Chemistry and Physics. 69 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Arrangement of Electrons in Atoms and Molecules. — 

 Irving Langmuir has presented an important contribution to 

 this interesting subject. He says that the problem of the struc- 

 ture of atoms has been attacked mainly by physicists who have 

 given little consideration to the chemical properties which must 

 ultimately be explained by a theory of atomic structure, and that 

 Kossell and also G. N. Lewis have had marked success in attack- 

 ing the problem in connection with the properties and relation- 

 ships indicated by the periodic system. Lewis has reasoned 

 from chemical facts that the electrons in atoms are normally 

 stationary in position, that they arrange themselves in a series 

 of concentric shells, the first shell containing two electrons, while 

 the other shells tend to hold eight. The outermost shell, how- 

 ever, may hold 2, 4, or 6 instead of 8. The eight electrons in a 

 shell are supposed to be placed symmetrically at the corners of 

 a cube or in pairs at the points of a tetrahedron, and when atoms 

 combine they are supposed to hold some of their outer electrons 

 in common, two electrons being thus held for each chemical bond. 



Kossell has conceived the electrons as located in a plane in con- 

 centric rings, rotating in orbits about a nucleus, and his theory 

 has many points of similarity to that of Lewis. It is pointed out 

 by Langmuir, however, that each of these theories in its present 

 form fails to explain the properties of a large part of the ele- 

 ments, especially those of higher atomic weights. 



Langmuir has therefore advanced a theory of his own, extend- 

 ing Lewis's idea of the cubical atom, and making use also of 

 certain ideas of Kossell. His speculative postulates and conclu- 

 sions are so numerous that no attempt can be made to give a 

 summary of them here, but a few aspects of his theory may be 

 presented. In attempting to determine the arrangement of elec- 

 trons in atoms he has been guided in the first place by the 

 numbers of electrons which make up the atoms of the inert gases, 

 in other words by the atomic numbers of these elements, namely, 

 helium 2, neon 10, argon 18, krypton 36, xenon 54, and niton 

 86. Bydberg has pointed out that these numbers are obtained 

 from the series 



N = 2(1 + 2 2 + 2 2 +3 2 + 3 2 + 4 2 +) 

 Langmuir draws the conclusion that these numbers represent 

 the electrons in perfect atoms with complete outer shells, and 

 thus decides upon the numbers of electrons in each shell. He 

 believes that the electrons of any given atom are distributed 

 through a series of concentric (nearly) spherical shells, all of 

 equal thickness, while the mean radii of the shells form an arith- 



