Physical chemistry Topic 1 Atoms, molecules and stoichiometry (original) (raw)

Semi-empirical Nuclear Mass Formula: Simultaneous Determination of 4 Coefficients

Asian Journal of Physical and Chemical Sciences, 2016

The deduction of 4 coefficients of the semi-empirical mass formula is presented as a function with two constants of proportionality: which relates the energy of the nuclear volume with volume and which relates volume with the mass number. Next the development of a proprietary method is presented-one that permits the simultaneous calculation of 4 of the 5 coefficients of the original semi-empirical formula. This method, which is direct and does not employ or require the use of successive approximations or iterations, is sufficiently didactic. It makes use of the experimental binding energies from 6 stable isotopes with a mass number odd-. Subsequently as validation, the coefficients are utilized for the theoretical calculation of the atomic masses of 237 stable isotopes and are compared with the experimental masses. Additionally, the calculation of the coefficients of proportionality and , the unit nuclear radius , the coefficients of nuclear surface tension , and the nuclear density are presented as well.

3 Isotopic Composition and Accurate Mass

In the context of general chemistry we rarely pay attention to the different isotopes of the individual elements involved in a reaction. For instance, the molecular mass of tribromomethane, CHBr3, is usually calculated as 252.73 g mol–1 on the basis of relative atomic mass from the Periodic Table. In mass spectrometry, however, we need to more accurately consider individual isotopes, because mass spectrometry is based upon the separation of ions by mass-to-charge ratio, m/z. [1-3]. Thus, there actually is no signal at m/z 252.73 in the mass spectrum of tribromomethane. Instead, major peaks occur at m/z 250, 252, 254, and 256 accompanied by some minor other ones. In order to successfully interpret a mass spectrum, one needs to understand iso-topic masses and their relation to the atomic weights, isotopic abundances, and the resulting isotopic patterns, and finally, high-resolution and accurate mass measurements. These issues are closely related to each other, offer a wealth of analytical information, and are valid for any type of mass spectrometer and any ionization method employed.

Mesures directes de masses et évaluation globale des masses atomiques

2018

The Atomic Mass Evaluation (AME), started in the 1960s, is the most reliable source for comprehensive information related to atomic masses. It provides the best values for the atomic masses and their associated uncertainties by evaluating experimental data from decay, reactions, and mass spectrometry. In this thesis, the philosophy and the most important features of the Ame will be discussed in detail. The most recent developments of the latest mass table (AME2016), such as molecular binding energy, energy correction of the implantation measurements, and the relativistic formula for the alpha-decay process, will be presented. Another part of this thesis concerns the data analysis from the Penning-trap spectrometer ISOLTRAP at ISOLDE/CERN. The new results are included in the global adjustment and their influences on the existing masses are discussed. The last part of this thesis is related to the systematic error studies of the ISOLTRAP multi-reflection time-of-flight mass spectromet...

Determination of the Atomic Mass Constant by Ion Accumulation

An experiment for the direct measurement of the atomic mass constant was performed by accumulating ions from an ion beam up to a weighable mass. The aim of this experiment was to develop an alternative approach for the redefinition of the SI unit kilogram. In a recent experiment a mass of about 300 mg bismuth was accumulated and the atomic mass unit could be determined with a relative uncertainty better than 1.0×10 -4 .

Coefficients of different macro-microscopic mass formulae from the AME2012 atomic mass evaluation

Nucl. Phys. A 917 1, 2013

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On the Mass Number A Dependence of the Semi-empirical Mass Formula

Journal of the Korean Physical Society, 2010

The semi-empirical mass formula was tested against possible variations in the mass number dependence of each of ¯ve terms in the formula for nuclei far from the stability line in the chart of nuclides. The exponent of A in each term of the mass formula was treated as a new free parameter, and both the energy coe±cients and the exponents were determined using the least-squares-¯tting technique. The ¯tting procedure was performed separately for the three groups of nuclides that had been divided based on the order of their stability. Except for the pairing energy term, the mass number, A, ependence of the semi-empirical mass formula was not altered, within 1%, for any of the three groups of nuclides.