ATOMIC WEIGHTS 



405 



ATRIUM 



ATOMIC WEIGHTS. The atoms of any 

 chemical element have a different weight from 

 those of any other element. It is, of course, 

 impossible to weigh atoms individually. A 

 number of different kinds of physical experi- 

 ments, however some with radioactive ele- 

 ments, some with electricity and some with the 

 microscope lead consistently to the conclusion 

 that the smallest atoms, those of hydrogen, 

 weigh 16.6X10 25 grams each. In other words, 

 it would take 6 million million million million 

 hydrogen atoms to weigh a gram (1/454 of a 

 pound). When a chemist speaks of atomic 

 weights, however, he means only the relative 

 Jits of the atoms; that is, how many times 

 heavier one kind of atom is than another. 

 He infers these relative weights from his as- 

 sumption that every chemical action conducted 

 on a sufficiently large scale to enable him to 

 weigh the reagents and their products is really 

 made up of millions of little reactions among 

 the individual atoms. 



For example, he finds that one gram of 

 hydrogen combines with 7.94 grams of oxygen. 

 From this he infers that an atom of oxygen 

 must weigh 7.94 times as much as an atom 

 of hydrogen, or twice 7.94 times as much, or 

 times 7.94 times as much, or some other 

 whole number of times 7.94 times as much. 

 There are various ways of deciding which of 

 these possibilities is correct. (For these see 

 books on chemistry.) In this instance twice 

 7.94=15.88 is chosen. If, then, the weight of a 

 hydrogen atom (the highest of all atoms) be 

 i as the unit, the atomic weight of oxygen 

 is 15.88. A majority of modern chemists, how- 

 ever, prefer to make oxygen the basis of the 

 system of atomic weights, rather than hydro- 

 They take exactly 16 as the atomic 

 weight of This makes that of hydro- 



1.008 instead of exactly 1. In the table 

 elements given i; the 



atomic weights are upon this basis. Except 

 hydrogen, helium is the of lowest 



.-lit, 4.0. Uranium has t atomic 



weight, 238.5; thorium the D st, 232.4; 



in the next, 226. See ATOM; ATOMIC 

 THEORY. 



ATONEMENT, a toltn' m,-nt, the 

 making n.< n< . or reconciling those who 1 

 been separated because of acts of offense or 

 strong differences of opinion. Atonement means 



M ihation. This act may consist of 

 offering, such as a present, or an apology, or a 

 I'l. i for f or ui vcness. 



While this \\ord is sometimes used in con- 

 30 



nection with the relations of men in every-day 

 life, it is generally used in a religious sense to 

 express one's relation to God. The system of 

 sacrifice established by Moses and described 

 in the first sixteen chapters of Leviticus shows 

 very clearly that these sacrifices were made to 

 secure reconciliation of the people with God 

 The sacrifice was an atonement for sin of the 

 person offering it and the great sacrifice made 

 by the high priest on the day of atonement, 

 once a year, was an atonement for the sins of 

 the nation. 



Little is said about the atonement in the New 

 Testament, but Roman Catholics and Protes- 

 tants alike agree that Christ, through his death, 

 me the atonement for the sins of the world, 

 and that all men can obtain forgiveness of 

 their sins by believing in Him. There is, how- 

 ever, considerable difference of opinion among 

 religious sects as to the method by which the 

 forgiveness may be secured. See SCAPEGOAT. 



JLTRIUM 



<>f atrium In the homes of wealthy 



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ATRIUM, a//' In urn. in tin- earl 



oin in which tin- fmtily life was 

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