Helium fundamental properties

Let me try to rephrase the argument. We assume that the combination of a finite number of fundamental properties, via a combinatorial approach, leads to a discrete set of macroscopic physical possibilities. We also know empirically that the chemical elements occur in a discrete manner because there are no intermediate elements between, say, hydrogen and helium. The combinatorial approach can thus be taken as an explanation for the discreteness in the occurrence of elements and furthermore it justifies the fact that Mendeleev regarded the yet undiscovered elements like germanium as being physical possibilities rather than merely logical ones. 

It occurred to me that if one concentrated on this more fundamental sense of the concept of element, then the fact that helium does not seem to have properties in common with the alkaline earths would not be sufficient reason for not placing it among these elements in the periodic table. As I have later described this position, it was a form of why not argument rather than a positive reason for why helium should be placed among the alkaline earths. 

The true density of a solid is the average mass per unit volume, exclusive of all voids that are not a fundamental part of the molecular packing arrangement [55]. This density parameter is normally measured by helium pycnometiy, where the volume occupied by a known mass of powder is determined by measuring the volume of gas displaced by the powder. The true density of a solid is an intrinsic property characteristic of the analyte, and it is determined by the composition of the unit cell. 

In order to treat these observations and hypotheses in a theoretical framework as successfully as the case of electron localization in helium, we must first probe the dynamical properties of the IR absorptions in the subpicosecond regime. What perhaps is surprising and stimulating for future studies is the wealth of microscopic details that can be obtained on intermolecular interactions and electron transfer in liquids through picosecond spectroscopy, information of fundamental interest to chemical dynamics in the condensed phase. In this vein, we will conclude this chapter by an example of photoselective chemistiy in electron transfer processes that occur following laser excitation of e in the cluster. 

Let us consider the vdW interaction in helium in detail. Liquid helium is the only substance that does not solidify down to 0 K in the absence of external pressure. This is explained by the quantum character of the substance, whose zero point energy (ZPE) exceeds the crystal lattice energy [30]. At the same time, the macroscopic properties of helium (its crystal structure and thermochemical characteristics) do not differ fundamentally from those of other rare gases this allows to treat it in classical terms. Table 4.1 lists the structural and thermodynamic properties of rare gas molecules and crystals (see also [31]). 

The isotope helium-3 is difficult to isolate from the isotope helium-4. Interest in helium-3 is twofold First, its use in low-temperature refrigerators extends the minimum attainable temperature (outside of using magnetic cooling techniques) to about 0.3 K. Secondly, its properties are of fundamental interest in relation to theories of quantum statistical mechanics. 

Ernest Rutherford (1871-1937) identified two types of radiation from radioactive materials, alpha (a) and beta (j8). Alpha particles carry two fundamental units of positive charge and have essentially the same mass as helium atoms. In fact, alpha particles are identical to He ions. Beta particles are negatively charged particles produced by changes occurring within the nuclei of radioactive atoms and have the same properties as electrons. A third form of radiation, which is not affected by electric or magnetic fields, was discovered in 1900 by Paul Villard. This radiation, called gamma rays (y). 

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