Shell, electron half-filled

If a shell Is half-filled, no electrons are paired in any orbitals. Pairing of electrons is allowed (with opposite spins), bat it still increases electron — electron repulsions. 

Carbon is central to life and natural intelligence. Silicon and germanium are central to electronic technology and artificial intelligence (Fig. 14.28). The unique properties of Group 14/IV elements make both types of intelligence possible. The half-filled valence shell of these elements gives them special properties that straddle... 

Although the role of rare earth ions on the surface of TiC>2 or close to them is important from the point of electron exchange, still more important is the number of f-electrons present in the valence shell of a particular rare earth. As in case of transition metal doped semiconductor catalysts, which produce n-type WO3 semiconductor [133] or p-type NiO semiconductor [134] catalysts and affect the overall kinetics of the reaction, the rare earth ions with just less than half filled (f5 6) shell produce p-type semiconductor catalysts and with slightly more than half filled electronic configuration (f8 10) would act as n-type of semiconductor catalyst. Since the half filled (f7) state is most stable, ions with f5 6 electrons would accept electrons from the surface of TiC>2 and get reduced and rare earth ions with f8-9 electrons would tend to lose electrons to go to stabler electronic configuration of f7. The tendency of rare earths with f1 3 electrons would be to lose electrons and thus behave as n-type of semiconductor catalyst to attain completely vacant f°- shell state [135]. The valence electrons of rare earths are rather embedded deep into their inner shells (n-2), hence not available easily for chemical reactions, but the cavitational energy of ultrasound activates them to participate in the chemical reactions, therefore some of the unknown oxidation states (as Dy+4) may also be seen [136,137]. 

For most atoms, the addition of an electron occurs with the release of energy, so the value of AE is negative. There are some exceptions, most notably the noble gases and group IIA metals. These atoms have completely filled shells, so any additional electrons would have to be added in a new, empty shell. Nitrogen also has virtually no tendency to accept an additional electron because of the stability of the half-filled outer shell. 

The electron affinity of nitrogen is out of line with those of other atoms in the same period because it has a stable half-filled shell. 

Whereas nitrogen has an electron affinity that is approximately zero, phosphorus has a value greater than zero even though it also has a half-filled outer shell. The effect of a half-filled... 

Let us first consider the charge and spin distributions for atoms and ions of the first transition series (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn). The neutral ground-state TM electron configurations are of generic form s2d , except at n = 4 (Cr sM5) and n = 9 (Cu s d1") where the well-known anomalies associated with the special stability of half-filled and filled d shells are manifested. The simplest picture of ionic bonding therefore involves metal ionization from an s orbital to give the... 

East and co-workers have dealt with the electron spin relaxation problem for ions with half-filled shells (3c , S = 5/2, such as Mn(II) or Af, S = 7/2, such as Gd(III)) in the high-field limit 120). They allowed for a static ZFS, containing also terms with tensorial rank four and six, along with the rank-two term discussed before. The static ZFS was assumed to be modulated by rotational diffusion. In addition, they included the rank-two transient ZFS,... 

Figure 3 displays the molecular partition of the fragments for the three states previously discussed in the quantum mechanical section, at d= 6 k. Figure 3 A and 3 B respectively display the and 2 covalent states, and Figure 3 C shows the ionic 82 Charge Transfer state. It is worth examining the striking features of the molecular partitions in each case. In the A1 molecular partition, the disynaptic basin V(Cli, CI2), indicated by an arrow, corresponds to the Cl—Cl bond [22]. Two basins are found around Li, one corresponding to its core C(Li), and the second one, V(Li), to its valence odd electron (L shell). The 82 covalent state is characterized by two monosynaptic basins, Vi(Li) and V2(Li), located on both sides of the C(Li) basin in the molecular plane. They correspond to the half-filled 2p AO of Li. As when dealing with the previous state, the Cl atoms are bonded through a disynaptic basin, still noted V(Cli, CI2). In the ionic state, the Cl atoms are linked by a (3, -I) saddle point, or.

We now turn to the common valency of the lanthanides, viz. three. Here we find that depending on the number of / electrons in the ground state the first allowed transition may be either a c.t. transition or a 4f > 5d transition. The stability of the half-filled and completely-filled shells serves as a starting point to predict which of the two transitions is to be expected for a special case the c. t. transitions are at relatively low energy in the case of Eu3+(4/6) and Yb3+(4 f ), the 4f- -5d transitions are at relatively low energy in the case of Ce +(4/i), Pr +(4/2), Tb +(4/ ). Loh 18) has measured the lowest 4f- 5d transitions of all trivalent lanthanides in CaF2 (see Table 3). 

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