Helium physical properties

Fourteen isotopes are now recognized. 258Md has a half-life of 2 months. This isotope has been produced by the bombardment of an isotope of einsteinium with ions of helium. Eventually enough 258Md should be made to determine its physical properties. 

Pure Elements. AH of the hehum-group elements are colorless, odorless, and tasteless gases at ambient temperature and atmospheric pressure. Chemically, they are nearly inert. A few stable chemical compounds are formed by radon, xenon, and krypton, but none has been reported for neon and belium (see Helium GROUP, compounds). The hehum-group elements are monoatomic and are considered to have perfect spherical symmetry. Because of the theoretical interest generated by this atomic simplicity, the physical properties of ah. the hehum-group elements except radon have been weU studied. 

Table 3. Physical Properties of the Helium-Group Elements...

Thermal conductivity detector. The most important of the bulk physical property detectors is the thermal conductivity detector (TCD) which is a universal, non-destructive, concentration-sensitive detector. The TCD was one of the earliest routine detectors and thermal conductivity cells or katharometers are still widely used in gas chromatography. These detectors employ a heated metal filament or a thermistor (a semiconductor of fused metal oxides) to sense changes in the thermal conductivity of the carrier gas stream. Helium and hydrogen are the best carrier gases to use in conjunction with this type of detector since their thermal conductivities are much higher than any other gases on safety grounds helium is preferred because of its inertness. 

We shall now describe the main physical properties of helium ... 

Neon—helium continuous lasers, 17 372 Neonicotinoid insecticides, 14 346 Neopentanal trifluoroborane, 4 144t Neopentanoic acid, 5 60-65 physical properties, 5 60t production from butylenes, 4 427 Neopentyl glycol, 12 670-672... 

The nuclear chemists at the Lawrence Berkeley Laboratory worked with extremely small samples of lawrencium with short half-lives, which made it difficult to determine the new elements chemical and physical properties. Most of its isotopes spontaneously fission as they give off alpha particles (helium nuclei). Lawrencium s melting point is about 1,627°C, but its boiling point and density are unknown. 

Elemental composition Cl 54.16%, N 21.40%, O 24.44%. The compound can be identified by its color and other physical properties. Analysis may be done by GC/MS using a diluent gas such as helium. Alternatively, it may be added to an olefinic double bond and the derivatives identified by physical properties, IR, and mass spectra. (See Reactions.)... 

Elemental composition Os 74.82%, 0 25.18%. The compound can be identified by its physical properties, such as, odor, color, density, melting-, and boiling points. Its acrid odor is perceptible at concentrations of 0.02 mg/hter in air. The oxide also produces an orange color when a small amount of the compound or its aqueous solution is mixed with an aqueous solution of ammonia in KOH (see Reactions). Aqueous solution of the tetroxide may be analyzed for osmium by AA or ICP spectrometry (see Osmium). Vapors of the tetroxide may be purged from an aqueous solution by helium, adsorbed over a trap, and desorbed thermally by helium onto a GC. Alternatively, a benzene or carbon tetrachloride solution may be injected onto the GC and the compound peak identified by mass spectrometry. The characteristic mass ions for its identification should be 190 and 254. 

Homogeneous Liquids. The physical properties important in determining the suitability of a liquid for propellant application are the freezing point, vapor pressure, density, and viscosity. To a lesser extent, other physical properties are important such as the critical temperature and pressure, thermal conductivity, ability to dissolve nitrogen or helium (since gas pressurization is frequently used to expel propellants) and electrical conductivity. Also required are certain thermodynamic properties such as the heat of formation and the heat capacity of the material. The heat of formation is required for performing theoretical calculations on the candidate, and the heat capacity is desired for calculations related to regenerative cooling needs. 

Unlike solids and liquids, different gases show remarkably similar physical behavior regardless of their chemical makeup. Helium and fluorine, for example, are vastly different in their chemical properties yet are almost identical in much of their physical behavior. Numerous observations made in the late 1600s showed that the physical properties of any gas can be defined by four variables pressure (P), temperature (T), volume (V), and amount, or number of moles in). The specific relationships among these four variables are called the gas laws, and a gas whose behavior follows the laws exactly is called an ideal gas. 

Physical properties Density Specific gravity Pore structure True density as measured by helium displacement Apparent density Specification of the porosity or ultrafine structure of coals and nature of pore structure between macro, micro, and transitional pores... 

Of the predominantly nonmetallic elements, seven are solids under ordinary atmospheric conditions (B, C, Si, P, S, Se, and I), only one is a liquid (Br), and the remainder are gases (H, N, 0, F, Cl, He, Ne, A, Kr, and Xe). The physical properties of these elements present far more striking contrasts than do those of the metals. Thus, among the nonmetals one encounters the extremely volatile helium, which boils at -267°C (i.e., just 5°C above absolute zero), and the nonvolatile element carbon, which melts at about 3500°C. Similarly, the densities and other physical properties of these elements differ tremendously, as is made more evident by an inspection of a table of physical properties of the elements. 

Because of its small size (collision diameter 0.20 nm), helium would appear to be a useful probe molecule for the study of uitramicroporous carbons. The experimental difficulty of working at liquid helium temperature (4.2 K) is the main reason why helium has not been widely used for the characterization of porous adsorbents. In addition, since helium has some unusual physical properties, it is to be expected that its adsorptive behaviour will be abnormal and dependent on quantum effects. 

The closed-shell electronic structures of the noble gas atoms are extremely stable, as shown by the high ionization enthalpies, especially of the lighter members (Table 14-1). The elements are all low-boiling gases whose physical properties vary systematically with atomic number. The boiling point of helium is the lowest of any known substance. The boiling points and heats of vaporization increase monotonically with increasing atomic number. 

Other Thermometric Devices. The vapor pressure of a pure liquid or solid is a physical property sensitive to temperature and thus suitable for use as a thermometer. The use of a liquid-nitrogen vapor-pressure thermometer is suggested for the range 64 to 78 K in Exp. 47. At very low temperatures (1 to 4.2 K), the vapor pressure of liquid helium can be used. 

We are now in a position to discuss the physical properties of surface state electrons. We choose liquid helium for the dielectric. According to H. L. Anderson (1989) the dielectric constant for liquid helium is given by... 

Kamerlingh Onnes had only a thimbleful of helium liquid, but it was to be the grand overture to his explorations in a vast new temperature region, a place of intense cold where the physical properties of many substances changed remarkably. Even at the temperature of liquid air, one could perform strange tricks. One can, for example, mold... 

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