Cobalt atomic weight

The atomic weight increases regularly across the row except for the inversion at cobalt and nickel. We would expect the atomic weight of Ni to be higher than that of Co because there are more protons (28) in the Ni nucleus than in the Co nucleus (27). The reason for the inversion lies in the distribution of naturally occurring isotopes. Natural cobalt consists entirely of the isotope 2 Co natural nickel consists primarily of the isotopes Ni and Ni, the 58-isotope being about three times as abundant as the 60-isotope. 

Wurtz s point about cobalt and nickel is well taken given that classification was by atomic weight there would have been no basis for the prediction of two elements between iron and copper, had neither cobalt or nickel been known, and no basis for predicting the existence of the other had only one of them been known. 

The atomic number, which appears above each element symbol, represents the meaningful order in the periodic table. When an element is referred to by an integer, this number means the atomic number, not the atomic weight. Thus, element 27 is cobalt (whose atomic number is 27), not aluminum (whose atomic weight is 27). In Chapters 2 and 3, these two concepts are more carefully defined for now, simply bear in mind the distinction between atomic number and atomic weight. 

Symbol Ni atomic number 28 atomic weight 58.693 a transition metal element in the first triad of Group VIll(Group 10) after iron and cobalt electron configuration [Ar]3d 4s2 valence states 0, -i-l, +2, and -f-3 most common oxidation state +2 the standard electrode potential, NF+ -1- 2e Ni -0.237 V atomic radius 1.24A ionic radius (NF+) 0.70A five natural isotopes Ni-58 (68.08%), Ni-60 (26.22%), Ni-61 (1.14%), Ni-62 (3.63%), Ni-64 (0.93%) nineteen radioactive isotopes are known in the mass range 51-57, 59, 63, 65-74 the longest-lived radioisotope Ni-59 has a half-life 7.6x10 years. 

An attempt to clear up the constitution of these salts was then made, and Jorgensen,1 with the help of molecular-weight determination, proved that the substances contained only one cobalt atom in the molecule. The formula were then halved and written as ... 

For use of the complex in preparing cobalt chloride for determining atomic weights, see references 4 and 5. 

This brings the three elements into complete harmony with the general scheme. It is always possible that further research may ultimately prove, in a similar manner, that nickel and cobalt are not real, but only apparent, exceptions to the Periodic Law. It must be admitted, however, that this is very unlikely, since it necessitates either very considerable errors in the modem determinations of their atomic weights, or the assumption that one or both of these elements is in reality complex. 

The most recent views on the Periodic Classification suggest an entirely different method of removing the anomaly, namely, that the atomic weight is not the correct property to use in arranging the elements rather should one be chosen which increases by a constant amount in passing from one element to the next. Physical theory indicates the positive nuclear charge of the atom to be one such property, whilst experimentally it is found that the X-ray spectra afford such a property, and eliminate the nickel-cobalt anomaly.1... 

Moissan 3 in 1880 called attention to the fact that the affinities of chromium, manganese, iron, cobalt, and nickel for oxygen and the heats of formation of oxides, chlorides, bromides, iodides, and sulphides decrease as the atomic weights rise. 

Atomic Weight.—Approximate Atomic Weight.—That the atomic weight of cobalt is approximately 59 and not a multiple or submultiple of this amount is evident from a variety of considerations, namely ... 

The specific heat of cobalt is 0-108. Assuming a mean atomic heat of 6-4, the atomic weight, according to Dulong and Petit s Law, is approximately 59-8. 

The most appropriate position for cobalt in the Periodic Table is, as explained in the opening chapter of this volume, between iron and nickel. Assuming the atomic weights of iron and nickel to be correct, we should expect the value for cobalt to be greater than 55-84 (at. wt. of iron), but less than 58-68 (at. wt. of nickel). 

Analyses of these compounds indicate that the atomic weight of cobalt is 59-0. 

The following year Marignac6 made a number of preliminary experiments on the atomic weight of cobalt. Li two experiments anhydrous cobalt sulphate was calcined to oxide ... 

The foregoing results are of little or no value in comparison with those that have been subsequently obtained. They vary very considerably, but undoubtedly point to a value round about 59 for the atomic weight of cobalt. The results obtained by Schneider, Som-maruga, and Winkler are much higher than all the others, and it will be noticed that in the hands of Lee, Sommaruga s method gave a much lower value. 

In 1897-1899, the work of Richards and Baxter4 on the atomic weight of cobalt was published. Anhydrous cobaltous bromide was prepared by direct union of the pure elements and the product sublimed in a stream of hydrogen bromide and nitrogen. The bromine in the salt was determined by the two usual methods, the amount of silver required to precipitate it being first measured and then the precipitated silver bromide being collected and weighed. The final results were as follow ... 

The most appropriate position for nickel in the Periodic Table is, as explained in Chapter I, the end of the first horizontal series of triads in Group VIII. An atomic weight greater than that of cobalt, namely, 58-97, but less than that of copper, namely, 63-57, is thus to be expected. 

Cobalt, in its properties, is an excellent intermediary between iron and nickel, and, moreover, it is clearly a suitable element to constitute the first of the central vertical triads of Group VIII, namely, Co, Eh, and Ir. Hence, if the Periodic Law holds absolutely, the atomic weight of cobalt should exceed that of iron, but not that of nickel. Either, therefore, the atomic weight of cobalt is slightly too high or that of nickel is slightly too low. 

According to the Periodic Classification, rhodium, which in its properties forms a mean between cobalt and iridium, and betw een ruthenium and palladium, should have an atomic weight intermediate between the values for these extreme elements, namely, from 102 to 105. 

The Grouping of Elements into Triads—Atomic Weights of the Elements— General Properties of tho Elements—Comparative Study of Iron, Cobalt, and Nickel—Their Position in tho Periodic Table—Comparative Study of Iron, Ruthenium, and Osmium—Comparative Study of Cobalt, Rhodium, and Iridium—Comparative Study of Nickel, Palladium, and Platinum. 

Occurrence of Cobalt—History—Preparation—Pyrophoric Cobalt—Physioal Properties—Ooelusion of Hydrogen—Chomioal Properties—Atomic-Weight —Uses -Electro-deposition—Alloys. 

In addition to its many uses in medical and physiological research, radioisotopes are used in therapy, and in agricultural and industrial research. Radioactive cobalt, for example, became available for the treatment of deep-seated cancer. This isotope of atomic weight 60 loses half its radioactivity in about five days and is more than 300 times as powerful as radium. It is taking the place of radium and X-ray therapy in many hospitals. 

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