Atomic weight approximate

Every element has an atomic weight approximately (but not exactly) equal to the total number of protons and neutrons that are present in each of its atoms. The atomic weights are not exactly equal to this sum because, in addition to other reasons, not all atoms of a particular element have the same number of neutrons. Most elements have one or more isotopes, which means atoms with the same number of protons but different numbers of neutrons. For example, the element nitrogen has two natural isotopes, 14N which has 7 protons and 7 neutrons, and 15N which has 7... 

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 ... 

Atomic Weight.—Approximate Atomic Weight—-That the atomic weight of rhodium is approximately 103 and not a multiple or fraction... 

Atomic Weight.—Approximate Atomic Weight.—That the atomic... 

Atomic Weight.—Approximate Atomic Weight.—Several considerations lead us to the conclusion that the atomic weight of osmium is of the order of 191. The chief reasons may be summarised as follows ... 

If the region between helium and uranium contains 91 elements then five are as yet undiscovered. These have been predicted and named (1) eka-manganese with an atomic number 43 and an atomic weight approximately 100 (2) dwi-manganese, atomic number 75 falling between tungsten and osmium (3) eka-iodine, atomic number 85 (4) eka-neodym-ium, a rare earth element of atomic number 61 and (5) eka-caesium of atomic number 87. Of these, greatest interest has... 

Atomic weight Approximately the sum of the number of protons and neutrons found in the nucleus of an atom. This sum is also called mass number. The atomic weight of oxygen, for example, is approximately 16, with most oxygen atoms containing 8 neutrons plus 8 protons. The atomic weight of aluminum is 27 it contains 14 neutrons and 13 protons. 

Dulong and Pedt s law The product of the atomic weight and the specific heat of a metal is constant of value approximately 6-2. Although not true for all metals at ordinary temperatures, these metals and several non-metals approximate to the law at high temperatures. 

Each of the elements has a number of isotopes (2,4), all radioactive and some of which can be obtained in isotopicaHy pure form. More than 200 in number and mosdy synthetic in origin, they are produced by neutron or charged-particle induced transmutations (2,4). The known radioactive isotopes are distributed among the 15 elements approximately as follows actinium and thorium, 25 each protactinium, 20 uranium, neptunium, plutonium, americium, curium, californium, einsteinium, and fermium, 15 each herkelium, mendelevium, nobehum, and lawrencium, 10 each. There is frequently a need for values to be assigned for the atomic weights of the actinide elements. Any precise experimental work would require a value for the isotope or isotopic mixture being used, but where there is a purely formal demand for atomic weights, mass numbers that are chosen on the basis of half-life and availabiUty have customarily been used. A Hst of these is provided in Table 1. 

While chemists differed on the relative importance of prediction and accommodation, it seems fair to approximate the consensus as follows. The reasons for accepting the periodic law are, in order of importance, [1] it accurately describes the correlation between physicochemical properties and atomic weights of nearly all known elements ... 

Perhaps the earliest hints of any numerical regularity among the atomic weights of the elements was discovered as early as 1817 by Dobereiner. He was the first to notice the existence of various groups of three elements, subsequently called triads, that showed chemical similarities. In addition, such elements displayed an important numerical relationship, namely that the equivalent weight, or atomic weight, of the middle element is the approximate mean of the values of the two flanking elements in the triad. 

Moreover, if we consider atomic numbers instead of atomic weights for the triads discovered in Ihe 19th century, it turns out that the atomic number of Ihe middle element is exactly the average vt the other two elements Indeed, about halt of al Ihe possible triads in the modern periodic table are exact in this sense However many other potential triads are not even approximately correct in that the atomic number of the middle dement is nowhere near Ihe average of Ihe other two... 

The law of Dulong and Petit states that the molar heat capacity of crystalline elements is approximately 25 J/mol deg. With this law, we can calculate approximate atomic weights from heat capacity data. 

EXAMPLE 18.14. An element has a specific heat of 0.123 J/g deg. Calculate its approximate atomic weight. 

The molar heat capacity is about 25J/moldeg, and the specific heat is 0.123 J/g deg. Therefore, the atomic weight is approximately... 

The specific heat of a certain element is 0.119J/g deg. Using the law of Dulong and Petit, calculate its approximate atomic weight. 

Calculate the approximate atomic weight of lead using its specific heat, 0.12 J/g deg, and the law of Dulong and Petit. 

Cover design by Nick Krenitsky is representational only and is not intended to reflect a scientifically accurate model of the periodic chart of the elements in the cover design, boldface type at top of square is atomic number, followed by chemical symbol and approximate atomic weight. 

When 3.00 grams of a certain metal are completely oxidized, 3.80 grams of its oxide are produced. The specific heat of the metal is 0.052 cal/g °C. What is the approximate atomic weight of this metal ... 

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