Noble-gas like

Of course, commercially available transition metal complexes are stable at room temperature because they have achieved an 18-electron noble gas-like electronic configuration. Thus, molecules like iron pentacarbonyl [Fe(CO)s], ferrocene [Fe(C5H5)2], as well as piano-stool complexes such as C5H5Co(CO)2 are chemically quite inert. In order to study bimolecular reactions, it is necessary to first prepare unsaturated complexes. For studies using molecular beams, one approach is through photolysis of a stable volatile precursor in a supersonic nozzle. 

Depending on the type of interaction between an adsorbed particle and a solid state surface there are cases, where adsorption enthalpies can be calculated using empirical and semi-empirical relations. In the case of atoms with a noble-gas like ground-state configuration and of symmetrical molecules the binding energy (EB) to a solid surface can be calculated as a function of the polarizability (a), the ionization potential (IP), the distance (R) between the adsorbed atom or molecule and the surface, and the relative dielectric constants (e) (Method 9) [58-61] ... 

If the elements 112 and 114 have a noble-gas like character [62], then, in a fictitious solid state, they would form non conducting colorless crystals. A physisorptive type of adsorption may occur and their adsorption properties, for example on quartz, can be calculated with this method [61], see Table 3. For physisorbed noble gas atoms a roughly uniform distance to different surfaces of about 2.47 0.2 A was deduced from experimental results [63]. 

The Madelung constant is unique for each crystal stmcture and is defined only for those whose interatomic vectors are fixed by symmetry. The Born exponent, n, can be estimated for alkali halides by the noble-gas-like electron configuration of the ion. It can also be estimated from the compressibility of the crystal system. For NaCl, n equals 9.1. 

A consideration of the previous statements leads one to expect a relatively simple substitution chemistry for the alkali ions in solution. Due to their noble gas like electron configuration, the substitution rates should show a straightforward relationship to physical properties such as charge and size. However, it is naive to assume that complex formation involving main group metal ions is an easily resolved problem. There exist several non-trivial facts, which cannot readily be explained. It is a close examination of these, which will provide some interesting insight into the mechanism of metal complex formation of alkali ions. 

Over many years alkali ions in solution almost escaped the attention of the chemists. The alkali metals belong to a group of elements which in their common state of ionization possess a closed electronic shell and hence should show a noble-gas-like chemistry. Being charged particles and differing in size the various members of this series of course show individual characteristic interactions with other charged, di- or multi-polar ligands, well understood in terms of classical theory. 

The numerical value of n can be derived from measurements of the compressibility of the solid and may also be estimated theoretically. The experimentally derived values and the values calculated by Pauling for noble gas-like ions are given in Table 2-4. It can be seen that the experimental... 

A more recent fully relativistic treatment of the interaction of Cn with metallic surfaces such as Au or Pd, predicts weaker absorption of Cn than Hg on these metals (Pershina et al. 2004) however, due to metal-metal interaction, Cn was predicted to sorb at much higher temperatures than Rn, which sorbs only by van der Waals forces. The capability of Cn to form metallic bonds was also predicted by Eichler and Rossbach (1983). On the other hand, on chemically inert surfaces such as quartz or ice, mercury is found to be adsorbed only at very low temperatures (—100°C) (Sovernaet al. 2005) to — 160°C (Yakushevet al. 2001,2003). Thus, the latter surfaces are much less suitable to distinguish between a volatile metal and a noble gas-like behavior of Cn, than sorption on, for example, a Au surface. Recent developments in the four-component Density Functional Theory, that is, the spin-polarized (SP) 4c-DFTallow to make very accurate predictions on the adsorption enthalpy of Cn on a Au surface, which is 20 kj/mol weaker than that for Hg (Pershina et al. 2009). 

Each period ends with an element known as a noble gas. Like kings and queens set apart in impenetrable castles, these gases are chemically unreactive and composed of individual atoms. 

The Geiger counter, invented in 1928 and named after one of its two inventors, H. Geiger and E.W. MuUer, counts particles emitted by radioactive nuclei in a non-reactive noble gas, like argon. Alpha and beta particles are detected this way. 

Physisorption of Noble Gases and Noble-Gas Like Elements... 

Another approach to assess volatility data for noble gas like elements is based on the fundamental law of corresponding states, which was established by van der Waals in 1880. It suggests the existence of a universal equation of states (59) valid for various liquids and gases with high similarity of bonding, interaction, and structure. In the case of the heavier noble gases these requirements are indeed fulfilled. The variables in this equation are the parameters of state reduced by the critical values. 

However, using the data for the heavy noble gases (Ar-Rn) a complete set of critical data is deduced, which is used as follows to describe the volatilization process of the noble gas element 118 and of the potentially noble-gas like elements Cn and FI. The reduced vapor pressure equation is given as ... 

Under the assmnption that elements Cn, FI, and 118 behave as typical heavy noble gases [54] and imdergo pure van der Waals interaction with metal smfaces, the adhesion model based on an approach given in [80] can be applied. The adsorption enthalpy of noble-gas like elements was related to the adhesion of atoms to a smface with a certain surface energy. This approach revealed that the adsorption enthalpy of a noble gas ( ) on a metal surface is linearly correlated to the adsorption enthalpy of Xe on the same metal. 

Table 5 Proportionality factors C(E) connecting the adsorption enthalpy of noble-gas like elements on metals with the adsorption enthalpy of Xe on these metals...

C(E) for noble gases Ne-Xe from [78] and empirically deduced for He and Rn and for assumed noble-gas like elements Cn and FI using atomic data from [56-58, 73]... 

---