Neon, atomic weights

Aston began the examination of those elements whose atomic weights were not integers. He worked first with neon. By 1919, definite proof of the physical separation of the two isotopes of the gas neon was established. He had found neon to be a mixture of 90% of neon with atomic weight of 20, and 10% neon, atomic weight 22—hence its accepted fractional weight of 20.2. Here was the first conclusive proof of the existence of isotopes, and the explanation of fractional atomic weights. 

Thus, the three isotopes of neon, atomic weights 19.99, 20.99, and 21.99, have the same atomic number (10) but different mass numbers. All the nuclei of neon have 10 protons, but the nuclei of the isotope of mass number 20 have 10 neutrons, those of mass number 21 have 11 neutrons, and those of mass number 22 have 12 neutrons. Symbolically, these nuclei are represented as fJNe, iJNe, wNe. The mass number is the nearest integer to the atomic weight of the isotope. 

Neon (atomic weight 20.183) has three stable isotopes of mass numbers 20, 21, and 22, which occur in a relative abundance in atmospheric air in the ratios 10,000 28 971. Five other unstable isotopes are known. 

Table 4.2 Weights of excited configurations for the Neon atom...

In 1913, J. J. Thomson4 demonstrated that neon consists of different atomic species (isotopes) having atomic weights of 20 and 22 g/mole. Thomson is considered to be the father of mass spectrometry. His work rests on Goldstein s (1886) discovery of positively charged entities and Wein s (1898) demonstration that positively charged ions can be deflected by electrical and magnetic fields. 

Sir William Ramsay, 1852-1916. Scottish chemist and physicist who, with Lord Rayleigh and M. W. Travers, discovered the inert gases helium, neon, argon, krypton, and xenon. He also made a remarkable determination of the atomic weight of radon (radium emanation), the heaviest of the inert gases. 

The diffusion method depends on the fact that the velocity of a molecule is inversely proportional to the square root of its molecular weight. Slight separations were made years ago in the case of hydrochloric acid and of mercury but the results were disappointing on account of the very small yields. The isotopes of neon with atomic weights of 20 and 22 have been separated rather successfully by diffusion. Hydrogen and deuterium also have been separated by diffusion. 

Was this all just a fabrication Or was it a clue to the interpretation of the fractional weights of chlorine, lead and neon Perhaps chlorine, which chemists knew as a simple element, was in reality, a mixture of isotopes, each of which possessed atomic weights of whole numbers. When mixed in less than identical amounts, these isotopes would yield a gas with an average atomic weight of 85.46. Was this the answer to the inconsistencies of Prout s Theory Was the death knell of another dogma of chemistry to be heard ... 

Theory shows that the vapour pressures of ortho- and para- states of diatomic molecules ( 23.IV) should be diflferent, and this has been confirmed experimentally for hydrogen.3 According to Herzfeld and Teller, the heavier isotope may have a lower or higher vapour pressure than the lighter one. For neon isotopes, the vapour pressure is a linear function of the atomic weight. ... 

By measuring the deflection of the beams, relative values of ne/M for different ions can be determined. Since e is constant, relative values of ne/M for different ions are also inverse relative values of M/n therefore this method permits the direct experimental determination of the relative masses of atoms, and hence of their atomic weights. By this method Thomson discovered the first known non-radioactive isotopes, those of neon, in 1913. 

The proper location of radon in the periodic table was determined by Scottish chemist Sir William Ramsay (1852-1916). Ramsay was also involved in the discovery of three other noble gases neon, krypton, and xenon. In 1903, Ramsay was able to determine the atomic weight of radon. He showed that it belonged beneath xenon in Group 18 (VIIIA) of the periodic table. 

Using his positive ray analysis,. 1.. 1. Thomson hits shown that atmospheric neon contains two isntojtes, one with an atomic weight 20 and the other 22. This conclusion has Item confirmed by Aston, a who obtained evidence of two isotojs H of atomic weights 20 and 22 in proportion ) to 1. This accounts for the accepted value of 20.2, There is also some evidence of a third isotope of value 21, comprising about 1 kt cent of the whole. If this conclusion is confirmed this would furnish mi interesting triad somewhat similar to those found in (Jroup VIII. 

Physical and Chemical Properties Sodium is an alkali metal which readily loses one electron hence, + 1 is its only oxidation state. The atomic number of sodium in the Periodic Table of the elements is 11 (Group 1), and its atomic weight is 22.98977. Sodium melts at 97.8°C and boils at 881.4 °C. The sodium atom in its ground state has the electron configuration 1 s, 2 s p , 3 s which corresponds to a case with an electronic nature of the inert gas neon, and an additional single-valence electron in the 3 s orbital. The configuration occurs only in the oxidation state I" in ionic compounds. Most of the ionic compounds are soluble in water and highly ionized. 

Problem 2.10. Neon has three naturally occurring isotopes of mass number (to the closest atomic mass unit) of 20.0, 21.0, and 22.0. Their abundances (percent of those found in nature) are 90.92 percent, 0.257 percent, and 8.82 percent. What is the atomic weight of neon ... 

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