Isoelectronic ions

Much of the chemistry of oxygen can be rationalized in terms of its electronic structure (2s 2p ), high electronegativity (3.5) and small size. Thus, oxygen shows many similarities to nitrogen (p. 412) in its covalent chemistry, and its propensity to form H bonds (p. 52) and p double bonds (p. 416), though the anionic chemistry of 0 and OH is much more extensive than for the isoelectronic ions N , and NH2. Simi-... 

There is an interesting similarity in the character of the solution absorption spectra of the isoelectronic ions Np3+ and Pu1 even though the absorption bands in Pu1 + are all shifted toward higher energies due to increases in both the electrostatic (Fk) and spin-orbit ( ) parameters, Table VI. We have also examined the spectra of complex alkali-metal Pu(IV)... 

SOLUTION The smaller member of a pair of isoelectronic ions in the same period will be an ion of an element that lies farther to the right in a period, because that ion has the greater effective nuclear charge. If the two ions are in the same group, the smaller ion will be the one that lies higher in the group, because its outermost electrons are closer to the nucleus. Check your answer against the values in Appendix 2C. 

In accordance with previous investigations [8,9], Aese experiments have shown a quite different behaviour for N (ls )than for other multicharged ions such as the isoelectronic ion [10. The single-electron capture process has been shown to be dominant on the n = 3 levels and in particular on the 3s level for collision energies lower than 50 keV. A high probability of double capture has also been observed characterized by an intense peak at X = 76.5 nm attributed to the 2s > 2s 2p P transition [4,5,7]. Furthermore,... 

Two-electron systems, i.e. the He atom and its isoelectronic ions, are the simplest species exhibiting electron correlation, and ever since the earliest days of quantum mechanics there has been interest in finding simple, yet accurate descriptions of correlation effects in such systems. Independent-particle... 

If the electron-cloud radius yrms were exactly equal to the structural radius r, Wasastjerna s criterion would be obviously true. But in fact, for ions r ce. 2 yrms (Table 3). Hence the criterion needs justification. It is obviously most probable for isoelectronic ions (cp. Eauling (/)), but the electron-cloud radii should refer to the ions in the crystals, not to the free ions. For, with a gross difference between crystal and free-ion electron-cloud radii for the hydride ion, there may be significant differences for others 40). For the crystals the electron-cloud radii could be obtained either from polarizeability or from magnetic susceptibility. The theory of polarizeability is less certain and there is a considerable correction to infinite wavelength. We therefore adopt the magnetic evidence. But this must be corrected for the inner shell contribution (Table 3). 

The vibrational spectra of SJN" ( N = 30% N) suggest an SNSS or unbranched arrangement of atoms in the anion in contrast to the well established branched structure (Dj ) of the isoelectronic ion. Thus only one band is... 

In order to analyze the performance of the I-MZ purification procedure and to compare it with the MZ one, a set of calculations have been carried out. The probes selected have been the beryllium atom, the isoelectronic ions B" ",... 

This is supported by comparison with the isoelectronic ion SO3, which has an isotropic g tensor at 2.0036 in K2CH2(S03)2 (376), C103, which exhibits an axial g tensor (gL = 2.008, g = 2.007) in NH4C104 (377), and POr (gL = 2.001, gn = 1.999) in Na2HP03-5H20 (378). However, on surfaces there are only two reports of 25-electron radicals adsorbed on surfaces. SO3 adsorbed at the surface of MgO gives an isotropic signal with... 

Fluoride ion tends to replace the isoelectronic ion OH- in solids. In particular, hydroxyapatite, Cas O OH, the chief constituent of tooth enamel, reacts slowly with aqueous fluoride to form fluoroapatite, which is harder and more resistant to tooth decay. The dental profession therefore advocates fluoride treatments at the time of regular dental checkups, and also (primarily to provide for the dental health of children) the presence of 0.7-1.0 ppm natural or added F in drinking water. Too much (>4 ppm) F in water, however, is acknowledged to cause mottling of teeth and bone sclerosis. Thus, the range of concentrations over which fluoride in public drinking water is considered to be beneficial is rather narrow. 

The spectra of a number of triatomic radicals with 15 valence electrons are now known for elements of the first period they are B02, N3, and NCO. In addition, the isoelectronic ions C02+ and N20+ have been investigated. The spectrum of B02 was observed by Johns41 in the flash photolysis of a mixture of BCI3 and 02, but later was found to be identical to the green bands observed in most flames and arcs containing boron.42 Isotope shifts (B1X-B10) and alternate missing lines in the spectrum immediately identify the carrier as... 

Table 3.3 gives a compilation of ionic radii. It is seen that for isoelectronic ions the radius decreases as the net positive charge increases. In relation to the periodic table this means that ion size decreases from left to right in a period. This is due to the same factors that make the ionization potential increase electrons are held more tightly and thus move closer to the nucleus. Going down a periodic family, we find that the increasing principal quantum number and the increased screening by core electrons produce an increase in ionic size. 

It is instructive to consider the Stokes shift of the emission. It depends on the coupling parameter S like the occurrence of vibrational structure does. Table 3 shows for three different 5s2 ions, Sn2+, Sb3+ and Te4+, in comparable host lattices the Stokes shift and the value of the spin-orbit coupling constant [19]. The luminescent ions have practically the same size as the host lattice ions involved. It is clear from the table that the Stokes shift increases drastically in the sequence of isoelectronic ions Te4+ [Pg.13]

The atomic radii of isoelectronic ions and their neutral atoms are not equal because their nuclei have different numbers of protons. 

Since more protons means more attraction, more protons in the nuclei of isoelectronic ions or atoms have a smaller atomic radius. 

The atomic radii of isoelectronic ions are given here. As is easily seen, they radii become smaller as their atomic numbers (the charges of the nuclei) increase. 

In this section we discuss another family of high-symmetrical strained clusters in which the icosahedral aluminum "subcluster" AI12 with diameter 5.2 A and with a "dopant" atoms L or isoelectronic ions in the center (L = B-, C, N+, Al-, and Si), is inserted into the dodecahedral cage Al2o03o with diameter 9.5 A (Figure 8). All calculations were performed at the B3LYP/6-31G level [61]. 

Isoelectronic Ions Ions which have the same number of electrons are called isoelectronic ions, i.e. O2-, Na+, Al3+ and Ne all have 10 electrons so they are isoelectronic. 

Sizes of ions related to positions of elements in the periodic table. Note that size generally increases down a group. Also note that in a series of isoelectronic ions, size decreases with increasing atomic number. The ionic radii are given in units of picometers. 

One trend worth noting involves the relative sizes of a set of isoelectronic ions—ions containing the same number of electrons. Consider the ions O2-, F, Na+, Mg2+, and Al3+. Each of these ions has the neon electron configuration. How do the sizes of these ions vary In general, there are two important facts to consider in predicting the relative sizes of ions the number of electrons and the number of protons. Since these ions are isoelectronic, the number of electrons is 10 in each case. Electron repulsions should therefore be about the same in all cases. However, the number of protons increases from... 

For isoelectronic ions, size generally decreases as 1 increases. 

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