Second-row atom

Functions with higher / values and with sizes like those of lower-/ valence orbitals are also used to introduce additional angular correlation by pemiitting angularly polarized orbital pairs to be fomied. Optunal polarization functions for first- and second-row atoms have been tabulated and are included in the PNNL Gaussian orbital web site data base [45]. 

Curtiss L A, K Raghavachari, P C Redfem, V Rassolov eind J A Pople 1998. Gaussian-3 (G3) Theory for Molecules Containing First and Second-row Atoms. Journal of Chemical Physics 109 7764-7776. 

McLean, A.D. Chandler, G.S. Contracted Gaussian basis sets for molecular calculations. I. Second row atoms, Z=ll-18 J. Chem. Phys. 72 5639-5648, 1980. 

Simple Basis Set for Molecular Wavefunctions Containing First- and Second-Row Atoms E. Clementi... 

The self-consistent field functions for the ground state of the first- and second-row atoms (from He to Ar) are computed with a basis set in... 

There is a second point to note in dementi s paper above where he speaks of 3d and 4f functions. These atomic orbitals play no part in the description of atomic electronic ground states for first- and second-row atoms, but on molecule formation the atomic electron density distorts and such polarization functions are needed to accurately describe the distortion. 

Three basis sets (minimal s-p, extended s-p and minimal s-p with d functions on the second row atoms) are used to calculate geometries and binding energies of 24 molecules containing second row atoms, d functions are found to be essential in the description of both properties for hypervalent molecules and to be important in the calculations of two-heavy-atom bond lengths even for molecules of normal valence. 

Some authors also recommended that the inner-shell octet of a second-row atom should be represented by four doubly occupied FSGOs arranged tetrahe-drally round the nucleus. 

The octet rule must be followed. That is, no second-row atom can be left with ten electrons (or four for hydrogen). If an electron pair moves to an atom that already has an octet (or two for hydrogen), another electron pair must simultaneously move from that atom to maintain the octet. When two electrons move from the C=C bond of ethylene to the hydrogen atom of for... 

Arising from studies of the photochemistry of benzenesulfonyl systems, extensive ab initio MO calculations have been made for various sulfonyl radicals and related species253. The STO-3G basis set, which includes d-type polarization functions on second-row atoms, was used. The inclusion of d orbitals on sulfur was found to be very... 

We have mentioned (p. 9) that, in general, atoms of the second row of the periodic table do not form stable double bonds of the type discussed in Chapter 1 (n bonds formed by overlap of parallel p orbitals). However, there is another type of double bond that is particularly common for the second-row atoms sulfur and phosphoms. For example, such a double bond is found in the compound H2SO3, as written on the left. Like an ordinary double bond, this double bond contains one s... 

Diamondoids, when in the solid state, melt at much higher temperatures than other hydrocarbon molecules with the same number of carbon atoms in their structures. Since they also possess low strain energy, they are more stable and stiff, resembling diamond in a broad sense. They contain dense, three-dimensional networks of covalent bonds, formed chiefly from first and second row atoms with a valence of three or more. Many of the diamondoids possess structures rich in tetrahedrally coordinated carbon. They are materials with superior strength-to-weight ratio. 

Fluorine is a second-row atom, so its atoms are much bigger than first-row hydrogen atoms. Thus, it makes sense that F atoms cannot get as close to one another as can H atoms. 

Barone, V., 1994, Inclusion of Hartree-Fock Exchange in Density Functional Methods. Hyperfine Structure of Second Row Atoms and Hydrides , J. Chem. Phys., 101, 6834. 

The role of d-type orbitals is not addressed in Table 1. This subject has been addressed for second-row atoms in previous reviews21,22 which contain many references to this subject. It is very difficult to define the energy and radius of the outer-sphere d-type orbitals (nd) in isolated atoms since they are not occupied in the ground state. Rather than make use of some excited state definition, we prefer to postpone a discussion of this subject until after an inspection of the calculated results on the molecular compounds. 

Ionization Potential (IP), Electron Affinity (EA), Maximal Charge Acceptance ANmax, and Electrophilicity Index Ground State for the First and Second Row Atoms (Units in eV)... 

A similar situation arises in the ir-v excited states of ethylene and acetylene where the n interactions become antibonding the excited states are consequently twisted (11) and bent (12) respectively. Another example is provided by triatomic molecules formed by second row atoms ifthe total number of valence electrons exceeds 16, the molecules are bent 33) since there are now antibonding electrons present and bending reduces the resulting unfavourable 7r interaction by replacing p AOs by hybrid AOs (cf. ozone, 13). 

The contribution to TAE of spin-orbit splitting in the constituent atoms is trivially obtained from a tabulation, while for molecules in degenerate ground states, CISD/MTsmall spin-orbit splittings are computed (allowing correlation from the 2s and 2p orbitals in second-row atoms). 

---