Neon core

Note. The electronic configuratioa of any element can easily be obtained from the periodic table by adding up the numbers of electrons in the various quantum levels. We can express these in several ways, for example electronic configuration of nickel can be written as ls 2s 2p 3s 3d 4s. or more briefly ( neon core ) 3d 4s, or even more simply as 2. 8. 14. 2... 

All the third-row elements have a neon core containing ten electrons The ele-... 

In other words, the significant separation is not between ligands and central ion electrons but between the electronic density of the completely occupied lower M.O. and the partly filled shell containing an integral number of electrons. This separation is of the same nature as that between the neon core and the one valency electron in the neutral sodium atom or the two valency electrons in the isolated magnesium atom. It is worth remarking that this separation has no direct group theoretical certainty. It is true that the orbital symmetry types l or yD are deter-... 

The Group 12 elements differ markedly from those in Group 2 in nearly all respects except having II as their only important oxidation state. Thus, while the Zn2+ and Mg2+ ions are very similar in their 6-coordinate radii (0.88 A and 0.86 A, respectively), Zn2+ has a relatively polarizable 3d10 shell whereas the neon core of Mg2+ is very hard. This special combination of softness and a high charge-to-radius ratio appears to be responsible for the unique role played by zinc in biochemistry (see Section 15-17). 

Sulfur has six electrons beyond the neon core the first two of these are in the 3s orbital, and the next four are in the 3p orbitals. The ground-state configuration of sulfur is [Ne]3s 3p. When four electrons are put into three p orbitals, two electrons must occupy one of the orbitals, and the other two occupy different orbitals to reduce electron-electron repulsion. According to Hund s rules, the electrons spins are parallel, and the sulfur atom is paramagnetic. 

Consider the case of sodium metal. Of the 11 electrons, the 10 forming the neon core are localized around each Na nucleus, leaving one per atom to fill the MOs that pervade the crystal. If there were N atoms in the crystal N MOs could be formed by use of one 3s orbital from each. Although these MOs have varying amounts of bonding and nonbonding character, their energies form a continuum within the 3s band. 

The symbol [He] is called the helium core and represents [Ne] is called die neon core and represents [Ar] is called the argon core and represents... 

The 3s and 3p orbitals are filled in going across the third period of the periodic table from sodium through argon. Atoms of these elements, like all atoms beyond neon, have their 10 innermost electrons in the neon electron configuration of ls 2s 2p. Therefore, these atoms have a neon core, which may be designated Ne ... 

What is the core of an atom Specifically, what is the neon core ... 

In an alkali metal atom such as sodium, the 3s electron penetrates the neon core, i.e., it moves into the field of attraction of the nucleus, being only partially screened by the K and L shells. In an excited sodium atom the electron in a 3p orbital penetrates the electron cloud to a lesser extent, and the electron raised to a 3d orbital is practically non-penetrating. Thus the 3s, 3p, and 3d orbital in a many-electron atom have different energies whereas these orbitals in hydrogen atom have the same energy. 

The sublevels having lower energies than 3p can be read across the periods Ifom left to right in the periodic table, as in Figure 11.15 Is 2s 2p 3s 3p If the neon core were to be used, these would be represented by [Ne]3s 3p ... 

Argon core, neon core Election configuration... 

The advantages of using pseudopotentials are dramatically illustrated by DQMC calculations for the Fe atom carried out by Mitas for all electrons, for a neon core pseudopotential, and for an argon core pseudopotential the relative computational effort for a fixed statistical uncertainty was in the order 6250, 60, and 1, respectively. Thus, the appeal of pseudopotentials is strong. Of course, the additional (systematic) uncertainty introduced with the use of pseudopotentials is a disadvantage. Additional work will undoubtedly resolve the relative advantages and disadvantages. 

The sodium atom has an outer 3s electron and a neon core. Since the 3s electron is the outermost electron, and since it is shielded from the nuclear charge by the core electrons, it contributes greatly to the size of the sodium atom. The sodium cation, having lost the outermost 35 electron, has only the neon core and carries a charge of 1+. Without the 35 electron, the sodium cation (ionic radius = 95 pm) becomes much smaller than the sodium atom (covalent radius = 186 pm). The trend is the same with all cations and their atoms, as shown in Figure 8.12 t. 

However, for the case of the effective nuclear charge Zeff for the excited outer electron in the sodium flame test, we found a noninteger value due to incomplete screening of the nuclear charge by the shell of electrons between the (n = 3, n = 4) shells of the atom and what we can call the Neon-core of the inner part of the Na atom. In the case of the L energy, the transition is from the (n = 3) —> (n = 2) level, so the K shell is between the L shell and the bare nucleus for sure. Further, the L shell may still be mostly occupied with perhaps one vacancy so the Ne core may be mostly intact. 

---