour of the melts with a concomittent irregular trend related to the electronic configuration of the lanthanide ions. In the lanthanide chlorides, bromides and iodides the trend becomes systematically more constant, indicating an increasing molecular nature of the melts. 

Several of the apparent irregularities in these electron configurations can be explained by the special stability of half-filled and filled sets of d orbitals (Section 5-17). 

The electron configurations in the second transition metal series [yttrium (Z = 39) to silver (Z = 47)] are also irregular, but we will not be concerned with the details here. 

Z4 Without referring to the text, write the ground-state electron configurations of the first-row transition metals. Explain any irregularities. 

Plan We first write the condensed electron configuration of the atom, noting the irregularity for Cr in (b). Then we remove electrons, beginning with ns electrons, to attain the ion charge. If unpaired electrons are present, the ion is paramagnetic. 

An important feature of these data is that I(r) does show a new inflection point starting at K that establishes the N shell, and another at Rb to begin the fifth shell. (For six of the elements in the second transition series, this last inflection point does not appear. This is presumably due, at least in part, to irregularities in the electronic configurations of these atoms Pd does not even have any fifth shell electrons and most of the others have only one [54,55].)... 

In the sequence of orbital energies shown above the 4s orbitals have a lower energy than the 3d orbitals and so they will be filled first in keeping with the minimum energy principle. For example, the electron configuration of the outer 10 electrons of calcium (atomic number Z = 20) is 3s 3p 3d 4s. In the filling of the electron orbitals for elements 21 to 29, there are two irregularities, one at 24 (chromium) and one at 29 (copper). Each of these elements contains one 4s electron instead of two. The reason... 

Understand how irregularities in the periodic trends for electron affinity can be related to electron configuration. (Section 7.5)... 

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